WalMart bike kicked my Ibis's ass!!- Mtbr.com
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  1. #1
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    WalMart bike kicked my Ibis's ass!!

    Ok so I go riding with my brother in Santee CA, I haven't ridden in that area before and my brother is telling me all about his $110 WalMart bike that they mismarked and he got for $65, which is about what my tires cost, he has been bragging about how good he is, I've been riding for many years and have brought my Ibis Silk Ti down, it has a nice Bomber Z2 fork on it, I'm confident I can ride circles around him. Well, we start going down this trail and a good speed, I'm thinking he is doing allright, then he startes going faster, and the terrain gets extremely rough, lots of baby heads everywhere, it's like a cobblestone highway. Well by now my bro is pulling away from me, sitting down and cruising like its a Sunday cruise, I'm using all my strength and skill trying to keep my bike straight, its bouncing all over these large cobblestones, I can't believe it, this can't happen, so about halfway down this trail I yell stop!! and I switch bikes with him. I climb on this Wally special, the handle bars are way up in the air and ultra tal front end, felt like riding a chopper, i swear the bike was almost as heavy as a Harley. I take his bike down the trail now, with its giant tractor weight tires, and to my disbelief, this heavy tank cheap ass bike, floats down the trail like a caddy!!! His heavy bike doesn't deflect on the rocks, the front wheel is like an immense gyroscope, nothing moves it! In the meantime my bro is laughing at my expensive bike, cause it totally sucks on this trail, and he is 100% correct. So I guess the moral of this story is...........?

  2. #2
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    Turn around, go up the hill. Then tell me, how is his Wally World bike?
    Start off slow & taper off from there.

  3. #3
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    you super-steep headtube angle probably isn't helping your stability much....

  4. #4
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    Or.........

    your just a crappy rider LOL
    Kidding!

  5. #5

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    Dude!

    No shyt! I have experienced the same thing. I have a Wally Mongoose that weighs in at about 40 lbs. It can mow thru some stuff my 2500 dollar K2 cant. I just don't get it!

  6. #6
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    Not me!

    See I dont have that problem I ride A Redline SS I just blow past anyone riding a wallyworld special...But in all fairness most of the riders who have them here arn't really pushing hard too bad I'd love to smoke em!

  7. #7
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    Your comment about weight and defelection...

    Quote Originally Posted by Itripper
    Ok so I go riding with my brother in Santee CA, I haven't ridden in that area before and my brother is telling me all about his $110 WalMart bike that they mismarked and he got for $65, which is about what my tires cost, he has been bragging about how good he is, I've been riding for many years and have brought my Ibis Silk Ti down, it has a nice Bomber Z2 fork on it, I'm confident I can ride circles around him. Well, we start going down this trail and a good speed, I'm thinking he is doing allright, then he startes going faster, and the terrain gets extremely rough, lots of baby heads everywhere, it's like a cobblestone highway. Well by now my bro is pulling away from me, sitting down and cruising like its a Sunday cruise, I'm using all my strength and skill trying to keep my bike straight, its bouncing all over these large cobblestones, I can't believe it, this can't happen, so about halfway down this trail I yell stop!! and I switch bikes with him. I climb on this Wally special, the handle bars are way up in the air and ultra tal front end, felt like riding a chopper, i swear the bike was almost as heavy as a Harley. I take his bike down the trail now, with its giant tractor weight tires, and to my disbelief, this heavy tank cheap ass bike, floats down the trail like a caddy!!! His heavy bike doesn't deflect on the rocks, the front wheel is like an immense gyroscope, nothing moves it! In the meantime my bro is laughing at my expensive bike, cause it totally sucks on this trail, and he is 100% correct. So I guess the moral of this story is...........?
    has some validity. Until recently I had a 24 lb. Superlight along with my Bullit. I've had this particular Bullit built in configurations from 28.5--32 lbs. The Bullit has repeatedly proven to be a better all-around trail bike for me on anything but the smoothest of trails--and I don't mean freeriding or DH. This lighter built-up Bullit is just much more pleasant to ride and doesn't get pinged all over the trail and is well worth the extra effort to pedal its weight up the hills. Now I wouldn't go out and buy a dual suspension Huffy, Pacific, etc., but a heavier duty mountain bike does have some advantages over a lightweight racer boy XC bike on rougher trails for sure. I'd like to see how long that Huffy is going to last with that kind of treatment. The forks and shocks that come on those level bikes are downright scary looking as far as design and quality are concerned.

  8. #8
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    So true... I have a Bullit too with triple clamp 170mm forks. This bike has edged out ALL of my other MTBikes as the one I ride ON EVERYTHING. With the 5th it is amazing and it makes every trail easier. Yes I said it even uphills. Now it is way way way slower on uphills but I can climb everything I could with my XC fs and ht bikes. I can climb tech sections on the Bullit the other bikes couldn't.

    I don't race so I am selling my other bikes becuase I don't need them anymore.

  9. #9
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    You already explained why the cheap bike decends better. High handlebar, slack head tube, and big tires. I have an Ibis Ripley and a Cannondale Jekyll. I can ride my usual trails faster on the Ibis because it is faster for XC. The speed lost on down hills is more than made up on flats and uphills. But there are a few technical decents I know of that are down right scary on the Ibis, but I could just about sit back and eat a sandwich while riding the Jekyll.

  10. #10
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    All walmart bikes have SUPER soft suspension, all of them. Mostly becaseu they are made for riding of the curbing max. They ride nice, but try and get the bike to fly, its scary.

    Also I used to beat the living piss out of my walmart bike. My new biek I am a little easier on.

    In no way is a walmart better than a good bike. Walmart bieks sucks. Screw them all.
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    I have a nice bike and a Wally bike to beat and work on, it's fun with both!

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    That's scary...

    As others have mentioned, next time ride the trail in the opposite direction and see who's laughing at the end of the day. Excess weight can be an advantage going down, but it's a big disadvantage going up.

    However, if I understand you correctly, your brother is riding extremely fast over extremely rough terrain, on an extremely inexpensive bike, correct? My concern would be, how long is it going to last before something fails catastrophically? Such a failure could easily result in a serious injury.

  13. #13
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    Something doesn't add up there. What type of suspension do you have? Have you tuned your suspension correctly?

    High speed hits are all about the damping and I'd imagine that the wally world bike would have pretty simple (friction ) damping.

    Or maybe your brother is a really good rider......

  14. #14
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    Hehe

    Quote Originally Posted by jkittlesen
    I have a nice bike and a Wally bike to beat and work on, it's fun with both!
    i've been thinking about getting a chepo fs bike to beat on, they r like so cool, everyone on my street has em don't think i'll bother wasting the cash though

    i had a cheepo fs bike, but it wore out and was not worth fixing. those things are like "disposable" MTB's

  15. #15
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    Nobody has really explained it yet so...

    When something has a greater mass it takes more force to move it. The WalMart bike with a higher weight will take the same hit at the same speed as a lighter bike and it won't react to the bump as much as the lighter bike will. This is regardless of the quality of the suspension to a very large degree.

    The most basic way to imagine this in physics terms is to think of two pool balls hitting each other. They both deflect equally. Now imagine a bowling ball and a ping pong ball hitting each other. The bowling ball will not be affected by the impact with the ping pong ball.

    A heavier bike just reacts less to terrain.

    Moral? Two parts: 1) You choose the right bike for what you want out of your riding experience. If you want to take those rough downhills more like that WalMart bike did get a heavier bike. 2) Think about the moral again in a few months when you both have ridden that trail several more times and you see how your respective bikes have weathered.

  16. #16
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    Quote Originally Posted by sliderhouserules
    Nobody has really explained it yet so...

    When something has a greater mass it takes more force to move it. The WalMart bike with a higher weight will take the same hit at the same speed as a lighter bike and it won't react to the bump as much as the lighter bike will. This is regardless of the quality of the suspension to a very large degree.

    The most basic way to imagine this in physics terms is to think of two pool balls hitting each other. They both deflect equally. Now imagine a bowling ball and a ping pong ball hitting each other. The bowling ball will not be affected by the impact with the ping pong ball.

    A heavier bike just reacts less to terrain.

    Moral? Two parts: 1) You choose the right bike for what you want out of your riding experience. If you want to take those rough downhills more like that WalMart bike did get a heavier bike. 2) Think about the moral again in a few months when you both have ridden that trail several more times and you see how your respective bikes have weathered.
    Close, but not quite right. When you hit a bump, either the ground gives or the bike & rider give. Most of the time it's the bike&rider .

    Now the object with less mass can move quicker than the object with more mass (inertia). This is why un-sprung weight is critical to suspension performance.

    Your bike shoud kick huffy butt in the suspension department.

  17. #17
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    Quote Originally Posted by Steve71
    Close, but not quite right. When you hit a bump, either the ground gives or the bike & rider give. Most of the time it's the bike&rider.
    This says nothing about a suspension system that's at least workable. If you're looking at how a bike reacts to terrain you can effectively ignore the rider factor and just look at the forces acting on the bike.

    When a bike hits a bump the front tire has a force exerted against it by the ground. That force is either transferred directly to the frame (in the case of a rigid fork), or a suspension fork absorbs some of the energy converting it from kinetic to thermal, dissipating it as heat. The back tire/suspension is no different. In the case of any kind of suspension, some of the force is still exerted against the frame. There is no perfect suspension designed that can absorb 100% of the force exerted against it without transferring some of that force to the frame. Since there is no suspension beyond the suspension (huh?) the force exerted against the frame results in movement of the frame.

    However, the frame exerts an equal and opposite force in two ways. The gravity is exerting force downward which is what brings your bike back down after a hit has forced it upward. Also, the frame has a tendency to want to stay where it was so it resists the force trying to move it with simple inertia. A heavier frame will exert a greater force in resistance to the force trying to move it than a lighter frame. This actually causes the suspension to have to absorb more of the force originally exerted against the bike by the ground.

    Of course this all happens pretty much instantaneously, but the plain language way to say it is, if you have two bikes with comparable geometries and close to equivalent suspension systems but different frame weights the heavier frame will react with less movement to the same hits from the ground. If the WalMart bike has a decent suspension (somebody said they felt pretty soft) and workable geometry then this factor (weight) will play a larger role in how well the bike takes hits.
    Last edited by sliderhouserules; 06-09-2004 at 05:49 PM. Reason: spelling

  18. #18
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    Quote Originally Posted by sliderhouserules
    .... heavier frame will react with less movement to the same hits from the ground.
    Were talking 10 lb difference here. Unless the rock gives, the bikes move about the same amount (suspension aside).

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    Quote Originally Posted by Steve71
    Were talking 10 lb difference here. Unless the rock gives, the bikes move about the same amount (suspension aside).
    The original post begs to differ. 10 pounds is actually a large amount when you're talking about 25 lb bikes. That's 40% more!

    Why does a Bullit take hits on a descent so much better than a Superlight? Geometry? Geometry has more effect on suspension efficiency than its ability to absorb bumps (within reason, I'm just saying this is a smaller factor). Travel? Yes, to a large degree. Frame weight? Well, this site is showing that a Bullit frame is nearly twice as heavy as a Superlight frame (~2500g vs. 4160g). I'm venturing that this factor plays the largest role of the three.

  20. #20
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    To further that thought...

    Quote Originally Posted by sliderhouserules
    The original post begs to differ. 10 pounds is actually a large amount when you're talking about 25 lb bikes. That's 40% more!

    Why does a Bullit take hits on a descent so much better than a Superlight? Geometry? Geometry has more effect on suspension efficiency than its ability to absorb bumps (within reason, I'm just saying this is a smaller factor). Travel? Yes, to a large degree. Frame weight? Well, this site is showing that a Bullit frame is nearly twice as heavy as a Superlight frame (~2500g vs. 4160g). I'm venturing that this factor plays the largest role of the three.
    Now we're all talking some generalization here, because obviously there are lots of other factors that come into play in some of the comparisons presented here, as you said. Since you touched on the Bullit/Superlight comparison that I made, and also mentioned geometry, I'll add that I had a 5" travel Psylo Race (air) on that Superlight which really slackens the head angle--so the geometry was not as much of a factor as it might normally be with a Superlight and 80mm fork.

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    Er,...you wouldn't happen to work for Wally's would you?

    ...This is beginning to sound a lot like an ad.

    Then again, as one reply rather boldly stated, in so many words, having an expensive bike, does not gaurantee skill or physical conditioning.

    I read somewhere that on a road bike, 2/3 of your energy is spent fighting the wind resistance against your body.

    I guess you could say that even a larger percentage than that, goes to fighting terrain and gravity on an mtb.

    The percentages certainly go up concerniong levels of skill and physical condidtioning, but it sounds like this was a trail he was showing you, and not only knew what was up ahead obstacle wise, but knew a good line to take as well.

    I seriously doubt the bike he had would hang with the Silk Ti on a long climb or endurence ride, given 2 equal riders.

    Two totally different bikes, made for different terrain.
    Last edited by Gnarlygig; 06-10-2004 at 01:06 AM.

  22. #22
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    Quote Originally Posted by sliderhouserules
    The original post begs to differ. 10 pounds is actually a large amount when you're talking about 25 lb bikes. That's 40% more!

    Why does a Bullit take hits on a descent so much better than a Superlight? Geometry? Geometry has more effect on suspension efficiency than its ability to absorb bumps (within reason, I'm just saying this is a smaller factor). Travel? Yes, to a large degree. Frame weight? Well, this site is showing that a Bullit frame is nearly twice as heavy as a Superlight frame (~2500g vs. 4160g). I'm venturing that this factor plays the largest role of the three.
    Well I stand by my original statement.

    Provided the bikes don't leave the ground, they are going to take the same (vertical) path over bumps regardless of weight (assuming they are both on the same line). Think about it, unless the ground gives, or the bikes gets air, they have no other option but the track the ground.

    Once again, the bike with less unsprung mass will have the potential for better suspension performance. But this is pretty small advantage when you consider the difference in damping (huffy vs Ibis).

    The reason a DH bike has better big hit capability is due to the suspension travel and the size and (lower) air pressue of the tires. Not to mention the bikes (frame, fork and wheels) flex a lot less which lets the suspension perform better. Frame flex is basicly a an un-damped spring.

  23. #23
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    Ha

    I know my bike is better and has a nice bomber z2 atom race on (80mm) it. It does well on most trails, but I was just surprised to see on this one particular trail the Wally bike was perfect for, and my bike was not suited for at all. It does make me think about building a heavier long suspension bike tho. When i built my Ibis I was riding a lot of fast twisty singletracks in Tennessee, those were a blast and my Ibis was perfect for them. Now I'm riding a lot of CA desert and semi arid trails in Mojave area. The trails here are sandy,gravely, and very rough in some spots, lots more severe up and downhills then Tenn. I wish I had at least a longer travel front shock for slacker angle and suspension. All I know is I will never judge a Wally bike again, it was a lot of fun to ride on that trail, and I would judge its weight to be at least 40 lbs

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    Quote Originally Posted by Itripper
    I know my bike is better and has a nice bomber z2 atom race on (80mm) it. It does well on most trails, but I was just surprised to see on this one particular trail the Wally bike was perfect for, and my bike was not suited for at all. It does make me think about building a heavier long suspension bike tho. When i built my Ibis I was riding a lot of fast twisty singletracks in Tennessee, those were a blast and my Ibis was perfect for them. Now I'm riding a lot of CA desert and semi arid trails in Mojave area. The trails here are sandy,gravely, and very rough in some spots, lots more severe up and downhills then Tenn. I wish I had at least a longer travel front shock for slacker angle and suspension. All I know is I will never judge a Wally bike again, it was a lot of fun to ride on that trail, and I would judge its weight to be at least 40 lbs

    It ain't the one trail, my guess it's the front fork. The atom is a light weight flexy fork. When it hits rocks it twists and flexes like crazy. I'm guessing the Walmart bike fork is built a lot heavier and flexes less. Plus tire size has a whole bunch to do with it bigger tires, better traction, less slipping off rocks and stuff. So you got a fancy cross country bike and they don't do downhills. But if you figure the time you save going uphill it will be more time than the downhill bike will gain on you on the downhill.

    One thing for sure is I wouldn't trust no Wallmart bike on a downhill unless I had personally gone over it. It's amazing how poorly those bikes are set up, with stuff not lined up and cables pinched and so forth. The bikes are set up by teenagers or clueless people. Plus the stuff is so cheap it won't hold up long for heavy trail use.

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    Quote Originally Posted by DrGlen51
    It ain't the one trail, my guess it's the front fork. The atom is a light weight flexy fork. When it hits rocks it twists and flexes like crazy.


    My 97' Z2 atom (70mm) was a killer fork (4.2lb). Very stiff with excellent damping. At least for my 150lb ass.

  26. #26
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    Material ???

    Something no one else mentioned was the material. Is your bike made of aluminum??? Well the 40lb Wally is probably steel. Steel flexes more than aluminum and provides a naturally "gentle" ride.

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    :)

    My Zoke isn't flexy, its very stiff, first time I have ever heard of a bomber being light weight and flexy, definetely not my experience, also not really a light fork either. And yes I am sure on almost any other trail I woulda kicked his ass!

  28. #28
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    It is the weight that makes the diff.

    You try riding a world class dh run on a XC bike & then ride it on a heavy dh rig, you'll see quickly that weight has a WWHHHOOOOOOLLLOOOTT to do w/it. Of course you have to factor in all of the other factors that have been mentioned, but weight will finally be the ultimate difference.....IMHO. Light weight bike will beat you to death, heavy bike will take alot of the puishment w/o transferin' it to your bones. Lighter weight bike is usin' your weight & its weight to absorb the impact.

  29. #29
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    For the first year that I rode, I rode 2 different wally bikes. One was a 39# fully ridged. The other was a #40 pogo full suspension.
    I passed lots of people on $3000 and had a great time doing it.
    I am alot faster now that I have a "real" bike.
    Before you criticize someone, you should walk a mile in his shoes...
    That way, when you criticize him you're a mile away and you have his shoes.

  30. #30
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    Quote Originally Posted by man w/ one hand
    You try riding a world class dh run on a XC bike & then ride it on a heavy dh rig, you'll see quickly that weight has a WWHHHOOOOOOLLLOOOTT to do w/it. Of course you have to factor in all of the other factors that have been mentioned, but weight will finally be the ultimate difference.....IMHO. Light weight bike will beat you to death, heavy bike will take alot of the puishment w/o transferin' it to your bones. Lighter weight bike is usin' your weight & its weight to absorb the impact.

    Weight the ultimate difference in when comparing an XC rig to a Dh one on a Dh course? Haha. Maybe you forgot about the huge travel on a DH rig and it's ability to float over the nasty stuff.

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    I agree with Sliderhouserules !!!!!!

    Been thinking of posting this weight thing on the weight board, am sure that no one on that board is going to agree. Ihave 2 FS bikes, both have comparable travel but the weights differ by about 8 pounds. When riding the lighter bike down a very rocky and steep section, the bike is deflected off of the rocks and is tough to handle vs. when I ride the heavier bike. The heavier bike just mowes them over.

    I own a metal fabrication factory and if you were to take a 5 pound hammer and hit something vs. a 1 1/2 pound hammer, you would understand what I am talking about.

    The key to this weight thing is to analyse what type of trails you ride on. and access the advantages/disadvantages. Personally I would much prefer to ride the 32 pounder up the hill because I live for the dropoffs and downhills.

    If I lived in S. Florida, I would definitely go with the lightest setup possible. The only thing to challenge you there is the speed you can ride, just like a road bike.

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    Is the geometry of those two bikes the same? I doubt it. I would bet one has alot slacker of a head angle.

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    Yuh, we'l see....

    How many times he'l kick your a$$ with that Wallly bike before it starts to fall apart and you leave him pushing it back from gods knows where.

    Gotta be an ego crusher though, sux to be you .

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    Quote Originally Posted by Ricko
    How many times he'l kick your a$$ with that Wallly bike before it starts to fall apart and you leave him pushing it back from gods knows where.

    Gotta be an ego crusher though, sux to be you .


    true, but he can get 10 wally bikes

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    Wrong !!!!!!

    Quote Originally Posted by Acme54321
    Is the geometry of those two bikes the same? I doubt it. I would bet one has alot slacker of a head angle.
    Head angle is the same....besides what does the angle have to do with the bike bouncing off the tops of baby heads vs. rolling over them ?? Even when the lighter bike had a LONGER travel fork, it did not matter. Heavy bike has it's advantages.

    In an obtuse way, think about a light long travel bike with the same amout of travel vs. a off road motorcycle coming down the hill.

    Try doing the experiment before commenting. You'll see the light.

  36. #36
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    ... and if we just ... Well, I got beat going uphill

    by someone riding a Mongoose. Not a LBS one, probably a Toy's R Us model with a kickstand on the left rear dropout.

    My excuse is that I already climbed 5 miles and he only had to do 2.5 or so. I also saw him chatting with some hiker earlier and then he passed me. So, he was well rested while I was pretty beat...

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    One word: S U B A R U ! ! ! ! !

    The Wally World bike probably has a geometry mildly similar to a freeride bike. The rider probably sits upright with their hands higher than their hips as opposed to your Ibis which probably makes you lean forward for fast, smooth trails. In this case, the price of the bike makes no difference. Your bike is expensive because it is custom made to be fast on flat and uphill terrain, not a DH like trail.

    Think of it this way, a beat up old rusty 4x4 pick-up worth $500 is going to descend a really rough, rocky trail a whole lot better than a brand new Subaru. Sure the Subaru might cost $28,000 and it might be all-wheel drive, but it's not really an off-road machine. It's meant to ride nicely and grip the pavement in all types of weather (Sorry all you Outback drivers who thought you had hardcore 4x4 machines...heh-heh) But compare the two vehicles on smooth terrain, the Subaru wins easily.

  38. #38
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    The ability to deflect impact is greater w/a heavy bike.

    Quote Originally Posted by Acme54321
    Weight the ultimate difference in when comparing an XC rig to a Dh one on a Dh course? Haha. Maybe you forgot about the huge travel on a DH rig and it's ability to float over the nasty stuff.
    Didn't forget that, what I'm sayin' is "If YOU ride a heavy rigid bike through a patch'o babyheads & then you ride a light rigid bike through afore mentioned babyheads, YOU will be able to tell a big difference how much better the heavy bike absorbs impact & does bounce off of the object as easy as the lighter bike does.

    Heavy bike = makes babyheads bonce off of it.
    Lighter bike = babyheads make bike bounce off of them.

    AND when lighter bike bounces off of babyheads it will transfer the impact to the rider.

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    Quote Originally Posted by man w/ one hand
    ...... "If YOU ride a heavy rigid bike through a patch'o babyheads & then you ride a light rigid bike through afore mentioned babyheads, YOU will be able to tell a big difference how much better the heavy bike absorbs impact & does bounce off of the object as easy as the lighter bike does.

    Heavy bike = makes babyheads bonce off of it.
    Lighter bike = babyheads make bike bounce off of them.

    AND when lighter bike bounces off of babyheads it will transfer the impact to the rider.
    I'm not sure if you were joking or not, but a heavy bike doesn't make babyheads bounce off it (provided the rocks are firmly attached to the ground). The mass of the babyhead and surrounding earth which absorbs the impact from the passing rider is huge in comparison to the difference in weight of the heavier bike.

    Unless the bikes leave the earth, they both travel the same path, because the earth (for the most part) doesn't 'give'.

    You would get stabilization from the extra gyroscopic force of the Huffies wheels though.

    But I think what you guys are taking about is when you're skimming over rocks. In that case, the heavy bike has more inertia. And inertia is a form of both compression & rebound damping. But the bike that maintains more contact with the ground will have more avaible grip. It will also be more active (ie bounce around more). So the huffy might feel more stable, but it's not tracking the ground because it's skimming more. That might be fine if it's in a straight line, but if you need to adjust your line, turn, or brake, then you have less avaible grip to do this.

    What feels faster and what is faster are not always the same.

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    Quote Originally Posted by JerryBoneJr
    Turn around, go up the hill. Then tell me, how is his Wally World bike?
    Exactly, I ride with a friend who rides an ibis silk ti. i ride a turner 5spot. he drops me going up, i drop him going down.

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    Weight Angles and Fat people.

    So someone is saying that 8lbs will make a large difference in how a bike handles rough down hill.

    So say I have a 25 lb bike and so does my friend EVERTHING BEING EQUAL save OUR BODY WEIGHT

    HE weighs 160 and weigh in at 200, do I have an advantage in this situation?

    Also, isn't the Geometry of the bike more important than the weight in this particular situtation? How much more or less so?

    That being said are there bikes out there that can adjust that geometry on the fly? So you can slacken the angles before doing the down hill part of the ride and thus have a more enjoyable ride all around???

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    I beat my wally every day..

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    Quote Originally Posted by Baldone
    So someone is saying that 8lbs will make a large difference in how a bike handles rough down hill.

    So say I have a 25 lb bike and so does my friend EVERTHING BEING EQUAL save OUR BODY WEIGHT

    HE weighs 160 and weigh in at 200, do I have an advantage in this situation?

    Also, isn't the Geometry of the bike more important than the weight in this particular situtation? How much more or less so?

    That being said are there bikes out there that can adjust that geometry on the fly? So you can slacken the angles before doing the down hill part of the ride and thus have a more enjoyable ride all around???
    The rider with more mass will take longer to turn and longer to slow for the corner. A lot of DH races are won and lost in the corners.

    I doesn't matter what you're racing. Weight is always the enemy

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    Quote Originally Posted by jadams35
    I beat my wally every day..
    ROTFLMAO

    Good one

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    Quote Originally Posted by Itripper
    So I guess the moral of this story is...........?

    Moral: Its not the arrows, its the Indian

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    Quote Originally Posted by Itripper
    His heavy bike doesn't deflect on the rocks, the front wheel is like an immense gyroscope, nothing moves it! In the meantime my bro is laughing at my expensive bike, cause it totally sucks on this trail, and he is 100% correct. So I guess the moral of this story is...........?
    The problems with cheapo bikes are:
    1) Suspension performance. If you just bomb straight and do not care about rattle, mildly irrelevant.
    2) Weight - not a big deal here. No need to accelerate. Big deal elsewhere.
    3) Durability - it will most likely break many times over. And fixing it is harder then with expensive bikes with standard parts.
    4) Safety - now, think hard about the headtube shearing off in the middle of that run.

    I own a crappy bike that I ride around occasionally. Costs cheaper then a set of clipless pedals for my training bike, or cheaper then a saddle on my race bike. It works fine - but I would not take it for a downhill ride. I value my body staying intact.

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    Yamon said it best...so far

    Quote Originally Posted by Steve71
    I'm not sure if you were joking or not, but a heavy bike doesn't make babyheads bounce off it (provided the rocks are firmly attached to the ground). The mass of the babyhead and surrounding earth which absorbs the impact from the passing rider is huge in comparison to the difference in weight of the heavier bike.

    Unless the bikes leave the earth, they both travel the same path, because the earth (for the most part) doesn't 'give'.

    You would get stabilization from the extra gyroscopic force of the Huffies wheels though.

    But I think what you guys are taking about is when you're skimming over rocks. In that case, the heavy bike has more inertia. And inertia is a form of both compression & rebound damping. But the bike that maintains more contact with the ground will have more avaible grip. It will also be more active (ie bounce around more). So the huffy might feel more stable, but it's not tracking the ground because it's skimming more. That might be fine if it's in a straight line, but if you need to adjust your line, turn, or brake, then you have less avaible grip to do this.

    What feels faster and what is faster are not always the same.
    Yamon said :
    "I own a metal fabrication factory and if you were to take a 5 pound hammer and hit something vs. a 1 1/2 pound hammer, you would understand what I am talking about."

    my .02 : hang a babyhead size rock from a string, tie a steel ball bearing to a string & swing it into the rock. Measure how far it bounces off. Now tie a hollow metal ball to the string & swing it into the rock & measure the distance it bounces. The denser mass = dh bike, will absorb hit better AND not transfer it to rider as bad as the mass w/ lessr density= XC bike. Thus allowing better control of said denser mass = dh.

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    Quote Originally Posted by man w/ one hand
    Yamon said :
    "I own a metal fabrication factory and if you were to take a 5 pound hammer and hit something vs. a 1 1/2 pound hammer, you would understand what I am talking about."

    my .02 : hang a babyhead size rock from a string, tie a steel ball bearing to a string & swing it into the rock. Measure how far it bounces off. Now tie a hollow metal ball to the string & swing it into the rock & measure the distance it bounces. The denser mass = dh bike, will absorb hit better AND not transfer it to rider as bad as the mass w/ lessr density= XC bike. Thus allowing better control of said denser mass = dh.
    Heavier objects resist movement more than lighter objects, we agree on that. It's is called mass damping . A heavy bike will move around less, I agree on this as well.

    However, unless the bikes get a hit that causes them to leave the ground, both bikes will travel the exact same path (do you not agree on this ). And I'm also saying that although that ( the extra weight) might feel good, or stable, it's not going to be faster, for the reasons I've stated in my last post.

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    Quote Originally Posted by Steve71
    Heavier objects resist movement more than lighter objects, we agree on that. It's is called mass damping .
    This is more correctly termed inertia or the inertial mass of an object. Mass damping is external forces acting upon a system to nullify motion. The perfect example of this is an object suspended from a spring. If you displace the object away from the equilibrium point of the spring and then release it the object will oscillate in simple harmonic motion (IE indefinitely) unless acted upon by some outside force. Of course, all springs have internal friction which resists this motion, and if there is air present air-resistance (another form of friction) will also resist the motion. These friction forces will eventually bring the object to rest at the spring's equilibrium point where it will stay. These friction forces would be the damping forces in this system.


    Quote Originally Posted by Steve71
    A heavy bike will move around less, I agree on this as well.
    This is the crux of the point that I (and others, in my estimation) have been trying to make. Are you trying to make an alternate point that is just seeming (at least to me) to be actual disagreement with this point?


    Quote Originally Posted by Steve71
    However, unless the bikes get a hit that causes them to leave the ground, both bikes will travel the exact same path (do you not agree on this ).
    This is something you keep saying and I've tried to counter above because no, it is not true. It is true if you're talking about completely rigid bikes, but if a bike has any kind of suspension at all then the suspension is going to absorb some of the vertical displacement caused by the terrain and not transfer it to the frame (where it would be felt by the rider).


    Quote Originally Posted by Baldone
    So someone is saying that 8lbs will make a large difference in how a bike handles rough down hill.

    So say I have a 25 lb bike and so does my friend EVERTHING BEING EQUAL save OUR BODY WEIGHT

    HE weighs 160 and weigh in at 200, do I have an advantage in this situation?
    Yes and no. In the context of the pure argument that we (well, me at least) have been debating the answer is no, because what we're talking about is which of the bikes is more comfortable going over bumps downhill, which can also be said as which of the bikes absorbs the bumps without transferring the force or motion through to the rider. Since the point to examine is the point where the bike meets the rider and the thing to examine is how much force is transferred from the bike to the rider then you have to look at the system without the weight of the rider being a factor. Look at it this way, the bike is going to press upward against a heavy rider just as hard as against a lighter rider. This is essentially the same point as the suspension pressing upward against a light bike vs. a heavy bike. The heavy bike will feel the same force, but will react less to it. A heavy rider will feel the same force from the bike, but will be moved less by it.

    Now if you're just wanting a simple answer to the subjective "advantage" question then the answer is probably yes, because your heavier weight will in turn keep your bike from reacting to the terrain as much as a lighter rider on the same bike would. So the whole system of bike + rider will absorb the bumps with less displacement. But you're still going to feel the force just as much. How it feels to you will, of course, be subjective, but empirically the force exerted against your body will be the same.


    Quote Originally Posted by Steve71
    And I'm also saying that although that ( the extra weight) might feel good, or stable, it's not going to be faster, for the reasons I've stated in my last post.
    This also isn't true. In conjunction with the point that a heavier bike will not be moved by an impact as much as a lighter bike will, a heavier bike will also not be slowed down as much as a lighter bike will. A rock field will actually slow a bike down due to components of the forces exerted by the rocks and bumps against the bike that are opposite the direction of motion (IE a rock exerts a force upward against a bike, but it also exerts a force backward, or opposite the direction of motion, against the bike).


    Quote Originally Posted by Baldone
    Also, isn't the Geometry of the bike more important than the weight in this particular situtation? How much more or less so?
    It can, but when the geometries of a bike are close enough that you could call them "similar" then the bigger difference will come from the weight of the bike. I'm not stating this as fact. As I've said before, I'm really postulating this, venturing that weight will make the bigger difference. This is just an ascertation I've made from riding some different bikes -- some heavy, some light.

    What if you're looking at two bikes that have very similar geometry? How much better will the heavier bike handle? How much weight difference does it take to make it handle noticeably better?

    What about two bikes that are exactly the same weight? How much difference in geometry does it take to make one handle noticeably better?

    Now split the geometry question above in half and think about how much difference there is in the rear suspension geometry of most bikes. Amount of travel does not equate to different geometry in all respects. The rear wheel path during compression more accurately equates to different geometry. How different is the rear wheel travel of most bikes? When you start to examine that question you get into different debates (active vs. jacking, 4-bar vs. single pivot) and most of those arguments don't usually focus on raw suspension performance (IE bump absorption or how smooth the ride is). The geometry of the front end is noticeably different in XC vs. DH rigs, but not considerably. Three degrees max or so? That's not that much, really (1%).


    Quote Originally Posted by Baldone
    That being said are there bikes out there that can adjust that geometry on the fly? So you can slacken the angles before doing the down hill part of the ride and thus have a more enjoyable ride all around???
    The Fox TALAS fork does this exact thing (and there are others -- Marzochii (?) ETA, et al). It's generally marketed the other way though -- you sharpen the angle of the bike before you take the uphills to help you climb better, then you relax the fork back to the natural position before you go downhill.

    The performance, the damping ability of a suspension are secondary to the raw ability of a suspension to simply absorb bumps. If a bike has passably workable suspension that can absorb bumps well then the rider will feel it less when a bump is hit. There's no simpler way to say it. And if you're still not following what I'm trying to explain imagine some basic physics experiments:
    • Stack a few large books on top of someone's head, then put a piece of 2x4 on top of those. Now take a nail and a hammer and drive the nail into the piece of wood (just a stroke or two of the hammer). The person under the books will hardly feel the hammer hit at all.
    • Hold a brick in your hand and hit it with a hammer hard enough to break the brick. Your hand will hardly feel the force of the hammer hit.
    These are both common experiments carried out in classrooms to demonstrate the principle of Inertia and Newton's Laws of Motion. In both of the cases above the large mass of the objects (the books, the brick) resists the force of the hammer enough that they don't move and transfer that force to the person. This is the same with a heavy bike. It will absorb the forces of terrain and not transfer those forces to the rider as much as a light bike will.

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    I am in agreement ......

    w/Steve71 & sliderhouserules. Very well put, both of you. Yes we are trying to say the same things. Seems alot of the time on here, (& in life in general), we seem to be saying the same things but it seems we are disagreeing because of each individuals wording or inflection. Too many factors involved in things nowadays to find "absolute truth". We can focus on a factor in any situation to justify our reasoning. Each of us have become "lawyers," giving us the ability to "plead our case" w/conviction, for lack of a better term, & we know, we are right, period. Each of us have been taught to stand up for ourselves to the point that we aren't going to let anyone tell us we are wrong, because we "know" this is "true" - for us.
    Makes for some hi-tensioned interaction w/others, and after it happens enough, we come to expect it in any, & even worse, ALL situations. Gettting out on my bike lets me get rid of all of this junk in my head & wind down from the day. Have to be carefull about getting on here an' chimmin' in w/my .02 too, cause it starts all over again if we aren't carefull.

    Don't mean any disrespect to anyone but, one of the members here, can't name him off of the top of my head, says it best at the bottom of his posts,

    "Arguing on the internet is like the special olympics, even if you win - your still retarded".

    Again I mean no disrepect to anyone. But it really does put things in perspective. Again my .02.

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    Quote Originally Posted by man w/ one hand
    Don't mean any disrespect to anyone but, one of the members here, can't name him off of the top of my head, says it best at the bottom of his posts,

    "Arguing on the internet is like the special olympics, even if you win - your still retarded".

    Again I mean no disrepect to anyone. But it really does put things in perspective. Again my .02.
    Aye, I have gone a bit overboard in this thread. Apologies. Debating the nit-picky details is fun sometimes but it can also be taken the wrong way, and does tend to make you (me) out to be a know-it-all when you (me) do argue the nit-picky details.

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    Yo slider house

    Not directed to any ONE person here...I was just thinkin' out loud. Most folks have good valid points. Most of us would most likely have te same view on things if we all had access to the same info., but we don't & thats what we are on here for. I'm more than happy to see things your way, IF you have valid info & points. I may not be from Missouri, but your gonna need to "show me". I can be swayed.

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    Quote Originally Posted by sliderhouserules
    This is more correctly termed inertia or the inertial mass of an object. Mass damping is external forces acting upon a system to nullify motion. The perfect example of this is an object suspended from a spring. If you displace the object away from the equilibrium point of the spring and then release it the object will oscillate in simple harmonic motion (IE indefinitely) unless acted upon by some outside force. Of course, all springs have internal friction which resists this motion, and if there is air present air-resistance (another form of friction) will also resist the motion. These friction forces will eventually bring the object to rest at the spring's equilibrium point where it will stay. These friction forces would be the damping forces in this system.
    I guess you missed my point, so I'll explain it again . What we're more concerned with is the resonant frequency of the bike. The bike isn't a mass attached to a undamped spring (for simplicity sake we consider the fame a perfectly rigid structure). For example, the bike is rolling along the ground and it being excited (hit) by rocks that are at intervals such that each consecutive impact builds upon the previous one. We've all experienced this. All of a sudden, the bike starts to "buck or bounce" more and more with each successive impact. We can then say it's being excited by its resonant frequency. If we alter the mass of the bike in either direction, we will alter the resonant frequency of that bike. So in effect, the extra mass provides damping.

    As I'm sure you know, damping takes all shapes and forms and damping does not infer crital damping.

    When I was studying for my degree in Microelectronic Engineering, we covered damping in great depth. Electrical and Mechanical engineering are pretty similar, but in electronics, we're concerned with the damping of electrical signals rather than displacement of physical objects.

    Quote Originally Posted by Steve71
    A heavy bike will move around less, I agree on this as well.
    Quote Originally Posted by sliderhouserules
    This is the crux of the point that I (and others, in my estimation) have been trying to make. Are you trying to make an alternate point that is just seeming (at least to me) to be actual disagreement with this point?
    Do you agree that the bike that has more time in contact with the ground has more potential for speed?

    Think about it like this. The wheels of a rigid bike move around less than the wheels of a bike with 6" of travel. Note, I'm just talking about wheels here, not what the rider feels though the bars and pedals. So you can see here, that although, the 6" travel wheel is moving around more, it's also in contact with the ground more and therefore it has more avaible grip and therefore is faster. So the premise that the object that moves around less is faster is false.

    Now think about this. Your bike has 4 levels of suspension. (1) Tires (2) shocks (3) frame/wheel handlebar flex etc (4) arms and legs.

    All of those levels of suspension have some damping except the bike flex. Now the contact points of the lighter bike are moving around more just like the wheel of a 6" travel bike. Provided that your arms and legs can provide travel and damping for that movement, then ..... well you can see the parallels - it's just like the wheel which moves around more.

    As I've said, the ground doesn't move, so the bikes ability to flow quickly over objects while keeping in contact with the ground is critical. The less mass an object has, the less resistance to movement it will have. However, mass as I said before changes the resonant frequency of the bike, so in some situations, the extra mass could provide better damping, but the other 99% of the time it's a hindrance.

    Quote Originally Posted by Steve71
    And I'm also saying that although that ( the extra weight) might feel good, or stable, it's not going to be faster, for the reasons I've stated in my last post.
    Quote Originally Posted by sliderhouserules
    This also isn't true. In conjunction with the point that a heavier bike will not be moved by an impact as much as a lighter bike will, a heavier bike will also not be slowed down as much as a lighter bike will. A rock field will actually slow a bike down due to components of the forces exerted by the rocks and bumps against the bike that are opposite the direction of motion (IE a rock exerts a force upward against a bike, but it also exerts a force backward, or opposite the direction of motion, against the bike).
    You're argument is based on the fact that a heavy object will be deflected less due to it's mass. Now while this statement is correct, when you apply the theory to the example of bike vs. earth, the extra 10lb of bike is insignificant.

    For the formulas for laws of conservation of momentum and energy check out

    http://www.euclideanspace.com/physic...ollision/oned/.

    The long and the short of it is that the the total momentum of the two objects is the same before and after the collision.

    For simplicity sake, lets say the earth has infinite mass and is at rest. This basically means that the whatever momentum the bike has before the impact, it will have the same momentum after the impact, just in the opposite direction.

    So your statement that a "heavier bike will also not be slowed down as much as a lighter bike will" is incorrect. Or have I missed something
    Last edited by Steve71; 06-22-2004 at 12:40 PM.

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    Quote Originally Posted by sliderhouserules
    Aye, I have gone a bit overboard in this thread. Apologies. Debating the nit-picky details is fun sometimes but it can also be taken the wrong way, and does tend to make you (me) out to be a know-it-all when you (me) do argue the nit-picky details.
    I enjoy a good debate. It's only when it turns into a name calling fest that both parties look retarded .

    If were still arguing physics, it's all good in my book .
    Last edited by Steve71; 06-22-2004 at 01:00 PM.

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    It's all fun-n-games till someones eye gets put out...

    then it's Hillarious!!!!

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    This has stayed clean and is interesting for me so I'm going to keep it going. I'm a bit perplexed, though, by the points you're trying to make Steve71. The things you have been arguing seem to be stating that the Ibis bike will perform better than the WalMart bike, yet ltripper's whole point was that it didn't. I don't see where you are trying to answer the question of this thread.

    Let me outline some key points and we'll see where that takes us.

    What are we really looking at?
    A light, high-quality Ibis bike was outperformed by a "tank-heavy", "cumbersome tractor-tire" low-quality Walmart bike on a rough downhill descent. Why?

    The Ibis bike beat the hell out of both riders and the Walmart bike didn't. Why?

    Why? Because the Walmart bike has a heavier frame. The respective geometries of the bikes are surely different, but the weight of the frame is the single most important factor here. A bike is not a simple object; it is a complex object with moving parts -- namely a suspension system designed to dissipate the forces of terrain impact without transferring those forces to the frame and subsequently to the rider.

    That is the whole point here. The suspension system of the Walmart bike absorbed the forces of terrain impact without transferring those forces to the frame of the bike. If those forces had been transferred to the frame the frame would have moved in response and the rider(s) would have felt it, and either sucked it up with their suspension system (their arms and legs) or been moved themselves in response.

    So the crux of the question is how does a bike suspension absorb impact forces without transferring those forces to the frame. You can't try to examine the bike as a rigid structure -- the suspension is key, you can't take it out of the picture. If you do you change the entire argument. Neither of these bikes was a rigid bike. We don't need to look at rigid bikes to examine this problem. A suspended bike is not going to travel the same vertical path over a bump as a rigid bike will. The wheels will, but the frame won't. If you don't agree with that point then we need to stop right there. The dynamics of a suspension system are what we're looking at.

    What's involved in "suspension"?
    I like to think of the two facets of a suspension system as shock absorption and rebound damping. I know the first one also qualifies as damping, but I think it can be confusing to call it this since the damping adjustment of most shocks and forks has little or nothing to do with compression damping. It is merely the rebound damping adjustment -- IE how quickly the system returns to the neutral position. I think the question of this thread has very little to do with the rebound damping performance of these two bikes. I think it has everything to do with the shock absorption ability of these two bikes. The tire receives an impact, does it get transferred through to the frame?

    We don't need to look at repeated impacts to find the answer. We aren't concerned with the resonant frequency of the bikes. We just need to analyze each bike's ability to absorb an impact. We can do this just as easily by looking at a single impact, a single bump. The difference in these two bikes will be completely apparent by analyzing how they take a single bump.

    Can this be envisioned as a simple model?
    A bike is actually one of the best real-world examples of a mass attached to a spring. If you don't think so, then I would guess the imaginary model you have in your mind is a rock or weight hanging from a Slinky-type spring, right? Well, that obviously doesn't model a bike. But all you have to do is turn that model upside-down, change the spring into one that resists compression (a stiff spring) rather than one that rebounds when you pull on it (a Slinky spring), and you have a simplified representation of a suspended bike frame. The weight or rock is the bike frame, the spring is the suspension, and whatever the spring attaches to represents the ground (or the wheels).

    I worked up a couple graphics to demonstrate what I'm talking about. One shows a single spring system representing nothing but the bike frame, the bike suspension, and the ground/wheels. The second one includes an additional spring system on top of the first to represent the rider's weight and attachment to the bike. In each of them, the board representing the ground has pins that can travel freely up the slots in the rigid gray uprights. (We can disregard friction and any complexities of the board getting crooked. Just pretend it's lubed up nicely and stays perfectly horizontal at all times. ) Consider the springs rigid enough to hold up the weight on top of them without falling over.

    We can really look at the entire problem using just the first graphic, disregarding the weight and input of the rider, as I've mentioned before. To show what happens when a bike hits a bump we need to simulate the ground moving up and down with a quick single movement on our model. When we do, we want to watch what it does to the weight that represents the bike frame to see if and how much it moves.

    Now, really try to imagine this and think about it. If the bottom spring has to compress in response to a force, it will exert that force against the weight on top of it. If Block B weighs 5 lbs and you hit the board that represents the ground with a strong force (say 25 lbs) Block B is surely going to be moved upwards by the spring. But what about if Block B weighs 50 lbs? It will move hardly at all when the spring receives the same 25 lbs force. I'm just pulling 25 lbs out of the air. I have no idea what kind of force the ground exerts against the tire. And a stiffer spring will make a world of difference. But do you believe that it will happen that way? Do you believe the heavier weight will hardly move in response to the same force? If you don't then we need to stop right there because all of the basic physics that are happening in this system can be demonstrated with that simple model.

    What are the forces that act on a bike?
    When a bike encounters a bump-type change in the terrain there is a force exerted against the tires -- IE the ground is trying to make the bike move upwards. The tires/wheels of a bike are going to be moved upwards no matter what -- as you've said, the ground does not "move". The unsprung components of the bike simply transfer that same force (minus what little bit the tires can absorb) directly to the spring system that is the suspension. The springs of the suspension do the same thing by exerting that force against their upper attachment (the bike frame), except that a spring is a special structure that has the ability to compress and dissipate the energy of movement. When the spring exerts a force against the upper object (the frame) that object on the other end (the frame) is going to resist that force with its inertial mass. Heavier objects have more inertial mass. If the object has a high enough inertial mass the spring will be caused to compress. If it has a low enough inertial mass the spring won't need to compress because the object will move. Even if one object (frame) is only slightly heavier than another object (frame) it will have a higher inertial mass to resist that force with, and will therefore cause the springs to have to absorb more of the force or movement (even just a little bit).

    A heavier frame will not be moved as much as a lighter frame. If you can agree with this I'm not sure why the argument needs to go any further. There are other considerations, but this is the main point. This is a fairly complete look at the physics involved.

    What else is involved in how a bike handles?
    One thing we could talk about is the difference in geometries, but since we don't have comparisons of these bikes actual geometries it would be general bike geometry theory. Since the impact of terrain against a tire is generally a force in a diagonal upwards direction, a slacker head angle will more closely align the fork's direction of motion to this force allowing it to more efficiently absorb the impact. Any quality suspension, however, will still be able to absorb the impact to much the same degree. The difference is, any components of the force that are perpendicular to the fork's direction of motion will not be able to be absorbed by the fork, and will result in other things happening, like slowing down the bike, or deflecting the front wheel. [edit]A more upright fork (steeper head angle) will leave more horizontal components of the force of impact to be dealt with other ways -- IE it will absorb less of the force of impact.[/edit]

    We could also talk about tire + wheel weight, which has been mentioned already. Heavier wheels will have more gyroscopic effect which will help them stay straight when they receive terrain impacts. This helps to alleviate the effects of what I mentioned in the previous paragraph -- front tire deflection. It can also have an effect on suspension performance but it deals with rebound performance more than anything so it doesn't have much bearing on the overall question we've been dealing with.

    One other thing we could talk about is the effect a rider's weight has on the system. If you take my second graphic and envision how the same experiments work with the upper block (Block A) always being a constant weight that is something close to five times the weight of the lower block (Block B) it will help to keep the lower block from moving even more, but only because the upper spring will be caused to compress. Since the upper spring represents the rider's arms and legs any compression in this spring is force felt by the rider, and the thing we've been examining is a bike's ability to absorb the force of an impact without transferring that force to the rider. So it's almost irrelevant.


    There are a couple specific points I want to respond to:

    Quote Originally Posted by Steve71
    Do you agree that the bike that has more time in contact with the ground has more potential for speed?
    I absolutely disagree that the bike that has more time in contact with the ground has more potential for speed. We're talking about a downhill descent here, not an uphill climb, or even a flat traverse.

    Take two steel marbles and drop them from the same height... which one is traveling faster when it hits the ground? Neither, they'll both be traveling at the same speed if they're dropped from the same height.

    Now, take two steel marbles and drop one from a certain height and send the other one down a smooth inclined plane starting at exactly the same height. Which one will be traveling faster when it reaches the ground? Again, neither. The one going down the plane will take longer to get there, but it will be traveling at the exact same speed as long as there is nothing slowing it down.

    Now factor in a small bit of friction for the marble you roll down the inclined plane (because there is some). That little bit of friction will shave off a bit of speed so the marble rolling down the inclined plane will actually be traveling slower than the free-fall one by the time it gets to the bottom.

    Now change that smooth inclined plane into one that is similar to a "cobblestone highway" for its full length. The marble you roll down that incline will not be going anywhere near as fast as the free-fall one, or the smooth plane one, for that matter.


    Quote Originally Posted by Steve71
    ...it's also in contact with the ground more and therefore it has more avaible grip and therefore is faster. So the premise that the object that moves around less is faster is false.
    "Grip" when you're going downhill will be the primary factor in slowing you down not speeding you up. Free-fall provides the fastest acceleration, and any contact with the ground will generate friction which slows acceleration/velocity. The more contact you have with the ground the more friction you have between you and the ground so the more it's going to slow you down.

    When your tires, not gravity, are propelling your bike then more contact with the ground will allow you to go faster, yes, but this doesn't hold true when you're going downhill.

    Now whether you want to keep your tires in contact with the ground when you're going downhill, even though it will slow you down, is another matter. In general, you want to be able to control (check) your speed going downhill, so contact with the ground is guud. It's not going to help you go faster though.


    Quote Originally Posted by Steve71
    As I've said, the ground doesn't move, so the bikes ability to flow quickly over objects while keeping in contact with the ground is critical.
    Critical for what? Suspension performance, sure. A suspension that skips over repeated bumps is not as efficient as one that tracks the ground nicely over those bumps, but that is not the primary concern here. Raw ability to absorb an impact is. Not to mention, the Walmart bike was handling just fine, even if it was skipping over the rocks (which we aren't sure about). What does that say about the relevance of analyzing this? To me it says it isn't relevant at all.


    Quote Originally Posted by Steve71
    ...
    The long and the short of it is that the the total momentum of the two objects is the same before and after the collision.

    For simplicity sake, lets say the earth has infinite mass and is at rest. This basically means that the whatever momentum the bike has before the impact, it will have the same momentum after the impact, just in the opposite direction.

    So your statement that a "heavier bike will also not be slowed down as much as a lighter bike will" is incorrect. Or have I missed something
    You've missed the whole idea that momentum, or the energy of movement (kinetic) can be converted into heat (thermal) energy. This is exactly what a suspension system does.

    After a bike traverses a bump in the trail it will not have the same momentum as it did before it hit the bump. It will be going slightly slower and the shocks will be a slightly higher temperature.

    Roll a pool ball down an inclined plane and see how hard it is to stop it at a certain point with your hand. Now roll a bowling ball down the same incline and stop it at the same point with your hand. The heavier object has more momentum overall. A bump that exerts a certain force against a bike will exert that same force against a lighter bike. The heavier bike will have more momentum to begin with and so proportionately will not be affected as much as a lighter bike will. We can get into this one more if you want, but let's deal with the other stuff first.
    Attached Images Attached Images
    Last edited by sliderhouserules; 06-25-2004 at 12:22 PM.

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    I don't know if this was mentioned yet, because there was too much to read and too little time, but....

    Not just turn around and try to ride it uphill, but bring it here to the mid atlantic, and try to ride the Wally beast through our nice sticky mud. You'll be hating life. Not to mention the fact that the cheap components will stop shifting and braking (as opposed to breaking) properly.

    I went out to Denver on business a few weeks ago and went mountain biking with a friend at Red Rocks. I rented a bike that retailed for $350. What I noticed was that the bike constantly felt like it was about to fall apart, even though it was brand spanking new (they took the price tags off it when I rented it). The biggest problem was that both the front and rear shoks were basically pogo sticks, and soft ones at that. So, while it could easily take the shock of running into a rock or root, as soon as the wheel came off it, it just sprung back with a good amount of violence. I found that it seemed to work better at speed (except for the feeling of impending doom, that the bike would just disintegrate underneath me) over the small rocks and bumps. I came away with a distinct understanding of the value of the >$2k that I have in my GF Sugar.

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    Good post SH . It's nice to have a civil discussion.

    I can see where weíre disagreeing (I think) and Iíve gone into it in detail below.
    BTW if itís not apparent, the tone of the post is meant to be nice. Seems that you know what youíre talking about, but IMHO are missing a few important details which makes a big change to the outcome. But my physics is far from perfect, so if itís actually me who missing something, let me know.

    Quote Originally Posted by sliderhouserules

    I'm a bit perplexed, though, by the points you're trying to make Steve71. The things you have been arguing seem to be stating that the Ibis bike will perform better than the WalMart bike, yet ltripper's whole point was that it didn't. I don't see where you are trying to answer the question of this thread.
    Not to be rude, but since it wasnít a controlled experiment, ltripper experience is anecdotal. But this discussion is now more about, ďis a bike with a heavier frame faster due to itís extra mass?Ē And there are a few things being said that I donít agree with, so Iím just stating my case.

    Quote Originally Posted by sliderhouserules
    The Ibis bike beat the hell out of both riders and the Walmart bike didn't. Why?

    Why? Because the Walmart bike has a heavier frame. The respective geometries of the bikes are surely different, but the weight of the frame is the single most important factor here
    I donít agree with the weight being the single most important factor. Damping, suspension travel & design, geometry, damping, frame/fork/wheel rigidity and tires (and tire pressure) are all going to come before the weight of the frame. And extra frame weight is a hindrance anyway (provided it doesnít add stiffness).

    Quote Originally Posted by sliderhouserules
    What are the forces that act on a bike?
    When a bike encounters a bump-type change in the terrain there is a force exerted against the tires -- IE the ground is trying to make the bike move upwards. The tires/wheels of a bike are going to be moved upwards no matter what -- as you've said, the ground does not "move". The unsprung components of the bike simply transfer that same force (minus what little bit the tires can absorb) directly to the spring system that is the suspension. The springs of the suspension do the same thing by exerting that force against their upper attachment (the bike frame), except that a spring is a special structure that has the ability to compress and dissipate the energy of movement. When the spring exerts a force against the upper object (the frame) that object on the other end (the frame) is going to resist that force with its inertial mass. Heavier objects have more inertial mass. If the object has a high enough inertial mass the spring will be caused to compress. If it has a low enough inertial mass the spring won't need to compress because the object will move. Even if one object (frame) is only slightly heavier than another object (frame) it will have a higher inertial mass to resist that force with, and will therefore cause the springs to have to absorb more of the force or movement (even just a little bit).

    A heavier frame will not be moved as much as a lighter frame. If you can agree with this I'm not sure why the argument needs to go any further. There are other considerations, but this is the main point. This is a fairly complete look at the physics involved.
    What you say is correct, but incomplete. If youíre going to compare apples to apples, you would need a slightly lighter spring in the case of the lighter frame. So then both bikes would respond exactly the same to the same upward impact from the fork (unless the fork bottoms Ė then it will act as a ridged bike), given the same static load (the rider). You canít compare the suspension performance of two bikes unless they have the same amount of sag.

    Thatís why you can have the same suspension performance from a bike with a 150lb rider and a 200lb rider. You adjust the spring. In your example, youíre not adjusting the spring to compensate for the lighter static load.

    Quote Originally Posted by sliderhouserules
    I like to think of the two facets of a suspension system as shock absorption and rebound damping. I know the first one also qualifies as damping, but I think it can be confusing to call it this since the damping adjustment of most shocks and forks has little or nothing to do with compression damping. It is merely the rebound damping adjustment -- IE how quickly the system returns to the neutral position. I think the question of this thread has very little to do with the rebound damping performance of these two bikes. I think it has everything to do with the shock absorption ability of these two bikes. The tire receives an impact, does it get transferred through to the frame?

    We don't need to look at repeated impacts to find the answer. We aren't concerned with the resonant frequency of the bikes. We just need to analyze each bike's ability to absorb an impact. We can do this just as easily by looking at a single impact, a single bump. The difference in these two bikes will be completely apparent by analyzing how they take a single bump
    I donít really agree with that. The components that make up a suspension system and effect itís performance are

    (1) Travel
    (2) Rebound damping
    (3) Compression damping
    (4) Spring rate
    (5) Un-sprung mass
    (6) Static load

    Looking at the bikes ability to absorb a single impact isnít going to tell you much about its ability to handle a rock garden (which requires well tuned rebound damping).

    Quote Originally Posted by sliderhouserules
    I absolutely disagree that the bike that has more time in contact with the ground has more potential for speed. We're talking about a downhill descent here, not an uphill climb, or even a flat traverse.

    "Grip" when you're going downhill will be the primary factor in slowing you down not speeding you up. Free-fall provides the fastest acceleration, and any contact with the ground will generate friction which slows acceleration/velocity. The more contact you have with the ground the more friction you have between you and the ground so the more it's going to slow you down.

    When your tires, not gravity, are propelling your bike then more contact with the ground will allow you to go faster, yes, but this doesn't hold true when you're going downhill.

    Now whether you want to keep your tires in contact with the ground when you're going downhill, even though it will slow you down, is another matter. In general, you want to be able to control (check) your speed going downhill, so contact with the ground is guud. It's not going to help you go faster though.
    Well I do agree with you that the less contact you have with the ground the less friction (which will slow you down slightly) there is.

    But there is less grip also. And the less grip you have, the longer it takes you to stop and turn. Stopping, checking your corner entry speed, adjusting you line, carving a turn can all be done faster when you have more grip.

    There are precious few examples of DH terrain where giving up grip for rolling resistance (up to a point) is going to get you to the finish line faster.

    Quote Originally Posted by sliderhouserules
    You've missed the whole idea that momentum, or the energy of movement (kinetic) can be converted into heat (thermal) energy. This is exactly what a suspension system does.

    After a bike traverses a bump in the trail it will not have the same momentum as it did before it hit the bump. It will be going slightly slower and the shocks will be a slightly higher temperature.

    Roll a pool ball down an inclined plane and see how hard it is to stop it at a certain point with your hand. Now roll a bowling ball down the same incline and stop it at the same point with your hand. The heavier object has more momentum overall. A bump that exerts a certain force against a bike will exert that same force against a lighter bike. The heavier bike will have more momentum to begin with and so proportionately will not be affected as much as a lighter bike will. We can get into this one more if you want, but let's deal with the other stuff first.

    Are you forgetting that a heavier object takes more energy to move (over a bump for example) so it will loose more velocity going over that bump than a lighter object?

    Your example of rolling objects isnít really fair as a bowling ball is much larger than a pool ball, so itíll be able to roll over your had so much easier.

    Take a ping pong ball and a lead ball the size of a ping pong ball and roll them both into a pen at various speeds. At some point the ping pong ball will be able to bounce over but lead ball wonít.

    So in summary, given two bikes that are identical except for the frame (one bike is heavier), provided you tune the suspension to account for the extra static load (note the static load includes the rider and sprung mass of the bike), both bikes will transfer the same about of movement to the rider. If the suspension bottoms, then the bikes behave as rigid bikes and the laws of conservation of momentum take over.

    If you have a 40lb bike and a 30lb bike traveling at the same speed, the 40lb bike will have more potential energy, but it will also loose more of that energy when it rolls over a bump due to its extra mass (it takes more energy to lift up a larger object). And donít forget that it takes more energy to get the heavier bike traveling at the same speed as the lighter bike in the first place.

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    The mass of a bike is not that important what is important is the mass of a front wheel, fork, stem and handlebars as compared to whole mass of a bike nad rider.
    In a rock garden you are not hiting rocks perfectly in their middle, you hit them at an angle, so the force will try to turn your handlebars. The lighter handlebars as compared to the mass of a bike and rider will be more likely to turn, not lift up the whole bike with rider.
    Also the statement that ground does not move is false. Rocks do move, there are loose in rock gardens !! I've seen rocks size of a 4 human fists geting 3 meters in the air after a 25lbs bike comes at speed over them. Why heavier bike will bounce less in that situation in obvious.

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    Quote Originally Posted by Michal
    ...... compared to whole mass of a bike nad rider.
    Yeah, big nad's help you go faster.

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    Quote Originally Posted by Michal
    The mass of a bike is not that important what is important is the mass of a front wheel, fork, stem and handlebars as compared to whole mass of a bike nad rider.
    In a rock garden you are not hiting rocks perfectly in their middle, you hit them at an angle, so the force will try to turn your handlebars. The lighter handlebars as compared to the mass of a bike and rider will be more likely to turn, not lift up the whole bike with rider.
    I don't see how mass of the handlebar will provide much resistance to front tire deflection. And how does the mass of the front end of the bike help it to have a supple back end? The performance of the rear suspension is nearly as important when examining the overall ride of a bike in rough terrain, isn't it?


    Quote Originally Posted by Michal
    Also the statement that ground does not move is false. Rocks do move, there are loose in rock gardens !! I've seen rocks size of a 4 human fists geting 3 meters in the air after a 25lbs bike comes at speed over them. Why heavier bike will bounce less in that situation in obvious.
    It's obvious? This is essentially what we've been discussing. Would you care to elaborate?

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    Quote Originally Posted by sliderhouserules
    I don't see how mass of the handlebar will provide much resistance to front tire deflection. And how does the mass of the front end of the bike help it to have a supple back end?
    Not to speak for Michal, but I'm assuming that he's talking about the extra inertial resistance against front wheel deflection. The extra gyroscopic effect of a heavier wheel would be significant, but I agree with you that a couple of 100 grams of bar and stem ain't going to feel that different. Mainly because the handle bars are attached to your arms and body which have much more mass.

    A much better solution for resisting front wheel deflection is a steering damper. I have one on my XC bike and I'll be getting another one for my DH bike for next season.

    Check em' out at http://www.hopey.org/

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    Quote Originally Posted by sliderhouserules
    I don't see how mass of the handlebar will provide much resistance to front tire deflection. And how does the mass of the front end of the bike help it to have a supple back end? The performance of the rear suspension is nearly as important when examining the overall ride of a bike in rough terrain, isn't it?
    Imagine a bike comming at rock at an angle so the hit will try to deflect handlebars and lift the front end the same time. Now imagin that the bike is 2x heavier (all parts of a bike are 2x heavier), now the steering part of a bike (wheel, fork, handlebars, stem) need 2x the energy to be deflected the same way, but since the bike have to be lifted with the rider, just a little more energy will be needed to lift the bikes front end over the rock. The conclusion is that wheel, fork, handlebars and stem will be deflected much less in the second case.
    The giroscopic effect is another issue.

    Quote Originally Posted by sliderhouserules
    It's obvious? This is essentially what we've been discussing. Would you care to elaborate?
    Yes it is obvious that heavy steering part of the bike will be deflected much less than light one when going over loose rocks.

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    Quote Originally Posted by Steve71
    ...
    Check em' out at http://www.hopey.org/
    Link doesn't work. What are these? I've never heard of them.

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    Quote Originally Posted by Michal
    Imagine a bike comming at rock at an angle so the hit will try to deflect handlebars and lift the front end the same time. Now imagin that the bike is 2x heavier (all parts of a bike are 2x heavier), now the steering part of a bike (wheel, fork, handlebars, stem) need 2x the energy to be deflected the same way, but since the bike have to be lifted with the rider, just a little more energy will be needed to lift the bikes front end over the rock. The conclusion is that wheel, fork, handlebars and stem will be deflected much less in the second case.
    I understand deflection well enough. When you're dealing with the mechanics of rotational motion things change quite a bit, though. The mass of a stem is going to have very, very little effect on front tire deflection. Nearly all of its mass is at the center of rotation so movement from (of) the front tire will result in travel on the order of centimeters for most of the stem. The fork is in the same category, maybe even moreso. The greater portion of the handlebars as well, so you're left with maybe six inches on each end of the handlebars that are far enough from the center of rotation to really make some kind of a difference. Such little volume of handlebar material is also going to make a miniscule difference.

    Now if you attached five pound weights on each end of your handlebars then it would help resist front tire deflection, but it would make the bike pretty unwieldy.


    Quote Originally Posted by Michal
    The giroscopic effect is another issue.
    I think the majority of tire/wheel weight falls into the same category as the other stuff above (IE it has little effect resisting rotational motion) until you consider that gyroscopic forces again have very different dynamics.


    Quote Originally Posted by Michal
    Yes it is obvious that heavy steering part of the bike will be deflected much less than light one when going over loose rocks.
    This may have some merit, but not so much when you consider the bike as a whole and remember that we're talking about rear suspension also. Does less front tire deflection help the back end to absorb bumps better?


    I don't have time to respond to your large post, Steve71, but stay tuned...

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    Quote Originally Posted by sliderhouserules
    Link doesn't work. What are these? I've never heard of them.
    Link works for me

    The Hopey steering damper sits in your steerer tube and dampens handle bar movement away from center, but not back to center. In a nut shell it stabilizes your steering.

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    Quote Originally Posted by sliderhouserules
    I understand deflection well enough. When you're dealing with the mechanics of rotational motion things change quite a bit, though. The mass of a stem is going to have very, very little effect on front tire deflection. Nearly all of its mass is at the center of rotation so movement from (of) the front tire will result in travel on the order of centimeters for most of the stem. The fork is in the same category, maybe even moreso. The greater portion of the handlebars as well, so you're left with maybe six inches on each end of the handlebars that are far enough from the center of rotation to really make some kind of a difference. Such little volume of handlebar material is also going to make a miniscule difference.

    Now if you attached five pound weights on each end of your handlebars then it would help resist front tire deflection, but it would make the bike pretty unwieldy.



    I think the majority of tire/wheel weight falls into the same category as the other stuff above (IE it has little effect resisting rotational motion) until you consider that gyroscopic forces again have very different dynamics.



    This may have some merit, but not so much when you consider the bike as a whole and remember that we're talking about rear suspension also. Does less front tire deflection help the back end to absorb bumps better?


    I don't have time to respond to your large post, Steve71, but stay tuned...
    I'll put this another way. The crappy heavier bike was a better descender. The effects i described are most importend in understaning why it was the case.

    Simple example

    assume that rock does not move, and the velocity of bike is constant in this 2 examples

    rider weight - 100kg
    bike weight -10 kg (including 3kg for steering part, weight distribution is importand, but not for this example)

    hiting a rock at an angle will generate a deflecting force at a wheel, and a lifting force at a whole bike with a rider

    rider weight - 100kg
    bike weight 13kg (including 6kg for steering part, the distribution of this mass is proportional to the example above)

    total force (the same velocity) will be 113/110 - < 3% greater in first example, jet the steering part is 2x heavier, so it will deflect almost 2x less (not the whole bike with rider deflects, but only its steering part)!, the bike will be going over rocks and will not bounce around due to front wheel deflecting (the arms will try to damp this deflection, but it does not compensate for movment perfectly)

    now the rear wheel, it will bouce less becouse rocke that the bike is going over are loose, and their mass is much lower than the mass of a bike, it may seem that the extra weight of a bike in this case should not make a great diffrence, but when we take into account that in rocky descent you are using your legs as a suspension than the proportions change

    some other effects will help the heavier bike like, gyroscopic effec, or lover center of gravity, or possibly better vibration dampening (steel), but those effects are less importand

    PS
    sorry for spelling mistakes, but the online dictionary i always use to translate some of the words is offline

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    ... and if we just ... But try wally bike vs a DH rig!!!

    I don't know much about the guy's Ibis bike but lets assume were talking about going downhill and not up, as that is where the offence in question occured. A guy said earlier that the Ibis has a riding position geared towards smooth flat/uphill trails and maybe not so much dh so I'm guessing its an XC style bike. This wally thing has god knows what kind of geometry but try pitting it against a Kona Stab or something like that and see who gets to the bottom quickest and in one piece. Basically if you were hacking down a proper DH course on some £200 full suspension bike and you hit a football-sized rock head on it wouldn't surprise me if the fork snapped and you broke your face on a tree....a £2500 DH bike, on the other hand, would take it on and give just you a fresh dose of adrenaline to play with.

    Personally, I have built my hardtail up to be worth around £1000 and it is fantastic on smooth rolling trails and uphill sections but man what I would give for some rear bounce coming down...I mean my fingers are killing me as we speak from a ride a couple of days ago (possibly to do with crappy grips which will be replaced very soon), but for my own safety and long term enjoyment of the sport, there is no way I'm going out and buying a cheap and nasty full suspension bike. I'll save up £2000, knacker my body in the meantime, but eventually own a machine which will allow me to fly downhill at a speed that should I encounter someone on a "Wally World" bike, I am confident I will eat him for breakfast (in a sensible, trail-etiquette abiding manner).

    Enjoy the discussion...I am

    Kev

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    Quote Originally Posted by Steve71
    Not to be rude, but since it wasnít a controlled experiment, ltripper experience is anecdotal. But this discussion is now more about, ďis a bike with a heavier frame faster due to itís extra mass?Ē
    Being faster is only part of the overall picture. I think it's important to keep the context of the Walmart bike vs. the Ibis bike because that's what I've been trying to figure out. The important thing that stood out to me when I read Itripper's post was that the Walmart bike held its ground so well from a suspension performance perspective. The Ibis bike seemed to be beating the hell out of the rider while the Walmart bike made it feel like there weren't any bumps in the trail at all, so to say. I started trying to figure out why that would be.

    For me the question would be more like "Is a bike with a heavier frame able to absorb bumps better?" Or maybe "What are the most important factors that enable one bike to handle rough terrain better than another bike?"

    Quote Originally Posted by Steve71
    Quote Originally Posted by sliderhouserules
    What's involved in "suspension"?
    I like to think of the two facets of a suspension system as shock absorption and rebound damping.
    ...
    I donít really agree with that. The components that make up a suspension system and effect itís performance are

    (1) Travel
    (2) Rebound damping
    (3) Compression damping
    (4) Spring rate
    (5) Un-sprung mass
    (6) Static load

    Looking at the bikes ability to absorb a single impact isnít going to tell you much about its ability to handle a rock garden (which requires well tuned rebound damping).
    I was trying to simplify it as much as possible. When a suspension system performs what is it actually doing? It is providing shock absorption (compression damping) and then it is rebounding, which is typically dampened. The first factor there is essentially the raw performance of the overall system. How well can it take a hit? The second factor, on the other hand, is really just something that affects the system's ability to perform the first factor. The things in your list are components of a suspension system, but they are not part of what a suspension system does. I should have worded my stuff a bit differently to give that context more clearly.


    Quote Originally Posted by Steve71
    I donít agree with the weight being the single most important factor. Damping, suspension travel & design, geometry, damping, frame/fork/wheel rigidity and tires (and tire pressure) are all going to come before the weight of the frame.
    I don't think I've been convincing in anything I've said so far in this thread if you can honestly say that you think tire pressure has more effect on suspension performance than the weight of the frame.

    Let's look at your list in the context of the question I framed above:

    "What are the most important factors that enable one bike to handle rough terrain better than another bike?"

    Damping
    I'm assuming you mean compression damping? I'd have to say this belongs at the top of the list. I'd also have to say good compression damping could make up for everything but horrible lack in all the following items in your list, ergo all my previous words in this thread.

    Did the Ibis bike have good compression damping? Who buys a titanium frame and puts crappy shocks on it? I think it's safe to say the Ibis bike had good compression damping. I also think it's safe to say the Walmart bike had good compression damping, otherwise you'd have to take this item off the list, because the Walmart bike apparently took the hits well enough that the riders felt a cushy ride.

    Compression damping is the key factor.

    Suspension travel & design
    This should really be separated because these two dymanics affect the system in different ways. Travel does have good merit in this discussion, and I've purposely ignored it, as I have other factors that I think also play a part, choosing to focus on the one thing I think tops the list. So don't think I'm trying to say these other things aren't playing a part. Amount of travel certainly does play a part. Seven inches of travel is going to perform better than three inches of travel. I think once you get up to four inches of travel, though, you're going to see pretty comparable performance on most terrain other than drops and very large hits. More travel can actually be a disadvantage if you have it set up for terrain other than what you're riding.

    For illustration, I have a TALAS fork on my bike, with adjustable travel. If I crank down 10mm of the travel for a climb and then forget to let it back out before I go back down, I generally don't notice too much difference. Now if I crank down all 40mm of travel that I can then I will notice a difference, but 85mm (the minimum it can go) is 3.3 inches. When you're down at 3 inches of travel the bike acts too much like a rigid bike for anything but small bumps, I think.

    Suspension design (part 2 of this item) is pretty minimal. I spent a lot of time researching suspension designs before I bought my new bike at the first of summer. Front suspension designs don't have any differences worth talking about here, unless you want to get into the merits of coil vs. air. But my TALAS is an air-sprung fork and my bike is a downhill dream as far as I'm concerned, so I'll respectfully decline the merits of any such discussion. Rear suspension design, as long as it's one of the accepted designs worth buying, is mainly different on the points of pedal- and brake-jack. (Spend any amount of time reading up on it on these forums and I'm sure you'll come to the same conclusion.)

    I think we also have to assume the Walmart bike has a (passably) good suspension design, otherwise this whole item has to go off the list as well.

    Geometry
    This is another factor that I've chosen to ignore even though it keeps standing out in the back of my mind. If I knew the comparative geometries of the Ibis bike and the Walmart bike I might be arguing this one as top item... I keep relegating it down the list, though, due to the half (or nearly half) of the equation that consists of the back end. What can you analyze about rear end geometry? Rear wheel travel path during compression? That would qualify as suspension design, and will have more effect on pedal- and brake-jack, as I've mentioned. It will also have effect on how much a bike is slowed down by frontal impacts, but that's a different look, and I talk about that concept a bit later. I don't think it affects suspension performance.

    Damping [again...]
    You sure like damping. Rebound damping this time? You've pretty resoundingly thrown out my attempts to reduce this analysis to talking about how the bikes can handle a single bump rather than worrying about repeated bump performance. But, this item, and a couple of the other ones that are minor, are the only things that come much into play when you look at repeated bumps rather than a single bump. As I said before, I think the rebound damping performance of a bike has impact limited to making the compression damping more or less efficient.

    What else does it really do? (Skipping will actually allow a bike to get a bit more speed, if you believe my free-fall stuff I postulated earlier. )

    Frame/fork/wheel rigidity
    I think the frame's ability to damp vibration is something that's more noticable over longer periods, and has not much to do with the facets of raw suspension performance we're looking at.

    Fork and wheel rigidity fall under front tire deflection which is probably better analyzed as a whole. Michal has brought that into the discussion fully so maybe we can look at his points in context.

    Tires (and tire pressure)
    Hmm... unless you're talking the difference between a flat tire and one inflated so much that it's hard, I think the centimeter or two (max) of travel afforded by tire compression is pretty minimal. Tire pressure can affect grip to a great degree, and it can affect whether you get flats on rough terrain. Do you really think it affects suspension performance all that much?

    You may be inferring tire/wheel weight in here. If so I think it needs to be lumped into the category above of rebound damping... I argued against it there.


    Quote Originally Posted by Steve71
    What you say is correct, but incomplete. If youíre going to compare apples to apples, you would need a slightly lighter spring in the case of the lighter frame. So then both bikes would respond exactly the same to the same upward impact from the fork (unless the fork bottoms Ė then it will act as a ridged bike), given the same static load (the rider). You canít compare the suspension performance of two bikes unless they have the same amount of sag.

    Thatís why you can have the same suspension performance from a bike with a 150lb rider and a 200lb rider. You adjust the spring. In your example, youíre not adjusting the spring to compensate for the lighter static load.
    The 10 pounds or so of difference in frame weight is not enough to necessitate a spring change, certainly. And the difference in sag is going to be on the order of a millimeter, no? Enough that you can effectively disregard it.

    An apples to apples comparison, and a way to reword what I've already said, would be to take your bike out and run it down a rough descent, taking note of the performance. Then take your same bike and strap 10 pounds to the frame securely and evenly enough that it won't make it unwieldy or fall off or come loose, and then go run the same descent, taking note of the changed performance. You seem so unconvinced by my arguments that I encourage you to do this. I'm going to keep an eye out for something that would allow me to strap 10 pounds of weight to my frame so that I can do this experiment myself. I've been basing my positions off riding different bikes of different weights, but this would be the best way to make sure I know what I'm talking about.

    An alternative would be to carry the 10 pounds on your back for the first run, then strap it to your bike the second run. Though that will change your feel, and gauging the feel of the rider is really the whole experiment, so it might be good to do it both ways...


    Quote Originally Posted by Steve71
    ...extra frame weight is a hindrance anyway (provided it doesnít add stiffness).
    ...
    Are you forgetting that a heavier object takes more energy to move (over a bump for example) so it will loose more velocity going over that bump than a lighter object?
    ...
    If you have a 40lb bike and a 30lb bike traveling at the same speed, the 40lb bike will have more potential energy, but it will also loose more of that energy when it rolls over a bump due to its extra mass (it takes more energy to lift up a larger object). And donít forget that it takes more energy to get the heavier bike traveling at the same speed as the lighter bike in the first place.
    My whole point in bringing this up is that the heavier object, since we're talking about suspended systems, will not be deflected as much by the same terrain objects at the same speed. The analysis changes completely when you allow this factor into the equation. Chances are the heavier (suspended) object will lose the same or less energy, and since it starts with a larger pool of energy, losing even the same amount of energy will result in less effect (IE slow it down less) because it's proportional.


    Quote Originally Posted by Steve71
    Your example of rolling objects isnít really fair as a bowling ball is much larger than a pool ball, so itíll be able to roll over your had so much easier.

    Take a ping pong ball and a lead ball the size of a ping pong ball and roll them both into a pen at various speeds. At some point the ping pong ball will be able to bounce over but lead ball wonít.
    Let me try this again with a better example. Have you seen the new movie Dodgeball? If not, just imagine a good size bouncy ball. Roll that down a rough incline, rough enough to impede the ball. Now imagine being able to attach a 10 pound weight inside the ball in such a way that it stays in the center when the ball bounces, and it doesn't affect the "bounciness" of the ball much if at all. Now roll this heavy ball down the same rough incline and watch how it just soaks up the bumps instead of bouncing off them. It will retain its speed better because it won't bounce off the terrain as much as the lighter ball will. Some of the bounces of the lighter ball will actually be in the opposite direction of its downward movement. Will the heavy ball ever be bounced directly uphill? No. When you look at extremes like this it helps you see how objects in the middle will act. They'll just not be so pronounced.


    Quote Originally Posted by Steve71
    So in summary, given two bikes that are identical except for the frame (one bike is heavier), provided you tune the suspension to account for the extra static load (note the static load includes the rider and sprung mass of the bike), both bikes will transfer the same about of movement to the rider.
    I think you're taking a leap here. Let's say I have a typical 30 pound mtn bike and a bike that weighs 250 pounds, both bikes having identical suspension designs, geometry, and rider, with the spring rates adjusted for sag and unsprung weight. The 250 pound bike is going to transfer the same movement to the rider when it travels over a bump? I don't think so. The 250 pound bike is barely going to move vertically at all -- at all -- when it hits a bump.

    You should try the brick-in-the-hand experiment. Hold a brick in one hand and hit it with a hammer with the other hand. Now switch and do the same with a 2x4 of the same length as the brick. Simple experiment and it will easily show you most of what I've been talking about.

    I'm late now... argh! GF is going to kill me.

    Later.

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    Quote Originally Posted by sliderhouserules
    You should try the brick-in-the-hand experiment. Hold a brick in one hand and hit it with a hammer with the other hand. Now switch and do the same with a 2x4 of the same length as the brick. Simple experiment and it will easily show you most of what I've been talking about.
    Iíve agreed with you on this all along . I even provided a link to the formulas for conservation of momentum in an earlier post in this thread. But what your example of two solid objects (of some what similar mass) hitting one another has to do with what were examining here totally eludes me .

    Itís as simple as this;

    Either the suspension bottoms or the suspension does it job.

    If the suspension bottoms, then we have a 40lb object hitting a massively heavy object (the earth) vs. a 30lb object hitting a massively heavy object. Not two solid objects (of some what similar mass) hitting one another.

    In the case were the suspension does its job then we donít have one solid object hitting another solid object. We have a device in-between (suspension), which, as you mention earlier, converts energy into heat. The laws of conservation of momentum donít apply.

    Quote Originally Posted by Steve71
    So in summary, given two bikes that are identical except for the frame (one bike is heavier), provided you tune the suspension to account for the extra static load (note the static load includes the rider and sprung mass of the bike), both bikes will transfer the same about of movement to the rider.
    Quote Originally Posted by sliderhouserules
    I think you're taking a leap here. Let's say I have a typical 30 pound mtn bike and a bike that weighs 250 pounds, both bikes having identical suspension designs, geometry, and rider, with the spring rates adjusted for sag and unsprung weight. The 250 pound bike is going to transfer the same movement to the rider when it travels over a bump? I don't think so. The 250 pound bike is barely going to move vertically at all -- at all -- when it hits a bump.
    The laws of physics are disagreeing with you here . Provided neither bike bottoms out, and both bikes have the spring rate adjusted such that they have the same sag, then they will both see the same forces at the pedals, seat and handle bars after they hit a bump. Thatís a fact.

    Otherwise suspension performance would vary wildly depending on rider weight. Which is not the case provided you run the correct spring.

    Static load (sprung mass) is not something you add to a suspension design to increase itís ability to absorb shock. But rather something you take into consideration when calculating the spring rate. Once again this is fact, not opinion.

    But hey, Iím totally willing to eat my words here if you can provide hard evidence to the contrary.

    Quote Originally Posted by sliderhouserules
    Let me try this again with a better example. Have you seen the new movie Dodgeball? If not, just imagine a good size bouncy ball. Roll that down a rough incline, rough enough to impede the ball. Now imagine being able to attach a 10 pound weight inside the ball in such a way that it stays in the center when the ball bounces, and it doesn't affect the "bounciness" of the ball much if at all. Now roll this heavy ball down the same rough incline and watch how it just soaks up the bumps instead of bouncing off them.
    So here we have foam ball, which is a crude spring/damper system (elastomers anyone? )

    Whether or not the extra 10 pounds added the center of the ball would help it absorb shock really depends on the spring rate of the foam.

    So, once again, in your example, youíre forgetting to correct the spring rate (of the foam) to compensate for the extra static 10lb load. If the ball was made out of really really soft foam then the 10lb of mass would compress it so much that the ball wouldnít roll and would bottom against the rocks and roots as it rolled down the trail, but a 2 lb mass added to the ball would not compress the foam much and allow it to conform to the terrain.

    Quote Originally Posted by Steve71

    What you say is correct, but incomplete. If youíre going to compare apples to apples, you would need a slightly lighter spring in the case of the lighter frame. So then both bikes would respond exactly the same to the same upward impact from the fork (unless the fork bottoms Ė then it will act as a ridged bike), given the same static load (the rider). You canít compare the suspension performance of two bikes unless they have the same amount of sag.

    Thatís why you can have the same suspension performance from a bike with a 150lb rider and a 200lb rider. You adjust the spring. In your example, youíre not adjusting the spring to compensate for the lighter static load.

    Quote Originally Posted by sliderhouserules
    The 10 pounds or so of difference in frame weight is not enough to necessitate a spring change, certainly. And the difference in sag is going to be on the order of a millimeter, no? Enough that you can effectively disregard it.
    Exactly, 10lb is not going to make much difference, I only brought it up to demonstrate how your example (see quote below) is incorrect/incomplete as you havenít taken into account a spring rate change for the extra load. But as you say it would be fairly insignificant anyway, so I donít see why you even brought it up (it seems that itís the basis for your whole line of reasoning though )

    Quote Originally Posted by sliderhouserules
    When the spring exerts a force against the upper object (the frame) that object on the other end (the frame) is going to resist that force with its inertial mass. Heavier objects have more inertial mass. If the object has a high enough inertial mass the spring will be caused to compress. If it has a low enough inertial mass the spring won't need to compress because the object will move. Even if one object (frame) is only slightly heavier than another object (frame) it will have a higher inertial mass to resist that force with, and will therefore cause the springs to have to absorb more of the force or movement (even just a little bit).

    A heavier frame will not be moved as much as a lighter frame. If you can agree with this I'm not sure why the argument needs to go any further. There are other considerations, but this is the main point. This is a fairly complete look at the physics involved.

    Quote Originally Posted by sliderhouserules
    An apples to apples comparison, and a way to reword what I've already said, would be to take your bike out and run it down a rough descent, taking note of the performance. Then take your same bike and strap 10 pounds to the frame securely and evenly enough that it won't make it unwieldy or fall off or come loose, and then go run the same descent, taking note of the changed performance. You seem so unconvinced by my arguments that I encourage you to do this
    All your doing is adding 10lb of static load. If you change the spring rate to compensate, then the bikeís suspension will perform exactly the same.

    Any benefit you get from adding extra mass, without changing the spring rate, just means you were running an over sprung bike in the first place. The extra 10lb of mass is going to he harder to turn, accelerate and stop though. It makeís much more sense to run the correct spring rate in the first place, rather than using a band-aid approach.
    Last edited by Steve71; 07-06-2004 at 03:28 PM.

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    Steve71, I don't think you've agreed with or built upon a single point I've made in the context of what I've been trying to answer in this thread. So... I'd like to hear your answer to why the Walmart bike rode better than the Ibis, but without trying to answer, counter or rebut anything I've said in this thread. I still haven't seen you do that.

    Why did the Walmart bike ride better than the Ibis?

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    Itripper, if you're still reading this thread, you've probably got some answer to this. Why do you think the Walmart bike rode better than your Ibis?

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    Quote Originally Posted by sliderhouserules
    Steve71, I don't think you've agreed with or built upon a single point I've made in the context of what I've been trying to answer in this thread.
    Why did the Walmart bike ride better than the Ibis?
    I guess it could appear that I'm just being disagreeable or something, but what you were saying just didn't add up when you applied it to our example. In the last couple of posts I think we found out where we were disagreeing, but for the first 3 or 4 post I don't think we were even talking about the same aspect of the problem .

    All in all though it was an enjoyable discussion. You really made me think hard about my conclusions about the pro's and con's of extra frame mass.

    Quote Originally Posted by sliderhouserules
    So... I'd like to hear your answer to why the Walmart bike rode better than the Ibis, but without trying to answer, counter or rebut anything I've said in this thread. I still haven't seen you do that.
    In the end the discussion focused simply of frame weight and the idea that it may/may not provide resistance to compression (as you suggested). But to address the original questionÖ..

    As I said before, ltripper experience is largely anecdotal as it wasnít a controlled experiment. Off hand, here are a few questions we would need to answer before we could make an informed opinion about why the wally was/wasnít better.

    (1) Suspension travel - how much travel did the wally bike have?
    (2) What range of impacts was itís suspension tuned for? Was the suspension using 4 inches of travel over the rocks? Would it bottom on a little jump? Would it pedal like a slug because itís suspension was setup so soft?

    (3) Was the wally bike running the correct sag for the riders weights?
    (4) How large a volume were the wallyís tires?
    (5) What tire pressure was the wally running?
    (6) What was the HA of the wally?
    (7) Stiffness! Was the wally a stiffer bike (frame/fork/wheels).

    Off hand the wallyís wheel and tire weight would help stabilize the bike due to the gyroscopic effect. But apart from that what else has it go going for it? Maybe suspension travel?

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    There are a couple of important points that I believe Steve has been trying to point out, but aren't getting across.

    1) The mass of the bike and rider are negligible compared to the mass of the bump and attached PLANET. Lets neglect suspension for a minute here. If a wheel is heading towards a bump, three things can happen: a) the wheel, and whatever is attached to it, accelerate upward and move up over the bump, or b) the wheel keeps on going straight, and the bump, and whatever is attached to it (the Earth) move down, or c) There is a collision and the wheel stops. I realize some loose bumps can move, but generally speaking they donít. Lets say our bump is a bedrock lip. OKÖwe all know ďbĒ isnít going to happen. The wheel will move over the bump, of course. People keep saying the heavier the mass of the wheel and whatever is attached to it, the more itíll resist moving. Well, the path the wheel must take to get over the bump is FIXED. The ground is not getting out of the way, so the wheel must move over the bump, regardless of its mass. Now, here is where I think some of you are getting confused- the greater the mass of the wheel/bike, the GREATER THE FORCE THE BUMP WILL APPLY TO THE WHEEL! It simply MUST happen if choices ďbĒ or ďcĒ donít occur. The Bump will keep applying greater and greater force until the wheel moves a sufficient amount to go over the bump. The mass of the wheel/bike IS resisting moving, but a greater force to overcome that resistance is simultaneously being applied to the wheel by the bump.

    Now, when we feel a bump, the amplitude of the move isnít generally what hurts us- it is the acceleration. Two completely rigid bikes moving the same speed over the same bump must take the same path to clear the bump. The force applied to move the light bike will be applied over the same period of time as the (greater) force applied to move the heavy bike, so the bump will feel the same. The forces will be of a magnitude to impart the same acceleration on either bike (rigid body with elastic collisions assumptions)

    Suspension, of course, changes things. The wheel will be accelerated over the bump the same as before, but now the mass is sprung. How quickly the mass is accelerated over this bump depends on how massive it is, the spring rate suspending it, and how much travel there is. If two bikes have identical amounts of travel, but one has 100 pounds supported by that wheel and a 100 lb/in spring rate, and the other has 150 lbs supported by the wheel and a 150 lb/in spring rate, they should both accelerate upward over the bump at the same rate. If you put the 100 lb/in spring under the 150 lb mass, the spring will need to compress 50% further to supply the force needed to lift the larger mass. This will take more time, and will lift the mass up over the bump more gradually. This will result in a smoother ride AS LONG AS YOU DONíT BOTTOM OUT. Bottoming out will cause an acceleration spike for the rest of the bump just as strong as if you had no suspension at all, except shorter in duration. This is BAD. If you are 50% under sprung, the ride will be very smooth as long as you donít bottom, but you will be bottoming much more often- unless you add more travel.

    2) A major point many of you are neglecting is TOTAL sprung mass. Sure- If a Superlight weighs 5.5 pounds, and a Bullit frame weighs 8.5 pounds, the Bullit weighs about 55% more. If all the other parts are proportionally bigger on the Bullit, the total sprung mass may be 55% greater and youíll have a 37 pound bike vs a 24 pound bike. But put a 175 pound rider on with 10 pounds of water, tools, and clothes on either bike and lets look at the numbers again. (Lets assume the riders butt is firmly on the seat, and he isnít suspending himself with his knees and elbows)

    185+24= 209
    185+37= 222

    222/209=1.06.

    Thus, the total sprung mass of the Bullit is only 6% greater than the total sprung mass of the Superlight! This isnít enough of a difference to account for the results you guys are claiming.

    As to why the ibis was beat by the beater, Iím not sure. Cheap bikes tend to have little to no damping. Perhaps this was just the setup for the high frequency these bumps were likely at, and perhaps the bumps were just small enough to not bottom the Mongooseís suspension. Maybe the Ibis was running too much rebound damping for this trail, and the suspension packed in and made it into a rigid bike. Also, perhaps the Ibis was a hardtail.

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    When I was like.. 11, 12 years old I had this Wal * Mart Special. Some POS with "full suspension" Now this thing rode like a dream, so I guess it wasnt a POS. Everything on it was smooth, however, it was extremely heavy. I used to take it on some dirt hills thinking I was a hardcore biker (naturally, I held the brakes all the way lol) and then I out grew it and let it rust in the rain

    Point being that some bikes might suprise ya

    -levi

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    Quote Originally Posted by @dam
    There are a couple of important points that I believe Steve has been trying to point out, but aren't getting across.
    I think I've understood, at least to some degree, every point that Steve has made. I've tried to speak to every point, but don't think that my points were well understood because we've ended up arguing the same positions again and again. Since his arguments are just counters to my points there isn't much room to respond in any way other than to try to re-explain my point(s). I've asked him to take a different approach and give an answer to what we're wondering about rather than rebut my points, but the response to that is "I don't know".


    Quote Originally Posted by @dam
    1) The mass of the bike and rider are negligible compared to the mass of the bump and attached PLANET. Lets neglect suspension for a minute here.
    ...
    Well, the path the wheel must take to get over the bump is FIXED.
    Steve has brought this point up many times. It ultimately has zero significance because we aren't looking at what rigid bikes do when they hit a bump. No one can mistake that the ground isn't going to be the one that moves when a bike encounters a bump. So the only merit this whole line of thinking has is to demonstrate that when a bike hits a bump there is a force exerted upwards against the tires of the bike. Since my entire line of thinking grows out from this single point I find myself wondering why it keeps coming up...


    Quote Originally Posted by @dam
    The ground is not getting out of the way, so the wheel must move over the bump, regardless of its mass. Now, here is where I think some of you are getting confused- the greater the mass of the wheel/bike, the GREATER THE FORCE THE BUMP WILL APPLY TO THE WHEEL!
    ...
    Suspension, of course, changes things...
    This is again the same point from a different angle. The ground exerts a force upwards against the bike, yadda yadda. We're not looking at rigid bikes so we have to consider the effects of suspension from the start. When you have a suspension system the entire dynamic changes including the amount of force exerted by the ground upwards against the bike.


    Quote Originally Posted by @dam
    The wheel will be accelerated over the bump the same as before, but now the mass is sprung. How quickly the mass is accelerated over this bump depends on how massive it is, the spring rate suspending it, and how much travel there is.
    ...
    ...the spring will need to compress 50% further to supply the force needed to lift the larger mass. This will take more time, and will lift the mass up over the bump more gradually.
    You have the gist of my argument here, yet you're arguing against it in your second (2) point below -- ???


    Quote Originally Posted by @dam
    This will result in a smoother ride AS LONG AS YOU DON?T BOTTOM OUT.
    Itripper never mentioned bottoming out, but this is informative .


    Quote Originally Posted by @dam
    2) A major point many of you are neglecting is TOTAL sprung mass.
    I hope you aren't including me in your "many" because I've talked about this quite thoroughly. I even did the nifty graphics to demonstrate this in detail.

    The entire Heavier Frame = Smoother Ride argument can be summarized by saying the entire system of a person riding a fully suspended bike is actually two suspension systems: the bike's suspension, and the suspension provided by the arms and legs (and other body motions) of the rider. When the lower suspension is caused to compress by the force of a bump it may or may not be able to absorb the entire force of that bump all by itself. If you can concede that the lower suspension systems of both bikes are capably efficient (I don't know much about Ibis bikes, but Itripper inferred that it's a quality bike, and the Walmart bike should not have been able to out-perform it... yet it did so we have to assume the Walmart bike is capable, also) then you can transpose this same problem onto a simpler system, which is what my graphics were intended to represent. Examining that system using basic Newtonian physics we can clearly see that the mass of the inner suspended object (which represents the bike frame) will have a noticeable effect on the amount of force that is subsequently transferred to the upper suspension system (which represents the rider's arms and legs) when the lower sub-system receives an upward impact force. When you have a 50% difference in the mass of that middle object that is not neglible. In fact, force equations for springs are linear, so it relates directly -- a 50% change in mass of the middle object means it will transfer 50% more/less force to the upper system.

    The root question is "why did the Walmart bike feel softer than the Ibis?" In other words, why did the Walmart bike transfer less of the force of bump impact to the rider? That has nothing to do with total sprung weight (aside from the sag adjustment issue(s) that Steve brought up which I think are inconsequential).


    Quote Originally Posted by @dam
    As to why the ibis was beat by the beater, I?m not sure. Cheap bikes tend to have little to no damping. Perhaps this was just the setup for the high frequency these bumps were likely at, and perhaps the bumps were just small enough to not bottom the Mongoose?s suspension. Maybe the Ibis was running too much rebound damping for this trail, and the suspension packed in and made it into a rigid bike. Also, perhaps the Ibis was a hardtail.
    The rebound damping question has a lot of merit, but unfortunately can only be answered by Itripper... Your thoughts are well-reasoned, though. Thanks for joining in.

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    So, what your saying..........

    Is that the biggest factor in suspension performance is the weight of the bike. The frame in particular. Sure makes all of these fancy oil damped and air sprung forks seem like a waste then. If I want my fork to work better, I should just get a heavier bike. Or at least put some sandbags on the frame that I have.

    But seriusly, maybe the Ibis is not the best suspension bike to make this comparison on. The Ti suspension bikes have been known to be a bit on the flexy side. This could create all kinds of weird handling while crossing a boulder field. It would be interesting though to put the Wal-Mart bike up against an AL bike. Maybe we could pit it against a Giant AC1 and an NRS1 too. Then we could see how that bike handles against multiple FS designs, and with bikes at different weights. My suspicion is that the AC would come out the best even though it probably weighs less than the Wal-Mart bike.

    Also, the OP did not say that they were going downhill. He said that they were going "down the trail". So a heavier bike would not be an advantage while traversing flat (albeit rough) terrain. Therefore, keeping the tires, particularly the rear, in contact with the ground should have a positive effect on the velocity one could maintain. Of course, learning how to 'float' over the rough stuff would help the rider on a lighter bike to maintain momemtum. The rider on the heavier bike cam simply plow into things and let the extra inirtia carry them through
    "There are those who would say there's something pathological about the need to ride, and they're probably on to something. I'd wager though that most of the society-approved compulsions leave deeper scars in the psyche than a need to go and ride a bicycle on a mountain." Cam McRea

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    Let me repeat myself real quick...

    How quickly the mass is accelerated over this bump depends on how massive it is, the spring rate suspending it, and how much travel there is. If two bikes have identical amounts of travel, but one has 100 pounds supported by that wheel and a 100 lb/in spring rate, and the other has 150 lbs supported by the wheel and a 150 lb/in spring rate, they should both accelerate upward over the bump at the same rate. If you put the 100 lb/in spring under the 150 lb mass, the spring will need to compress 50% further to supply the force needed to lift the larger mass. This will take more time, and will lift the mass up over the bump more gradually. This will result in a smoother ride AS LONG AS YOU DONíT BOTTOM OUT. Bottoming out will cause an acceleration spike for the rest of the bump just as strong as if you had no suspension at all, except shorter in duration. This is BAD. If you are 50% under sprung, the ride will be very smooth as long as you donít bottom, but you will be bottoming much more often- unless you add more travel.
    In your example with your graphic, you merely added more mass to the top of an existing spring. That is not a practical example of what happens on a bike. You could have had the same end result by putting a spring with 1/5 the spring rate under the existing mass as you did by putting 5x the mass on the existing spring. Your point isn't that more mass makes for a smoother ride- it is that an undersprung bike makes for a smoother ride. It does- as long as you have enough travel where you aren't bottoming out all the time.

    Lets take a system with 5" of travel. There is 100 lbs on it, and a spring with a rate of 25 lbs/in. At rest, the system will be SAGGING 4"! Now, lets say the system encounters a 1" high bump. The most force this will exert on the mass is 125. 125/100=1.25. This bump could exert no more than one and a quarter G. Of course, as soon as you hit a bigger bump you are bottoming out and then will have the same acceleration as a rigid bike, which is why bikes arenít undersprung. Now, if that bike has 10Ē of travel, youíll have 6Ē beyond the sag, allowing the spring to gradually apply a force of 250 lbs, for a total acceleration of 2.5 G- or course, you wonít be bottoming out that often either.

    Anyway, my point is you are really saying being undersprung makes for a smoother ride- not that more mass makes for a smoother ride.

  79. #79
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    Snobs

    I have a Mongoose D60R I bought at Costco. It rides well, but my roommate and
    others just thumb their noses at it even though I can outride them. The bike cost
    $300 and came with Rock shock Jett C. I noticed to most of them, it's all about
    the "name" on the parts. I'm sure they think that bike is not a "real bike" since I didn't get it at a LBS.

    I now have a Giant Warp DS-1 w/sram derailer and a Santa Cruz Superlight w/xtr
    components. Great bikes, but I am more confident taking the D60R downhill.

    If you strip the names off the bikes, you are just biking down a hunk of
    aluminum and rubber.

    And about the cheaper wally bikes breaking down, you really don't have proof of that.
    I've not personally seen any catostrophic failure on any cheap bikes. They happen, but
    they also happen on expensive bikes too. Perhaps you have, but I don't
    think these cheap bikes will fall apart instantaneous like you people imply. If you think about it, although cheap, they
    are built on heavy duty steel frames and should outlast aluminum frame. The
    components are another matter.

  80. #80
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    Quote Originally Posted by GaryH
    and came with Rock shock Jett C. If you strip the names off the bikes, you are just biking down a hunk of aluminum and rubber.
    That rock shock jett C fork has what, an elastomer spunge for a damper!?

    It's not just a hunk of alu and rubber. The suspension damping design/performance makes a massive difference in how the bike can handle rough terrain at speed. Just because it's out of sight inside the fork, doesn't mean that isn't not important. Also there are all sorts of grades of alu. Everything from beer cans to aerospace.

    But having said that I agree with you that a cheap bike can be a good bike. I used a $300 kona for years and loved it. Though I did put on a well-damped fork, Z2 Atom bomb, good tires and clipless pedals. I'm taking it to the next level with my Turner though, no question as to which is the better/faster bike. Up or down.

  81. #81
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    8lb difference my A$$

    Sorry, man, 8 lbs is not going to make that big a difference.
    I ride with a guy who weighs 160 and rides a 30-lb bike. I'm 215 and ride a 22lb bike. Doing the math, I have him beat by 47 pounds, and I don't see him flying off any rocks.

    Any chance that maybe, just maybe, it's the rider and not the geometry, tires, shocks, etc.? A strong enough rider could smoke me and my Yeti ARC on a Huffy.

    DrPete

  82. #82
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    Hmmmm...

    Maybe try a light child's plastic ball equal in diameter to a shot-put rolling down a trail and watch the difference.
    Or a playground/soccer/basketball vs a medicine/bowling ball?

    Not much in physics debate to how and why...but I bet there is a difference in their actions.

    Maybe Keith Bontrager can help, he seems to have good discussions of how and why on a few things.

  83. #83
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    I think you guys are misinterpreting each other. The tire will follow the same course over rough ground, yes. But, the heavier bike will resist the suspension transfering the energy to it (the energy doesn't just disappear, the suspension soaks it up unless it bottoms out), and so the frame will follow a different path than the lighter frame. All else the same of course.

  84. #84
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    Quote Originally Posted by Stregone
    But, the heavier bike will resist the suspension transfering the energy to it
    Nope, it's the suspensions spring rate that determines the force transferred to the un-sprung mass.

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    this thread is ridiculous. what's with all the technical garbage?

    obviously, ltripper's brother is a better or more fearless rider. it's that simple.

    to blame it on the bike is ridiculous in the extreme.

    it doesn't matter that ltripper "has been riding for years" or that his Ibis RidiculoSilk was way more expensive or way more refined.

    Steve Peat could beat me to the bottom of the hill on a Big Wheel, I'm sure. No matter what I was riding.

    ltripper needs to get over the fact that his brother has bigger stones. that's all. it's not at all about the bike, nor about the stupid STUPID STUPID attempts to make this into a technical discussion, when it is NOT about bike design or suspension performance.

    maroons.

  86. #86
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    We the people ...

    sell me your beautiful ibis for $200 & buy a high end walmat rig & treat yourself with the change? ;D

    ta

    scant

  87. #87
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    Quote Originally Posted by gonzostrike
    this thread is ridiculous. what's with all the technical garbage?

    obviously, ltripper's brother is a better or more fearless rider. it's that simple.

    Quote Originally Posted by Itripper
    I take his bike down the trail now, with its giant tractor weight tires, and to my disbelief, this heavy tank cheap ass bike, floats down the trail like a caddy!!! His heavy bike doesn't deflect on the rocks, the front wheel is like an immense gyroscope, nothing moves it! In the meantime my bro is laughing at my expensive bike, cause it totally sucks on this trail, and he is 100% correct. So I guess the moral of this story is...........?

    I think that a lot of people enjoyed the discussion errrr ... 'technical garbage' on the effect of frame weight, which was discussed because Itripper swapped bikes with his brother and found the huffy to perform better in the rock garden. Guess you must have missed that part.

  88. #88
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    Quote Originally Posted by gonzostrike
    this thread is ridiculous. what's with all the technical garbage?

    obviously, ltripper's brother is a better or more fearless rider. it's that simple.

    to blame it on the bike is ridiculous in the extreme.

    it doesn't matter that ltripper "has been riding for years" or that his Ibis RidiculoSilk was way more expensive or way more refined.

    Steve Peat could beat me to the bottom of the hill on a Big Wheel, I'm sure. No matter what I was riding.

    ltripper needs to get over the fact that his brother has bigger stones. that's all. it's not at all about the bike, nor about the stupid STUPID STUPID attempts to make this into a technical discussion, when it is NOT about bike design or suspension performance.

    maroons.

    dont want to point out something so obvious while you're dissing people but....

    iltripper specifically stated that he tried the walmart bike and he said it rode much better downhill. his brother also tried his bike and felt like it had poor performance downhill. so the walmart bike was better descending, to both riders. if you had read, im sure you would've seen that. so the issue isn't as simple as saying a rider was better than the other. the walmart bike performed better.

    the question is, WHY? someone proposed that it is because of the WEIGHT of the bike, which is what sprung up all this technical proposals.

    edit: btw. you guys should revive this thread. im wondering about this myself. because i used to ride a diamondback sorrento hard tail. it was built like a tank, heavy as hell. now i ride a <22 lbs stumpjumper comp with a RS sid carbon bars and the works. it climbs like a dream, but it descens noticably worse and is much less stable than my old diamondback with a crappy RST fork. no, im not kidding. im wondering this myself, could it be weight? i would think so, but i dont know for sure. how is it that my stumpjumper is beat up by a $250 dept store bike?

  89. #89

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    I think it comes down to different bikes are made for different types of riding.

    Expensive XC bikes = quick and responsive, light and good climbing

    Expensive DH bikes = crazy ass stunts and soaking up hits, descending like monica on bill

    Cheapo Wal-Mart bikes = meant for recreational, non-hardcore riding
    (My 1st was a wal-mart dual suspension. It was cool, but broke enough to make me get something better)

    Why did the Wal-Mart bike descend better? Because it probably emulated a freeride or downhill bike more than a xc bike. But, match it up to a more expensive, quality bike of similar geometry and then we will see the truth.

  90. #90

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    Quote Originally Posted by summitlt
    All walmart bikes have SUPER soft suspension, all of them. Mostly becaseu they are made for riding of the curbing max. They ride nice, but try and get the bike to fly, its scary.

    Also I used to beat the living piss out of my walmart bike. My new biek I am a little easier on.

    In no way is a walmart better than a good bike. Walmart bieks sucks. Screw them all.
    Gee, I beleive wally world sells schwinns now. Is that where you got yours?

  91. #91
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    Quote Originally Posted by Trail Thumper
    No shyt! I have experienced the same thing. I have a Wally Mongoose that weighs in at about 40 lbs. It can mow thru some stuff my 2500 dollar K2 cant. I just don't get it!

    Bicycling mag listed a Mongoose x-somethin' as a great bike for a beginner at $500 US. Walmart sells that bike up here in Canada for $249, about $200 US. Having enormomonstersuperduperkablang buying power is not nice for our 100 bikes sold/year LBS eh?

  92. #92
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    Quote Originally Posted by scant
    sell me your beautiful ibis for $200 & buy a high end walmat rig & treat yourself with the change? ;D

    ta

    scant
    I'll go a bit higher than that. ;D

    Seriously though, the SilkTi/Ripley/Fango is a bit twitchy with an 80mm fork. Betcha got a racer-long stem, a straight bar and some little semi-slicks on that bike as well. Put it all together and it makes for a nervous Nelly kind of ride when things get bumpy. You won't fit a much larger tire than an ExiWolf 2.1 on the back, but with some bigger meats, a 100mm fork and perhaps a bit of positional tweaking you could maintain nearly all of your uphill advantage while at the same time improving both the geometry and terrain-taming ability of your ride to make it considerably less scary in the rough stuff.

  93. #93

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    uhhh.............have any of u scientists thought of maybe his brothers just better?

  94. #94
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    Walmart a bike shop?

    Let's not forget that a bike assembled at your local bike bistro is going to have a little more assembly time in on it than your typical Walgoose, which is assembled with a hammer and a crescent wrench in the span of roughly ten minutes.

    Then take into account the materials that go into the components, which are Chinese pot metal (they literally melted all their woks when Mao first came into power, as though that would industrialize them) and plastic. The tubing is similar to that stuff under your sink.

    It's a tool box, isn't it? You just take the tools for the job.

  95. #95
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    awesome

    Quote Originally Posted by kenjihara
    Let's not forget that a bike assembled at your local bike bistro is going to have a little more assembly time in on it than your typical Walgoose, which is assembled with a hammer and a crescent wrench in the span of roughly ten minutes.

    Then take into account the materials that go into the components, which are Chinese pot metal (they literally melted all their woks when Mao first came into power, as though that would industrialize them) and plastic. The tubing is similar to that stuff under your sink.

    It's a tool box, isn't it? You just take the tools for the job.


    Dude, you just awoke a 2 year old post. that's awesome.

  96. #96
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    My underwear came from Wal Mart..(yawn). there deli has pretty good chicken, too. Mmmmmm, chicken.

  97. #97
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    Darn, I never read the "date posted" line .....
    Last edited by hardtail05; 03-08-2006 at 03:04 PM.

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