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  1. #1
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    unsprung weight, heavy as possible?

    Hi,

    Just got this opinion from the designer at Pole.

    Anyone experienced want to comment, seems false to me, hence my checking?



    "Personally, I don't see any reasonable point on the coil in forks. The air spring offers a nice ramp up and you can get the spring rate spot on. With coil, you are most likely to have more harsh bottom outs than on air-sprung. There is no fork or shock that will give you the plushest ride ever (similar to moto) because there is no mass on the bike itself that will load the suspension. The SAG is made only by the rider. The only way to make the bike less harsh is to use heavier stuff (tires, wheels, etc.). This is one reason why all Pro's run air springs and DH tires at EWS.
    But... you won't know if you don't try it. I say go for it That's how I learn stuff as well.

    ires (and inserts)are an essential part of the suspension as they damp the ride in the first part of the stroke. The excessive talk about unsprung mass -talk has gone too far and it is actually working counter benefits of the riders. Strong wheels, thick sidewalls, and inserts will make your ride immediately better.
    The "unsprung mass" that you don't feel when you take off the chain and derailleur is actually the lack of movement of the chain and the derailleur that is slapping around. The chain is heavy and the movement of it with the derailleur is causing the feeling of "massive unsprung mass".
    I have ridden light and heavy bikes and the unsprung mass is not the problem. The biggest problem in most cases is too nimble products and a lack of understanding of how suspension works. The bikes that have the most horrible suspension setups have too low tire pressure with light tires, suspension setup way out of the factory standards, light wheels, weird cockpit setup that puts your weight off the ideal, and imbalance of the rear and front springs.



    From my understanding, for the most effective suspension, you want the heaviest frame and lightest wheels going. You want the frame to functionally stay still while the wheel moves over the obstacle.


    Obviously there are other benefits that increase weight, but it's not the increase of weight you want. I run DHR tyres for a ton of benefits, but if they could be magically half the weight it'd be better for suspension?
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?

  2. #2
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    This reminds me of a weird dream I had many years ago. I was riding my mtb and was amazing how smooth the fork felt. I looked down and saw I had a basket mounted in front of the bars and it had a pile of phone books in it. I haven't yet tried this in real life. Are phone books even a thing anymore?

    There are some vids somewhere of guys experimenting with adding weight to their DH bikes. I don't recall the details or outcome.
    Do the math.

  3. #3
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    A lot of dh racers experiment with adding sprung weight to their bikes to change the center of gravity. Reducing unsprung weight reduces the inertia that the suspension needs to overcome in order to react to input. Ask any racecar engineer if they would like less unsprung mass vs sprung mass and you'll get 100% agreement that less unsprung mass is desirable.

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    Air springs are inherently linear in the mid-stroke, combined with methods to overcome initial stiction and most factory damping that is overly-restrictive to prevent fatties from blowing it, it results in having to run very little low-speed compression and lots of blowing through travel, exacerbated by the mid-stroke of the air spring. While they can work acceptably, they will never be linear through most of the travel with a ramp-up at the end. Running too progressive sinks you through the travel and creates deep-stroke harshness, also not a great way to run suspension. I wouldn't pay attention to that person at all.
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  5. #5
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    It does seem like coil forks are mainly used by consumers and not professionals.

    There's no question reducing unsprung mass and increasing sprung mass would help smooth out the ride. However, we're riding bicycles so the amount of mass needed to really see a significant effect would be overall detrimental to performance. It's not like you're going to add a couple pounds to your bike and make it feel like a motocross bike. Which is why DH racers generally worry more about saving weight than adding it, and why their bikes weigh only a few lbs more than enduro bikes.

    Although it does increase unsprung mass, heavier tires and inserts do add a lot of damping. However, I do wonder how many people are after a more plush ride for performance reasons or for comfort. I was having a conversation with someone about Cushcore recently and they were going on about how great the ride quality is improved and they always run Cushcore Pro, even on tamer XC trails. Personally, I don't need a more plush ride on most trails and 260g per wheel is not worth it.

  6. #6
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    That's an interesting point.

    I normally aim for suspension to be smooth, performance tends to follow.

    A quick Google suggests a cruiser has a sprung/unsprung ~17/1
    Motorcross 8/1
    My bike is about 4/1

    Surely the ratio is even more important if its that close?

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    The problem is only in the expectations.
    85-90% of the sprung mass is loaded on the rider's arms and legs, no suspension will ever change that. Expectations that a suspension shoud give a magic carpet ride will only lead to messed up setups.

    Unsprung mass should ideally be as low as possible, but strenght and damping are also necessary... so sometimes you need to give up the noodly rims and bouncy tyres. It's a matter of finding the best compromise here.

    Coils may be more comfortable, if that matters, but modern triple chambe air springs (dual positive, like manitou's) can achieve any curve you may need.

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    The three chamber air spring curve is spot on. I've tuned mine to match the push smashpot.
    However it is not as smooth as my old '03 coil dorado.

    I'm not sure if it due to coil friction or the dynamic change of spring rate when air compresses... Or something else.

    The coil on the back of my bike transmits no detectable spikes or vibration. My old Dorado would feel the same (when weight was far back), new dorado air... Not the same.

    Not sure how we went from a sprung/unsprung chat to coil/air though... Different topics.

    Anyone got any thoughts on the stored energy in a wheel affecting suspension?

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    What’s a push snashpot? Last I checked it’s a Push ACS-3 or a Vorsprung smashpot


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    Interesting points, he's talking about sprung & unsprung mass as different things but then seems to think adding weight has a similar effect regardless which one you add to?

    Sprung vs unsprung weight is the key for sure, increasing sprung weight is almost entirely a positive thing because it makes the suspension work better and reduces vibration transmitted to the rider. Yes the rider is the bulk of the mass but certain vibrations will still be detrimental so reducing them can only be a good thing. Except for the case of very light riders the trade off for increased sprung weight is basically negligible, eg ie adding a kilo or so of weight with coil springs and a dropper post will make the ride far better in one way but the negative influence of weight will be imperceptible.

    Unsprung weight however should be ideally as low as possible but that where you do need to compromise. Strong, wide rims, DH tyres and inserts all have benefits but the extra weight reduces the ability of the wheel to respond to bumps quickly so you do need to carefully pick which ones you need so you aren't adding too much unsprung weight.

    Talk to any car or motorcycle designer and they will all agree that unsprung weight is the one thing that they would always reduce as much as possible given the chance


    Quote Originally Posted by CaveGiant View Post
    Anyone got any thoughts on the stored energy in a wheel affecting suspension?
    Are you talking about the kinetic energy of the wheel in motion or the potetntial energy in the elastic parts eg rim, tyre, spokes?
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    Quote Originally Posted by CaveGiant View Post
    That's an interesting point.

    I normally aim for suspension to be smooth, performance tends to follow.

    A quick Google suggests a cruiser has a sprung/unsprung ~17/1
    Motorcross 8/1
    My bike is about 4/1

    Surely the ratio is even more important if its that close?
    4:1 seems awfully high for a bike. Just doing a rough estimate off the top of my head it seems like an enduro bike would be less than 1.5:1. Did you include your fork lowers and ~1/2 the weight of your rear triangle in the unsprung weight category? Even if I keep it simple and count the entire fork and frame as sprung weight, it still seems like it would be maybe 2:1 at most. Is your bike an e-bike or gearbox bike or something?

  12. #12
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    Quote Originally Posted by CaveGiant View Post
    The three chamber air spring curve is spot on. I've tuned mine to match the push smashpot.
    However it is not as smooth as my old '03 coil dorado.

    I'm not sure if it due to coil friction or the dynamic change of spring rate when air compresses... Or something else.

    The coil on the back of my bike transmits no detectable spikes or vibration. My old Dorado would feel the same (when weight was far back), new dorado air... Not the same.

    Not sure how we went from a sprung/unsprung chat to coil/air though... Different topics.

    Anyone got any thoughts on the stored energy in a wheel affecting suspension?
    A big problem in air springs is stiction. Not always a huge problem on some trails/situations, as I kind of prefer it on real smooth "flow" trails, it provides a lot of LSC and firm feel, but that resistance to movement adds to a lot of harshness in chunky situations where the shock has to change direction quickly.

    Maybe a pertinent story: For an enduro race this summer, I went with my rear air-shock setup, with the reasoning above of "faster", due to firmer and better pedaling performance and ability to "pump" on terrain. I crashed on a rooty off-camber section where my rear coil would "stick" just fine. On the air shock, it just didn't have the traction and I couldn't manage the line. My take-away was to not change anything from the setup that "works" for non-race conditions...just try/go faster.

    You have a tradeoff. You can have a simple air shock with minimal stiction that has a more "classic" air spring curve, or you can have a more complicated one that gets a more coil like or optimal curve, but with significantly increased stiction due to the more complex seal arrangement necessary. IME, proper damping can really fill a lot of the middle ground, it can avoid some of the deep-stroke harshness and also allow the LSC to be more effective without feeling like a jackhammer, but this usually takes aftermarket/custom tuning to achieve. This is a big reason why people switch to the Push or similar coil spring conversions for their Pike/Lyrik forks and such, because the stock damping will work decently enough if paired with a decent spring. Conversely, you could take the stock spring and modify the damping to work much better. Which is the "best" gets to be subjective.

    Air springs are great because you can tune them. I'd much rather show up at a bike park and rent a bike with air shocks on both ends, rather than end up with something that is hundreds of lbs under or over sprung for my weight. But OEM damping generally sucks, so again, it depends on which way you want to go. Modify the spring, or modify the damper. Both have advantages and disadvantages.

    This topic was in the OP and I think it generally speaks to the (lack of) credibility of the person referenced. He's known for really off-the-wall stuff that has no basis in reality.
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    Quote Originally Posted by Jayem View Post
    This topic was in the OP and I think it generally speaks to the (lack of) credibility of the person referenced. He's known for really off-the-wall stuff that has no basis in reality.
    I don’t know; geometry numbers have been slowly trending closer and closer to the numbers his bikes have had for years now. A few bikes that came out this past year (Specialized Enduro, Norco Sight, Banshee Titan, etc.) are starting to get pretty damn close too. Off the wall? Sure, at times. But I think the guy deserves some recognition at this point.

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    Good spot, you can guess I was half asleep when I wrote this.
    Push acs-3 is what I meant.

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    Quote Originally Posted by dlxah View Post
    4:1 seems awfully high for a bike. Just doing a rough estimate off the top of my head it seems like an enduro bike would be less than 1.5:1. Did you include your fork lowers and ~1/2 the weight of your rear triangle in the unsprung weight category? Even if I keep it simple and count the entire fork and frame as sprung weight, it still seems like it would be maybe 2:1 at most. Is your bike an e-bike or gearbox bike or something?
    Included everything (with a bit of estimation).
    Total weight was 18.8kg
    Front wheel 3
    Kilo for dorado lowers

    Rear wheel + bouncy bits probably 5kg.

    So about 1:1, erm I was way off =l

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    Quote Originally Posted by dlxah View Post
    I don’t know; geometry numbers have been slowly trending closer and closer to the numbers his bikes have had for years now. A few bikes that came out this past year (Specialized Enduro, Norco Sight, Banshee Titan, etc.) are starting to get pretty damn close too. Off the wall? Sure, at times. But I think the guy deserves some recognition at this point.
    I'm a fan of some of his ideas, not so much on others.

    There were certain things I wanted on a bike, certain things I was unsure on.

    It's hard to deny the geometry of the rear end is Imo near perfect.

    However the fact the frame stack stays the same for all sizes, as does the triangle, makes the bike very weird in the outlying sizes.
    The suspension was the other major issue. Stock shock/tune was awful.

    The main thing I do not understand is that why the design suffers from hang up so badly. Unless the suspension is really finely tuned every single root/bump saps speed.

    I've had to get one of the best best forks made custom shimmed, at significant expense, to make it work with this bike.

    Why is it so damn picky on setup!

    Stick me on any bike and I'm normally fine.

    I've had some good rides on wifey's bike without adjusting anything (she is a foot shorter and half my weight). I've taken a road bike on a DH course (OK that one was hard... But fun).

    So why is this bike so difficult!

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    Quote Originally Posted by jeremy3220 View Post
    It does seem like coil forks are mainly used by consumers and not professionals.
    This has no bearing on what's right, wrong, good, or bad.

    People need to stop thinking they should set up their bikes like "professionals", or that it's some kind of great benchmark. Paid athletes (racers) riding what they're told to ride, and the bikes are setup for doing a very specific job.
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    Stop asking how much it weighs and just go ride it.

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    Quote Originally Posted by *OneSpeed* View Post
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    This has no bearing on what's right, wrong, good, or bad.

    People need to stop thinking they should set up their bikes like "professionals", or that it's some kind of great benchmark. Paid athletes (racers) riding what they're told to ride, and the bikes are setup for doing a very specific job.
    It does have a bearing on performance applications. Obviously Im not claiming that whatever suits the pros is going to be ideal for OP.

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    Quote Originally Posted by jeremy3220 View Post
    It does have a bearing on performance applications.
    No, it doesn't. Example: define "performance". If the goal is FUN then the suspension is performing better, there's no stopwatch involved, and the results are subjective.

    The only professional racer that should be referenced is an independent person with no sponsors and an unlimited budget. They would be the only ones with access to anything and not limited to the products they're sponsored by.

    If a pro rider is not sponsored by Push, even if it's the best performing fork/shock on the market, a pro racer will not be running it. They'll be stuck with whatever their sponsor makes. Now apply that logic to every component on the bike.
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    Quote Originally Posted by *OneSpeed* View Post
    No, it doesn't. Example: define "performance". If the goal is FUN then the suspension is performing better, there's no stopwatch involved, and the results are subjective.
    I'm talking about riders who are pros at having fun of course.

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    Quote Originally Posted by CaveGiant View Post
    From my understanding, for the most effective suspension, you want the heaviest frame and lightest wheels going. You want the frame to functionally stay still while the wheel moves over the obstacle.
    I accomplished this once (by accident) while running my suspension at 40% sag. It was interesting, but the ground kept getting in the way of my pedals...
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    Quote Originally Posted by CaveGiant View Post
    I'm a fan of some of his ideas, not so much on others.

    There were certain things I wanted on a bike, certain things I was unsure on.

    It's hard to deny the geometry of the rear end is Imo near perfect.

    However the fact the frame stack stays the same for all sizes, as does the triangle, makes the bike very weird in the outlying sizes.
    The suspension was the other major issue. Stock shock/tune was awful.

    The main thing I do not understand is that why the design suffers from hang up so badly. Unless the suspension is really finely tuned every single root/bump saps speed.

    I've had to get one of the best best forks made custom shimmed, at significant expense, to make it work with this bike.

    Why is it so damn picky on setup!

    Stick me on any bike and I'm normally fine.

    I've had some good rides on wifey's bike without adjusting anything (she is a foot shorter and half my weight). I've taken a road bike on a DH course (OK that one was hard... But fun).

    So why is this bike so difficult!
    My guess would be weird rear axle path with rear wheel hanging up on stuff instead of getting over them .

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    What model is yours again? The frames of his ive worked on were incredibly progressive which takes careful tuning for sure

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    Quote Originally Posted by CaveGiant View Post
    Anyone experienced want to comment
    There's a lot to unpack here.

    1) Coils more likely to have harsh bottom-outs - probably not. Maybe a poorly-designed one. Both the Vorsprung Smashpot and PUSH ACS-3 have anti-bottom systems (supplementary air spring or hydraulic damper) that work. And there's many options for coil spring rear shocks. You're only likely to have an issue if your shock can't be set up for your bike, such as an unsuitable leverage ratio.

    2) Pros don't run coils - no. It seems to be a mix in the EWS (Pinkbike, VitalMTB). I haven't done a survey. The video of Curtis Keene testing a coil shock a couple years ago is what got me to try a coil on my Nomad (v3) and I still ride coil on my Nomad (v4). My other bike (5010 v2) is still on air.

    3) You won't know if you don't try - go for it - YES. What works for someone else may not work for you. This includes the pros, by the way. Jordi Cortes comments in one of the Fox Dialed videos (I can't find which one specifically but it was from this season) about how even a pro "only" going at 90% of race pace isn't going to be happy with a setup for full race pace.

    4) Tires (and inserts) are essential - YES. I can feel a difference just from knob thickness between a fresh set of tires and my old set (same make/model/pressure), let alone changing make/model/pressure or casing or inserts.

    5) Chain/deraileur example - meh? I'm not sure what to make of this. I just think of Gwin's chainless run and how well his suspension responded without it... but to me that was more about direct interaction between the suspension and the drivetrain through the tension in the chain between the rear cog and front ring.

    6) Setup matters - YES. Nothing more to say about this.

    7) More unsprung mass is better - No. I'm not sure any of the posters here think it's true. We want our wheels to track the ground (item 4 on the list from Vorsprung when thinking about "correct setup"). I'm also not sure the original comments in the original post address unsprung mass in a meaningful way. It seems to ramble around many of the previous points instead.

    ¯\_(ツ)_/¯

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    Quote Originally Posted by JohnnyC7 View Post
    What model is yours again? The frames of his ive worked on were incredibly progressive which takes careful tuning for sure
    Evolink 158 Xl.

    Any applicable advice?

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    Quote Originally Posted by tbmaddux View Post
    There's a lot to unpack here.

    1) Coils more likely to have harsh bottom-outs - probably not. Maybe a poorly-designed one. Both the Vorsprung Smashpot and PUSH ACS-3 have anti-bottom systems (supplementary air spring or hydraulic damper) that work. And there's many options for coil spring rear shocks. You're only likely to have an issue if your shock can't be set up for your bike, such as an unsuitable leverage ratio.

    2) Pros don't run coils - no. It seems to be a mix in the EWS (Pinkbike, VitalMTB). I haven't done a survey. The video of Curtis Keene testing a coil shock a couple years ago is what got me to try a coil on my Nomad (v3) and I still ride coil on my Nomad (v4). My other bike (5010 v2) is still on air.

    3) You won't know if you don't try - go for it - YES. What works for someone else may not work for you. This includes the pros, by the way. Jordi Cortes comments in one of the Fox Dialed videos (I can't find which one specifically but it was from this season) about how even a pro "only" going at 90% of race pace isn't going to be happy with a setup for full race pace.

    4) Tires (and inserts) are essential - YES. I can feel a difference just from knob thickness between a fresh set of tires and my old set (same make/model/pressure), let alone changing make/model/pressure or casing or inserts.

    5) Chain/deraileur example - meh? I'm not sure what to make of this. I just think of Gwin's chainless run and how well his suspension responded without it... but to me that was more about direct interaction between the suspension and the drivetrain through the tension in the chain between the rear cog and front ring.

    6) Setup matters - YES. Nothing more to say about this.

    7) More unsprung mass is better - No. I'm not sure any of the posters here think it's true. We want our wheels to track the ground (item 4 on the list from Vorsprung when thinking about "correct setup"). I'm also not sure the original comments in the original post address unsprung mass in a meaningful way. It seems to ramble around many of the previous points instead.

    ¯\_(ツ)_/¯
    My interpretation of Leo's quote in the OP is that point number 4 here is more important than point number 7. I don't think he was actually advocating increasing unsprung mass just for the sake of increasing unsprung mass but rather not compromising tire, rim, and insert selections in an effort to minimize unsprung mass. I'm with you on points 1 and 2, though.

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    Quote Originally Posted by jeremy3220 View Post
    It does have a bearing on performance applications. Obviously Im not claiming that whatever suits the pros is going to be ideal for OP.
    A freshly servised air spring works great for a race and saves weight. But stiction will increase quickly. I switched to coil since weekly spring lubing sucks as much as the performance degrading.

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    Quote Originally Posted by tbmaddux View Post

    7) More unsprung mass is better - No.

    ¯\_(ツ)_/¯
    I agree, especially in auto racing.

    My only thought about why someone would say "more unsprung weight is better" is perhaps that it helps the bike feel more stable/planted? Which is obviously subjective and/or personal preference.

    I don't agree, if this is what he's saying, that higher unsprung weight makes the suspension work better.
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    Quote Originally Posted by Cerberus75 View Post
    A freshly servised air spring works great for a race and saves weight. But stiction will increase quickly. I switched to coil since weekly spring lubing sucks as much as the performance degrading.
    You switched to coil forks?

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    Why do you want less UNSPRUNG weight?
    - It takes less energy to move it. Properties of mass with inertia. More mass=more inertia=more energy needed to initiate movement. In the suspension world, if you need to have more energy to move your unsprung weight, the suspension spring is not absorbing the impact. Instead, the energy is being transfered into the material, and then through to you the rider.

    Why is having LESS SPRUNG weight a good thing?

    - Suspension is ususally rated in kg/mm. Meaning, for every millimeter of travel, it takes XX amount of KG of force to move. When you have more weight holding the suspension down, you "preload it" with your sag. So, if the suspension is sagging 10mm, and you have a spring (air or coil, it doesn't matter) of 5.0kg/mm, you have 50kg of force pushing down on the suspension at that moment, even just sitting there. Now, it only takes another 5kg of force to move the suspension 1mm, but, the total amout of energy stored in the suspension is still greater. In the case of air suspension, that kg/mm number will ALWAYS be a constantly increasing number. (Since air is ALWAYS progressive) As that number goes up, the suspension spring will become stiffer.

    When you have a lot of mass to the sprung weight, you are increasing the inertia of that object, so it is much less affected by the energy being imparted on the suspension, but thats about it. You still have all of the drawbacks of more mass. (greater suspension stiffness being needed, less maneuverability, and such and so forth.)
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    Quote Originally Posted by DethWshBkr View Post
    In the case of air suspension, that kg/mm number will ALWAYS be a constantly increasing number. (Since air is ALWAYS progressive) As that number goes up, the suspension spring will become stiffer.
    Erm....depending on the size of the negative chamber an air spring typically DECREASES in rate for the first ~25%, is linear for a short while and then becomes progressive

    Re: sprung mass, it takes a pretty huge increase to become a hinderance. You may feel (or think you feel) a difference but it probably isn't measurably worse. The increased stability and reduced harshness tends to outweigh any perceived disadvantages

    ie you can literally just add weight to a frame in strategic places and it will improve how the bike rides all on it's own

    You would never see it admitted publicly but it is not uncommon for race teams to add weight inside the frames if a bike is too light

    I encourage people to go get some 1 pound weights and experiment with attaching them to the frame, then attaching them to the swingarm or forkleg to see how it feels
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    Quote Originally Posted by JohnnyC7 View Post
    Erm....depending on the size of the negative chamber an air spring typically DECREASES in rate for the first ~25%, is linear for a short while and then becomes progressive

    Re: sprung mass, it takes a pretty huge increase to become a hinderance. You may feel (or think you feel) a difference but it probably isn't measurably worse. The increased stability and reduced harshness tends to outweigh any perceived disadvantages

    ie you can literally just add weight to a frame in strategic places and it will improve how the bike rides all on it's own

    You would never see it admitted publicly but it is not uncommon for race teams to add weight inside the frames if a bike is too light

    I encourage people to go get some 1 pound weights and experiment with attaching them to the frame, then attaching them to the swingarm or forkleg to see how it feels
    You even have road bike manufacturers that intentionally come in under weight so that the riders can strategically place weights to tune how they want the bike to handle.

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    Quote Originally Posted by jeremy3220 View Post
    You switched to coil forks?
    Yeah, got a push kit with an Avalanche cartridge. Mid stroke and traction is better. No stiction.

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    Quote Originally Posted by JohnnyC7 View Post
    Erm....depending on the size of the negative chamber an air spring typically DECREASES in rate for the first ~25%, is linear for a short while and then becomes progressive
    Perhaps by using secondary chambers, fancy valving and such, you can simulate a digressive or linear rate, but an air chamber itself is always progressive.

    If you have a secondary chamber open up shortly after motion starts, you get the additional volume, which reduces the rate at which the spring ramps.

    Where is there an air spring that the spring itself has a linear or digressive rate? I'd like to see that.

    Race teams DO have to add wieght quite often. It's not to help the suspension, but to get the weight as LOW AS POSSIBLE, to aid in handling.


    Why do MX teams spend ridiculous amounts of money to get a bike from 235 lb to 230 lb? Handling. Why do they contstantly struggle to get the wheels and the forks, brakes, and tires as light as possible if unsprung weight didn't matter? Why do local racers spend thousands of dollars on titanium exhaust systems, titanium valves, and ultra light parts? Mass, momentum, and inertia. It does make a difference. And yes, a pound of weight on a bicycle is a HUGE change. People spend many thousands of dollars to reduce the MX bike weights, where 1 lb is a measly .5% total weight.

    Why did Trek for example, made a road bike that weighs OVER A POUND under the UCI legal limit? They had to add weight. They added ballast weight to the bottom bracket. Handling. Getting the weight LOW is nearly always better for handling. Something scale weight alone cannot quantify.
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    Quote Originally Posted by DethWshBkr View Post
    Perhaps by using secondary chambers, fancy valving and such, you can simulate a digressive or linear rate, but an air chamber itself is always progressive.
    No, I think JohnnyC7 is right. Most modern air shocks use a negative air chamber to minimize preload. The negative air chamber causes these shocks to have a regressive rate at the beginning of the stroke. Larger negative chamgers reduce the effect, but it's still there. You can see the regressive rate in the bottom left corner of this graph from Fox's website before the rate starts to progress again about 1/3 of the way into the stroke:



    The exception to this would be air springs that use a coil negative spring instead of a negative air chamber such as DVO's OTT forks.
    Attached Thumbnails Attached Thumbnails unsprung weight, heavy as possible?-float-air-spring-curves.jpg  

    Last edited by dlxah; 01-03-2020 at 12:04 AM. Reason: Hopefully fixed the image

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    Quote Originally Posted by DethWshBkr View Post
    Perhaps by using secondary chambers, fancy valving and such, you can simulate a digressive or linear rate, but an air chamber itself is always progressive.

    If you have a secondary chamber open up shortly after motion starts, you get the additional volume, which reduces the rate at which the spring ramps.

    Where is there an air spring that the spring itself has a linear or digressive rate? I'd like to see that.
    Agreed, I'm thinking he was confusing leverage curves with springs?

    Here's a good reference for anyone that wants to learn/nerd out on leverage curves, and common suspension designs. Scroll to the "leverage curves vs spring curves" most of the way down for a specific description of what we're talking about. Towards the end they get into the details about curves and such.

    https://www.bikeradar.com/features/t...nsion-systems/

    Race teams DO have to add wieght quite often. It's not to help the suspension, but to get the weight as LOW AS POSSIBLE, to aid in handling.


    Why do MX teams spend ridiculous amounts of money to get a bike from 235 lb to 230 lb? Handling. Why do they contstantly struggle to get the wheels and the forks, brakes, and tires as light as possible if unsprung weight didn't matter? Why do local racers spend thousands of dollars on titanium exhaust systems, titanium valves, and ultra light parts? Mass, momentum, and inertia. It does make a difference. And yes, a pound of weight on a bicycle is a HUGE change. People spend many thousands of dollars to reduce the MX bike weights, where 1 lb is a measly .5% total weight.

    Why did Trek for example, made a road bike that weighs OVER A POUND under the UCI legal limit? They had to add weight. They added ballast weight to the bottom bracket. Handling. Getting the weight LOW is nearly always better for handling. Something scale weight alone cannot quantify.
    The weight savings you describe as hugely beneficial is only applicable to the pointy end of the racing spectrum. Anyone not racing at an extremely high level has far less to gain by spending thousands of dollars. Especially when motors aren't involved. And especially for anyone who doesn't race.

    I'm not disagreeing with you, just pointing out that an average weekend warrior will not benefit much from saving 1lb on a trail/enduro bike. Depending where the weight is saved, it might go completely unnoticed, and will not change the results of a casual racer. (It's 80% the rider, 20% the bike.)
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  37. #37
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    Quote Originally Posted by dlxah View Post
    No, I think JohnnyC7 is right. Most modern air shocks use a negative air chamber to minimize preload. The negative air chamber causes these shocks to have a regressive rate at the beginning of the stroke. Larger negative chamgers reduce the effect, but it's still there. You can see the regressive rate in the bottom left corner of this graph from Fox's website before the rate starts to progress again about 1/3 of the way into the stroke:



    The exception to this would be air springs that use a coil negative spring instead of a negative air chamber such as DVO's OTT forks.
    The neg chamber is not intended to do anything for preload.
    The negative air spring is intended to reduce the amount of force required to initiate motion. Since all springs have a certain "force per millimeter of motion", it requires that certain amount of force to get moving. By having a negative spring, you are reducing the amount of force needed to initiate motion on the main spring, because you have a secondary spring (negative) pressing against your mainspring. So if it takes 5 kg to move it a millimeter, if I add a 4 kg negative spring, the first millimeter of travel will only take 1 kg. Then the negative spring begins to lose effectiveness. The next millimeter of travel might only have 3.95 kg of negative spring force, so instead of 1kg external being needed, you need 1.05.

    That is still a progressive spring rate for the mainspring, regardless of what the negative spring is doing.
    Unfortunately your picture did not show up for me.

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    Quote Originally Posted by *OneSpeed* View Post

    .... an average weekend warrior will not benefit much from saving 1lb on a trail/enduro bike. Depending where the weight is saved, it might go completely unnoticed, and will not change the results of a casual racer.

    In a strictly data point way, no, but practically, ABSOLUTELY true.

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    Quote Originally Posted by DethWshBkr View Post
    Since all springs have a certain "force per millimeter of motion", it requires that certain amount of force to get moving.

    Bro that's preload

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    Quote Originally Posted by PhillipJ View Post
    Bro that's preload
    No, that's spring rate.

    Preload is how much energy is stored in the spring by compressing it.
    Same numbers - 5kg/mm, if I have a sag of 10mm, the spring is "preloaded" with 50kg of force.

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    Quote Originally Posted by DethWshBkr View Post

    Preload is how much energy is stored in the spring

    Yeah. And how much energy is in an uncompressed air spring?

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    Quote Originally Posted by DethWshBkr View Post
    Unfortunately your picture did not show up for me.
    Sorry about that. I think I fixed it?

    Quote Originally Posted by DethWshBkr View Post
    Preload is how much energy is stored in the spring by compressing it.
    Same numbers - 5kg/mm, if I have a sag of 10mm, the spring is "preloaded" with 50kg of force.
    We are getting completely off topic here, but what you're describing here is the spring rate not the preload. In your example we would say the spring is "loaded" with 50 kg of mass not "preloaded".

    https://youtu.be/iTdfxpBurmg?t=63

    If you'd like to discuss this further, then I suggest we start a separate thread.

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    Quote Originally Posted by dlxah View Post
    Sorry about that. I think I fixed it?



    We are getting completely off topic here, but what you're describing here is the spring rate not the preload. In your example we would say the spring is "loaded" with 50 kg of mass not "preloaded".

    https://youtu.be/iTdfxpBurmg?t=63

    If you'd like to discuss this further, then I suggest we start a separate thread.
    It's good here =)

    There is also the nice part about if you compress air quickly it will have a higher spring rate than if compressed slowly.
    Potentially useful for large drops, quite the opposite on sharp spikes.

    I've not done the maths yet, so not sure how large the effect is!

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    Quote Originally Posted by DethWshBkr View Post
    ...Since all springs have a certain "force per millimeter of motion", it requires that certain amount of force to get moving.
    Quote Originally Posted by PhillipJ View Post
    Bro that's preload
    Quote Originally Posted by DethWshBkr View Post
    No, that's spring rate.

    Preload is how much energy is stored in the spring by compressing it.
    Same numbers - 5kg/mm, if I have a sag of 10mm, the spring is "preloaded" with 50kg of force.
    Quote Originally Posted by PhillipJ View Post
    Yeah. And how much energy is in an uncompressed air spring?
    @DethWshBkr is correct, that's spring rate.

    Spring rate is the amount of weight required to compress a spring a given distance.

    Preload is and amount of compression put on a spring to adjust the sag and shouldn't affect the spring rate (if you use a spring with too low a spring rate and add preload to get the right sag the spring will still be too soft). https://accutuneoffroad.com/articles...eload-matters/

    Note that (assuming no change in preload) an increase in spring rate in a coil spring will decrease sag, just like on an air spring.

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    Quote Originally Posted by Surestick Malone View Post
    Spring rate is the amount of weight required to compress a spring a given distance.

    Preload is and amount of compression put on a spring to adjust the sag and shouldn't affect the spring rate (if you use a spring with too low a spring rate and add preload to get the right sag the spring will still be too soft). https://accutuneoffroad.com/articles...eload-matters/

    Note that (assuming no change in preload) an increase in spring rate in a coil spring will decrease sag, just like on an air spring.
    This is more or less correct, but go back and re-read what DethWshBkr posted. He seems to be confusing spring rate and preload as if they're the same thing or something.

    Quote Originally Posted by DethWshBkr View Post
    Since all springs have a certain "force per millimeter of motion"
    That is spring rate.

    Quote Originally Posted by DethWshBkr View Post
    it requires that certain amount of force to get moving. By having a negative spring, you are reducing the amount of force needed to initiate motion on the main spring, because you have a secondary spring (negative) pressing against your mainspring.
    That is preload.

    Quote Originally Posted by DethWshBkr View Post
    So if it takes 5 kg to move it a millimeter, if I add a 4 kg negative spring, the first millimeter of travel will only take 1 kg. Then the negative spring begins to lose effectiveness. The next millimeter of travel might only have 3.95 kg of negative spring force, so instead of 1kg external being needed, you need 1.05.
    Now he's talking about spring rate.

    Quote Originally Posted by DethWshBkr View Post
    Preload is how much energy is stored in the spring by compressing it.
    Same numbers - 5kg/mm, if I have a sag of 10mm, the spring is "preloaded" with 50kg of force.
    And that sounds like spring rate again.

    Preload is how much energy is stored in a spring at top out. It can also be thought of as how much force is required to start compressing the spring. The spring rate is how much force it takes to compress the spring a certain amount (usually an inch) excluding any preload. It can also be thought of as how much energy is stored in a spring for a certain amount of compression. If a spring has a linear spring rate of 100 lbs/in and 10 lbs of preload, then it won't compress at all until you apply more than 10 lbs or force. It will take a load of 110 lbs to compress it the first inch and 100 more lbs for each additional inch until bottom out (e.g. 210 lb load to compress it 2 inches, 310 lb for 3 inches, etc.).

    If the spring rate is 5 kg/mm (strange units, but okay I guess), and you have 10mm of sag with a 50kg load, then the spring must have zero preload on it. 5 kg/mm * 10mm = 50 kg. I suppose he could mean that there is 10mm of preload wound onto the coil, but I'm going to assume that's not the case. "Sag" implies the spring has a load on it, and in the context of mountain biking, 10mm/50kg would be a ridiculous amount of preload. If you have that much preload on a bike shock, you clearly need a firmer spring rate.

    This article does a good job of explaining it with a few graphs:
    https://www.cycleworld.com/sport-rid...e-and-preload/
    Last edited by dlxah; 01-04-2020 at 01:11 AM.

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    The entire context of this preload/spring rate conversation is the use of negative springs.
    Negative springs are important for air sprung suspension because there is significant energy stored at top out. That is equivalent to winding on a lot of preload on a coil spring even though you're not compressing the air spring. The force generated by the negative spring can balance this preload so you don't need such a large increase in force to initiate movement. Actual spring rate is irrelevant.

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    Quote Originally Posted by Surestick Malone View Post
    @DethWshBkr is correct, that's spring rate.

    Spring rate is the amount of weight required to compress a spring a given distance.

    Preload is and amount of compression put on a spring to adjust the sag

    The energy stored in an airspring at topout is equivalent to preload on a coil.

    DethWshBkr is only partially correct and also quite confused.

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    So much spring confusion above, seems to be more an argument on terminology than engineering though. If I get involved I'd probably make it worse not better


    This might be interesting for some.
    You can make a spring very linear as long as you have a 3 chamber and large neg.

    Typically I can't upload photos from my phone!
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?

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    Name:  1297011d1575141037t-3-chamber-air-spring-calculator-ok-does-2-well-screenshot_20191130-190008_ex.jpg
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    Nicely tuned dorado (compared to a coil)
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?

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    Rockshox air springunsprung weight, heavy as possible?-1297013d1575709065-3-chamber-air-spring-calculator-ok-does-2-well-screenshot_20191130-190424_exc.jpg
    Why would I care about 150g of bike weight, I just ate 400g of cookies while reading this?

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    Quote Originally Posted by CaveGiant View Post
    Hi,

    Just got this opinion from the designer at Pole.

    Anyone experienced want to comment, seems false to me, hence my checking?



    "Personally, I don't see any reasonable point on the coil in forks. The air spring offers a nice ramp up and you can get the spring rate spot on. With coil, you are most likely to have more harsh bottom outs than on air-sprung. There is no fork or shock that will give you the plushest ride ever (similar to moto) because there is no mass on the bike itself that will load the suspension. The SAG is made only by the rider. The only way to make the bike less harsh is to use heavier stuff (tires, wheels, etc.). This is one reason why all Pro's run air springs and DH tires at EWS.
    But... you won't know if you don't try it. I say go for it That's how I learn stuff as well.

    ires (and inserts)are an essential part of the suspension as they damp the ride in the first part of the stroke. The excessive talk about unsprung mass -talk has gone too far and it is actually working counter benefits of the riders. Strong wheels, thick sidewalls, and inserts will make your ride immediately better.
    The "unsprung mass" that you don't feel when you take off the chain and derailleur is actually the lack of movement of the chain and the derailleur that is slapping around. The chain is heavy and the movement of it with the derailleur is causing the feeling of "massive unsprung mass".
    I have ridden light and heavy bikes and the unsprung mass is not the problem. The biggest problem in most cases is too nimble products and a lack of understanding of how suspension works. The bikes that have the most horrible suspension setups have too low tire pressure with light tires, suspension setup way out of the factory standards, light wheels, weird cockpit setup that puts your weight off the ideal, and imbalance of the rear and front springs.



    From my understanding, for the most effective suspension, you want the heaviest frame and lightest wheels going. You want the frame to functionally stay still while the wheel moves over the obstacle.


    Obviously there are other benefits that increase weight, but it's not the increase of weight you want. I run DHR tyres for a ton of benefits, but if they could be magically half the weight it'd be better for suspension?
    Yeah that's weird.

    Your bike suspension has two frequencies:
    The slow frequency is the rider and bike chassis bouncing up and down on the suspension.
    The fast frequency is the wheels and unsprung mass moving up and down against the ground.

    The bigger the difference in the two masses (sprung vs unsprung) the bigger the difference in these frequencies and the better your suspension can handle fast rough ground.

    But. On bikes our sprung mass isn't uniform like a car is. It's a light bike and then another set of four springs and dampers (arms and legs) connecting the rest of the sprung mass.

    This is the bit that throws up massive differences between our suspension tunes and cars and motorbikes. It's why a lot of suspension tuners using car or motorbike theory produce some absolutely awful results.

    The only performance downside to coil springs is weight and getting the correct weight. Harsh bottom-out isn't an issue. We have correctly tuned dampers and bumpers for that. Not to mention hydraulic bottom-out.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
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    I'll throw a hand grenade in the room.

    I ride ebikes too nowdays, I get to try a lot of others bikes and even my own bike (merida e160) has the best suspension on any bike I've ever ridden shy of my Devinci wilson. In fact basically any ebike I've ridden has had superior suspspension manners than any enduro bike I've owned. It's fascinating and frustrating at the same time. These bikes are no joke on the downhills.

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    Quote Originally Posted by CaveGiant View Post
    Evolink 158 Xl.

    Any applicable advice?
    Ok they don't appear to have anywhere near as much progression overall as the stamina, but the force does increase at a higher rate early in the travel, then tapers off towards the end to allow it to reach the end of the stroke easier. Just looking at it though the first half of the stroke will feel pretty firm so probably a good candidate for a progressive coil
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  54. #54
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    Quote Originally Posted by brash View Post
    I'll throw a hand grenade in the room.

    I ride ebikes too nowdays, I get to try a lot of others bikes and even my own bike (merida e160) has the best suspension on any bike I've ever ridden shy of my Devinci wilson. In fact basically any ebike I've ridden has had superior suspspension manners than any enduro bike I've owned. It's fascinating and frustrating at the same time. These bikes are no joke on the downhills.
    The one with X2 on the back and FIT4 in the fork?

    Can I ask what other suspension you've ridden?
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    Quote Originally Posted by Dougal View Post
    The one with X2 on the back and FIT4 in the fork?

    Can I ask what other suspension you've ridden?
    2019, X2 up back and Grip2 36 "e-bike" (34 air piston) up front

    Other bikes, stumpy evo, 36 Rhythym with smashpot & Super Deluxe with megneg and tractive tune

    DH bike is Sworks Demo, Fox 40 RC2 with vorsprung valving, Ohlins TTX rear tuned by NS Dynamics.

    I got a OK idea of what works and what doesn't

    I'll do as far as saying the Ebike has more grip that the DH bike in off camber, it's ridiculous!

  56. #56
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    Quote Originally Posted by brash View Post
    2019, X2 up back and Grip2 36 "e-bike" (34 air piston) up front

    Other bikes, stumpy evo, 36 Rhythym with smashpot & Super Deluxe with megneg and tractive tune

    DH bike is Sworks Demo, Fox 40 RC2 with vorsprung valving, Ohlins TTX rear tuned by NS Dynamics.

    I got a OK idea of what works and what doesn't

    I'll do as far as saying the Ebike has more grip that the DH bike in off camber, it's ridiculous!
    Sounds like you need to strap some ballast to your acoustic bikes for a few runs.
    Owner of www.shockcraft.co.nz, Mech Engineer, Tuner, Manitou, Motorex, Vorsprung EPTC, SKF, Enduro
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  57. #57
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    Quote Originally Posted by Dougal View Post
    Your bike suspension has two frequencies:
    The slow frequency is the rider and bike chassis bouncing up and down on the suspension.
    The fast frequency is the wheels and unsprung mass moving up and down against the ground.

    The bigger the difference in the two masses (sprung vs unsprung) the bigger the difference in these frequencies and the better your suspension can handle fast rough ground.

    But. On bikes our sprung mass isn't uniform like a car is. It's a light bike and then another set of four springs and dampers (arms and legs) connecting the rest of the sprung mass.

    This is the bit that throws up massive differences between our suspension tunes and cars and motorbikes. It's why a lot of suspension tuners using car or motorbike theory produce some absolutely awful results.

    The only performance downside to coil springs is weight and getting the correct weight. Harsh bottom-out isn't an issue. We have correctly tuned dampers and bumpers for that. Not to mention hydraulic bottom-out.
    Couldn't agree more!

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    Quote Originally Posted by Dougal View Post
    Sounds like you need to strap some ballast to your acoustic bikes for a few runs.
    That's one of the reasons I went with a heavy frame. The levo suspension was amazing, the enduro was awful. Suspended/unsuspended ratio is important!

    As is a good damper, Douglal's design makes the bike obscenely faster!

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    Quote Originally Posted by CaveGiant View Post
    That's one of the reasons I went with a heavy frame. The levo suspension was amazing, the enduro was awful. Suspended/unsuspended ratio is important!

    As is a good damper, Douglal's design makes the bike obscenely faster!
    Having the damper rates correct for the amount of chassis vs rider weight is very important. As is rider strength.

    Which brings me to the next point. If you want your fork to work better and harder, start doing push-ups.
    Rider strength (and rider fatigue) is a huge driver in making the suspension work. This is why everyone thinks their forks are working great at the start of a long ride and feeling terrible at the end.

    As your arm strength wanes the fork effectively has less force to work against and starts feeling oversprung and overdamped.
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    Quote Originally Posted by Dougal View Post
    Your bike suspension has two frequencies:
    The slow frequency is the rider and bike chassis bouncing up and down on the suspension.
    The fast frequency is the wheels and unsprung mass moving up and down against the ground.

    The bigger the difference in the two masses (sprung vs unsprung) the bigger the difference in these frequencies and the better your suspension can handle fast rough ground..
    Wouldn't the latter frequency be inversely proportional to wheel diameter? Weight differences aside, does this mean that bigger wheels actually result in worse suspension performance on fast rough ground? Obviously if that's the case, the benefit of increased rollover from the big wheels must outweigh that effect, since I think we can all agree that bigger wheels feel smoother over chunky terrain despite being heavier too. I just thought it was interesting.

  61. #61
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    Yes the increased weight of 29" wheels is a negative, but the larger radius makes the acceleration and peak speed (or frequency) of the wheel travelling over the bump lower so the effects kinda cancel out to a degree.

    Another thing to consider is a wheel travelling at a higher speed has more energy than a wheel that weighs more by the same percentage. Therefore reducing the speed of the wheel will make it track the ground better than reducing the weight
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  62. #62
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    Quote Originally Posted by dlxah View Post
    Wouldn't the latter frequency be inversely proportional to wheel diameter? Weight differences aside, does this mean that bigger wheels actually result in worse suspension performance on fast rough ground? Obviously if that's the case, the benefit of increased rollover from the big wheels must outweigh that effect, since I think we can all agree that bigger wheels feel smoother over chunky terrain despite being heavier too. I just thought it was interesting.
    Nope. The frequency doesn't care about wheel diameter. It only dictates cycles per second.

    Bigger wheels don't change the frequency of the bumps, they can only mute the size of them a little.
    There is only 20mm in radius between 27 and 29" wheels. A hair over 5%. Like virtually everything in this industry the effects are overstated for marketing purposes.
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    Quote Originally Posted by Dougal View Post
    Nope. The frequency doesn't care about wheel diameter. It only dictates cycles per second.

    Bigger wheels don't change the frequency of the bumps, they can only mute the size of them a little.
    There is only 20mm in radius between 27 and 29" wheels. A hair over 5%. Like virtually everything in this industry the effects are overstated for marketing purposes.
    Hmm, I'm having trouble following. When you say frequency, I presume you mean the number of oscillations of the suspension per some amount of time. A bigger wheel encounters the bump sooner and compresses the suspension more slowly over a slightly longer distance, thus lower frequency, no?

    Edit: I suppose if you imagine the bike riding over a succession of bumps at some speed, the bike will always have to travel the same distance to encounter each bump regardless of wheel size. If the wheel is larger, it will hit the first bump sooner, but it will hit the next bump the sooner as well. I guess that's why the frequency won't change?

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    Quote Originally Posted by dlxah View Post
    Edit: I suppose if you imagine the bike riding over a succession of bumps at some speed, the bike will always have to travel the same distance to encounter each bump regardless of wheel size. If the wheel is larger, it will hit the first bump sooner, but it will hit the next bump the sooner as well. I guess that's why the frequency won't change?
    Sounds like you've got it.
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