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  1. #1
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    MTB Geometry - What the hell does it al mean???

    So I'm checking out a few medium to long travel 29'ers in the hopes of figuring our what my next ride should be. I'm currently riding an XL (21.5) Trek Top Fuel, but would like something burlier. Have had a chance to demo and rent a half a dozen different bikes over the course of this last year and I'm finally starting to look into the geometry of the bikes I've been riding.

    I recently demoed a L Pivot Switchblade and was blown away by the bike. It has a longer wheelbase but shorter chainstays than my current bike. I didn't think a bike in this category could feel both smoother on rough descents AND snappier/more responsive cornering. I'm guessing this is due to the wheelbase and stay lengths.

    Wondering how much weight everyone puts into the geo's of the mtn bikes they check out. Do you look at a bike's numbers first and say to yourself, "I think that bike could work for me"? In other words, can you really predict how a bike will feel based on the numbers? Or is this a short-sighted way to look at it?

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    I chose what bikes to,test ride based on the numbers. Then test rode. Then decided what I liked. Ended up with a GG smash. Laid up with a knee injury right now but pavement test on my new bike so far so good

  3. #3
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    Both. Look at the numbers, while remembering that you may be surprised. But that's within reason, and mostly within category. For example, a big bike like a Wreckoning might pedal and handle much better than you'd expect based on specs, but it's not a XC bike.

  4. #4
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    yes and no. If you know what you like, you can make a pretty good guesstimation of how it will handle and fit by geocharts. But things like leverage ratios and suspension curves, etc. don't compute to me, so I have to ride it to see how the suspension behaves in real life, coupled with the geo. If I'm buying a new bike, I'm going to demo it first, if at all possible. They are too expensive to guess IMO.

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    Quote Originally Posted by d365 View Post
    yes and no. If you know what you like, you can make a pretty good guesstimation of how it will handle and fit by geocharts. But things like leverage ratios and suspension curves, etc. don't compute to me, so I have to ride it to see how the suspension behaves in real life, coupled with the geo. If I'm buying a new bike, I'm going to demo it first, if at all possible. They are too expensive to guess IMO.
    Yup, similar bikes to the Switchback. Are the Canfield riot and GG Smash. All 3 will feel different, I was between the switch back and Riot, for fit. Picked the Riot for the higher bottom bracket, for less pedal strikes and changing directions quickly.

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    For a rider like the OP on a Top Fuel there are a number of steps when you are looking at more travel. I'd include the v2 Following if the sizing works depending on the trails you ride. More technical short turn trails versus longer park runs means one bike over another.

  7. #7
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    OP, to answer your question, yes. A person familiar enough with bike geo can look at the numbers and tell how it will handle. I've purchased my last 5 bikes without a test ride and been happy. I've also had a couple custom frames built and worked with the builders to get the geo right (that's how I learned about geo). But I wouldn't recommend going this route unless you really understand what you're doing.

    Also as d365 mentioned above, if it's a full suspension bike you're going for, you won't know how the suspension will feel until you ride it. Buying an undemo'd FS bike is truly a leap of faith for those of us not neck deep into it.
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  8. #8
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    Personally, I have learned to kind of understand geo and the effects it might have on the ride of a bike, but it's not 100% and it's mostly all I have to go on as I live where there's really no bike shops to demo bikes from, so have to go on geo and reviews. If I lived someplace that I could easily demo bikes, I'd skip looking at the geo of the bikes and just go ride them, pick which one felt best to me, then I'd look at the geo so I knew what I had and what in the future might work, which seems to be about what you've done.
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  9. #9
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    If you've ridden a lot of bikes and are capable of thinking methodically, then yes you can tell a lot about how a bike is going to ride without riding it. You can certainly tell if/how it's going to fit based on comparison to bikes you've sat on and know how they fit.

    I'm assuming you're on the tall side; it's not like you're going to be able to test ride bikes anyway. In 28 years of riding, I've seen one bike my size on a shop floor, available to demo (and a total of zero shops willing to get a bike for me to try without committing to buy it). If you're over 6' you pretty much have to figure out how to do this without a shop.

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    What type of numbers are you guys looking for?

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    Quote Originally Posted by Joules View Post
    If you've ridden a lot of bikes and are capable of thinking methodically, then yes you can tell a lot about how a bike is going to ride without riding it. You can certainly tell if/how it's going to fit based on comparison to bikes you've sat on and know how they fit.

    I'm assuming you're on the tall side; it's not like you're going to be able to test ride bikes anyway. In 28 years of riding, I've seen one bike my size on a shop floor, available to demo (and a total of zero shops willing to get a bike for me to try without committing to buy it). If you're over 6' you pretty much have to figure out how to do this without a shop.
    Actually I'm just 6' tall but have ape arms and around a 35" inseam. Beginning to think I may be happier in a bike that I can size down to large assuming the seat tube can handle my legs.

  12. #12
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    Quote Originally Posted by d365 View Post
    yes and no. If you know what you like, you can make a pretty good guesstimation of how it will handle and fit by geocharts. But things like leverage ratios and suspension curves, etc. don't compute to me, so I have to ride it to see how the suspension behaves in real life, coupled with the geo. If I'm buying a new bike, I'm going to demo it first, if at all possible. They are too expensive to guess IMO.
    If you don't mind me asking, what sort of things do you like?

  13. #13
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    I think if I have a bike and I like the way it rides, it usually is a function of the reach/stack and the chainstay length/headtube angle/fork offset. Finding bikes with similar measurements will almost always result and a feeling of familiarity when I first get on the bike, which translates to confidence on the trail. The confidence is not always accurate though, because so much of how a bike actually handles depends on handlebars/suspension/tires etc... geometry will paint the big picture, the components will fill in the details.

    Here's how I look at the geometry numbers:

    ST LENGTH - how long is the seat tupe from center of bb to top of seat tube. Tells me if my fancy new dropper post is going to work.

    TT LENGTH - how far from the seat to the head tube, this is how far the handlebars are when your ass is in the saddle.

    REACH - this estimates how far you are from the handlebars when you are standing up. Modern geometry has made this longer, along with a shorter stem and wider handlebars.

    STACK – An imaginary line from the bottom bracket to the end of the reach. This, along with reach, for mountain bikes will define how the bike will feel when riding. Now how it will handle necessarily, but how it will feel. Stack too low and you will feel bent over, and have back pain, stack too tall and you will feel like you’re on a beach cruiser. Stack and reach too tall? Get a smaller size.

    STANDOVER- if you mess up in the parking lot, will your crotch hit the top tube?

    HT ANGLE - big deal in modern geometry, slacker is better because it means less chance of supremanning over your bars into a tree. Makes you feel fast downhill, too slack (think 65 degrees or so, makes tight switch backs really difficult. Learn how to do nose wheelies. Think of your favorite ride, have a lot of 180 degree turns? Probalby dont want too slack of a head tube, maybe 67 degrees. Anything over 70 and expect a call from the 90s, they want their bike back, that or your riding a road bike.

    HT LENGTH – The length of your headtube. Female riders will tell you it’s not important, just that it has a flared base to add to the stiffness. There is a kernel of truth to that, but 4” is probably the low end of headtube length you want.

    ST ANGLE – these days steeper seems to be more in fashion. This affects how powerful your pedal strokes will feel when sitting down.

    CS LENGTH – shorter is better, up to a limit. Shorter stays will make the front of the bike easier to move around while riding: manuals, bunny hops, etc… The downside is that on the uphills, when you’re pedaling, your front wheel may decide it wants to go make out with that bush, and there’s nothing you can do about it. Longer chainstays can make a bike feel more stable, but harder to do fun things on.

    BB DROP – draw a line between your axles, then measure the distance from that line to your bottom bracket, that’s drop. More drop (along with appropriate reach and stack) will make you feel like you are riding inside the bike, rather than on top. It’s a hard feeling to describe, but it makes cornering feel easier. Too much drop and you will experience constant pedal strikes.

    BB HEIGHT – the counter point to bb-drop, but it measures from the ground up to the bottom bracket. This can change significantly depending on tire choice. General consensus seems to be that BB height (and drop) should result in the bb as low as your riding conditions/style can accommodate. Trails with more rocks roots, maybe higher to prevent pedal strikes (or shorter crank arms), smooth(er) trails, maybe a bit lower.

    WHEELBASE – This depends on chainstay length and headtube angle and fork length etc… but generally a long wheelbase will make a bike feel long and stable. I think 1200mm is a good threshold, bike with wheelbases longer than that will feel (to me) ungainly on the trail.

    FRONT CENTER – I’m not entirely sure why this one matters, it seems like stack, reach head tube angle, fork offset would cover this.

    FORK LENGTH- how long your fork is.

    FORK OFFSET (Rake/Trail) – Rake is how offset the axle is from the steering axis. This is what makes a bike feel twitchy or comfortable in the corners. Rake ultimately affects trail, which is a function of rake and headtube angle. Too much trail makes a bike feel “lazy” in the turns, too little makes your bike feel twitchy.
    Last edited by dompedro3; 09-12-2017 at 08:06 AM. Reason: make it more readable

  14. #14
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    Delay gratification and ride bikes.

    I surely knew the basics of what slack, low bb, short chain stays and fork off set do but even but having a similar Remedy 29 and new gen Fuel EX still found differences. That's with same type of suspension.

    Now to what Sparticus said. A friend's Hightower has a lot in common with my Fuel EX as far as geometry and 140 mm forks but the VPP suspension and Trek's Penske magic shock create personality differences. Same with my trying similar bikes that are Horst type or basic single pivot.

    You want to ride the bikes so you can sort out stuff like the value or performance you get if the frame is made from recycled beer cans or plastic. It was a total eye opener for me to ride and then have a same model bike with the different frame materials.

    Ride different bikes to know how much you want to spend on wheels. My wife and I have same tires on a bike with basic OEM and higher level wheels. We feel that difference more than we do with more expensive frames.

    The good news is I happen to feel most all the known bike makers have good stuff these days.

    My first steps for shopping has been making a spreadsheet that has geometry of current bike(s), past bikes and what interests us.

    To the OP's points, I can know that 65-66 degree front with any offset is a different animal than 68-69 degrees. I know our Kona's rather extreme short chain stays make some climbs more difficult than the Remedy 29's length with a new Fuel EX a happy medium. I know I could care less about those who whine about low bottom brackets. I ride greased sharp rocks and roots considering those pedal banks as just cold forging my crank ends. The bike's too much fun to give up.

    It took me a season of trying and renting to happily move from heirloom wheels to big ones. It took me 60 seconds to know a the Top Fuel and similar are for grunting out a race. The only grunting I put up with on a regular basis is is for making turds. I don't do XC races and don't want bikes that feel like your job is grunting out a turd.
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    Quote Originally Posted by dompedro3 View Post
    STACK – An imaginary line from the bottom bracket to the end of the reach. This, along with reach, for mountain bikes will define how the bike will feel when riding. Now how it will handle necessarily, but how it will feel. Stack too low and you will feel bent over, and have back pain, stack too tall and you will feel like you’re on a beach cruiser. Stack and reach too tall? Get a smaller size.

    STANDOVER- if you mess up in the parking lot, will your crotch hit the top tube?
    These are the two I've been trying to wrap my head around, especially the stack.

  16. #16
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    Quote Originally Posted by bitflogger View Post
    Delay gratification and ride bikes.

    I surely knew the basics of what slack, low bb, short chain stays and fork off set do but even but having a similar Remedy 29 and new gen Fuel EX still found differences. That's with same type of suspension.
    I've ridden both the 2017 Remedy (27.5) and 2017 Fuel EX. Been considering the Fuel EX or Slash (which looks to have pretty similar geo to EX). In your experience how does the Trek sizing compare with other manufacturers? I've only ridden 21.5's in Treks as my LBS seemed to think this was the best frame size for me. After riding the L Switchblade, I'm wondering if I could size down to a 19.5 in an EX or Slash to get a little more playfulness out of the bike.

  17. #17
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    Quote Originally Posted by eman555 View Post
    I've ridden both the 2017 Remedy (27.5) and 2017 Fuel EX. Been considering the Fuel EX or Slash (which looks to have pretty similar geo to EX). In your experience how does the Trek sizing compare with other manufacturers? I've only ridden 21.5's in Treks as my LBS seemed to think this was the best frame size for me. After riding the L Switchblade, I'm wondering if I could size down to a 19.5 in an EX or Slash to get a little more playfulness out of the bike.
    We have different Treks in 17.5, 18.5, 19, and 20. They all work. I'm 5'10" and shrinking. I like the 18.5 FEX w/ short stem.

    You have to test or ride them. Same height friends dislike my setup as much as I love it.
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    I think of standover as the old way of estimating what stack actually measures.
    Think of riding your bike in an attack position (standing). Your legs, your upper body and your arms make a rough angle, reach + stack is how bikes these days approximate that. The reach is the horizontal measurement, the stack is the vertical. Too short or long of either will result in back pain (IME)

    There will be a reach/stack combinations that are comfortable for you, and ones that are faster, and they may not intersect. By identifying what your ideal reach/stack range is you can estimate how you will feel on a bike before you ride it.

    Being comfortable does not necesarily mean the bike will ride well, just that it's geometry is well suited to your body type/riding posture. A bike will not ride well if you are uncomfortable, so get that established first, then start dialing in how you want the bike to ride ("playful", steering feel, climbing while seated, climbing while standing etc...)

    Honestly, standover is a way to make people feel comfortable in a showroom on a particular bike, and since a key part of selling something is to have people hold it in their hands (between their legs for a bike), having bikes that assault ones crotch in the showroom is not a good way to sell it. How do you actually dismount the bike on the trail, how often do you suddenly straddle your top tube with your feet on the ground? Often the bike is leaning to one side, significantly lowering it's standover.

  19. #19
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    I'm just a newbie to mtb riding , when I bought my last bike, I sat down with different companies geo charts and made a bunch of drawings to scale.
    this way I had them all laid out in front of me, I found it easier to compare models and
    degrees when they were all laid out on paper. I could compare them side to side

    easier to see if you sit more forward on this,or that, where your weight center would be
    between different models
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  20. #20
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    Quote Originally Posted by d365 View Post
    If you know what you like, you can make a pretty good guesstimation of how it will handle and fit by geocharts. But things like leverage ratios and suspension curves, etc. don't compute to me, so I have to ride it to see how the suspension behaves in real life, coupled with the geo. If I'm buying a new bike, I'm going to demo it first, if at all possible.
    Totally agree. I can pick a rigid bike without demoing, but full suspension is another thing. Even if you get a demo, and dial in fit, and dial in suspension, you still usually get but one ride on one trail with parts you didn't choose. Online reviews help. I demoed for years until I got a 4-day demo with my current full-suspension bike. Will keep it until the frame breaks!
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    x1000 on a full squish. My current FS is a 2015 RIP 9. By the time I bought it, the whole longer/lower/slacker thing was already well under way. Comparatively the Niner had a relatively tall stack, short TT, long stays, and a steep HA. It was all just very WRONG according the current trail bike lore. If I listened to the numbers alone, it should have been a turd. Yet on the trail it's a killer. It pops, it climbs, it turns, it goes downhill, and does it all predictably and beautifully. Had I disqualified it on the numbers alone, I'd have missed out on a great bike. So understand the numbers....and understand the numbers alone does not a great bike make.

  22. #22
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    Provincial, what do you think of your Switchblade? Just demoed one and loved it.

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    I like it, bought it at the beginning of june,
    so far all of the components and frame have held up well. I try to ride 3 times a week

    but like I said, I only started in April of this year on the local mountain bike trails
    so I don't have much to compare it too
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  24. #24
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    Quote Originally Posted by eman555 View Post
    Provincial, what do you think of your Switchblade? Just demoed one and loved it.
    See, agonizing over geocharts is for people who can't just go demo it... demoing always tells the real story.

    Geocharts are pretty meaningless, unless you know what you like and need ahead of time, and only if you understand what the numbers are telling you, and how they affect the ride. The only way to gain this comparative knowledge is to ride bikes, and try to understand why it rides/fits like it does in correlation to its geo numbers.

    BUT>>>> You loved riding the Switchblade... that is really all you need to know to make an informed purchase! Go ride a few others and see how they stack up.

  25. #25
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    Quote Originally Posted by d365 View Post
    BUT>>>> You loved riding the Switchblade... that is really all you need to know to make an informed purchase! Go ride a few others and see how they stack up.
    Thanks, working on it!

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