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  1. #1
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    Why do we accept single chainstay length across sizes?

    Virtually any dimension of a frame changes with it's sizing. Chainstay length is the obvious exception here. On a 29-er where you can't go shorter anyway it's no problem, but why do we accept this on smaller wheeled bikes?

    Course, you have some room to play with the seat position, but you can't both properly position a size S rider and a XL rider with the same chainstay length without causing unwanted side-effects on both sides of the spectrum.

    You see medium sized reviewers raving about chainstay length's that has XL riders slide the seat too far forward causing a suboptimal body position with too much pressure on the wrists and you see renowned bike builders adopting overly large rear ends to suit their larger riders, but compromising the handling of the smaller sizes in the process.

    The solution is simple, one chainstay length for the medium size and smaller and one for the L size and larger. You won't need more than that, two length's is sufficient to enable a proper body position on all sizes. As a side effect you can reduce the reach jump a little between the M and L sizes so less people are in between sizes for the most populated part of the rider size curve.

    Sure it would cost a bit more for the bike manufacturers because you have two suspension designs to tune, but to me the extra cost seems far more justifiable than the few grams you save on say a drivetrain upgrade.
    Last edited by CS645; 12-26-2014 at 09:44 AM.

  2. #2
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    Quote Originally Posted by CS645 View Post

    Sure it would cost a bit more for the bike manufacturers because you have two suspension designs to tune, but to me the extra cost seems far more valuable that the few grams you save on a drive train upgrade.
    While we're at it, why don't they make different shock leverage ratios for different sizes? We know the guy on the XL is gonna weigh more than the guy on the small.

    Poor cost:benefit ratio for manufacturer.



    Some savvy manufacturers change something else (front triangle geo or shock valving, in these examples) to compensate for it.
    .

  3. #3
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    Quote Originally Posted by scottzg View Post
    While we're at it, why don't they make different shock leverage ratios for different sizes? We know the guy on the XL is gonna weigh more than the guy on the small.
    Indeed.

    Poor cost:benefit ratio for manufacturer.

    Some savvy manufacturers change something else (front triangle geo or shock valving, in these examples) to compensate for it.
    I think the cost:benefit ratio is poor because we accept it and rather invest in bling bling than a properly sized bike. I reckon this is a task for bike journalism to make the average rider more aware so the cost:benefit ratio becomes more favourable. Although most reviewers are roughly M or L sized so they don't really have this issue.

  4. #4
    Anytime. Anywhere.
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    Norco is doing this, check out the Range.

    Range Carbon - Enduro - Mountain - Bikes - Norco Bicycles
    I got some bad ideas in my head.

  5. #5
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    Quote Originally Posted by Travis Bickle View Post
    Norco is doing this, check out the Range.

    Range Carbon - Enduro - Mountain - Bikes - Norco Bicycles
    Kudo's to them.

    You wouldn't even need 4 sizes like Norco's does it. Two length's with 8mm or so in between would be sufficient.

  6. #6
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    I have seen 29ers that range from close to 16" to 18" chainstays. Shorter is not always better on any wheel size. I would think that bigger frames ought to have slightly longer chainstays on every bike, but some tall riders might prefer the flickability of super short chainstays and some shorter riders might prefer the stability of longer stays. Manufacturers ought to make their chainstays longer on bigger sizes if they want the same ride quality from each model on each size for riders of all heights. At this point, I am all for adjustable dropouts, since riding style and a rider's body size may vary among riders of the same height.

    So, I agree.

  7. #7
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    Shorter chainstays are almost always better for mountain biking. If you built a bike around 24" wheels, then it might be beneficial to adjust the chainstay length. For 26" wheels and larger, it's usually already longer than most riders, tall or short, prefer.

  8. #8
    Singletrackmac
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    Same reason you don't get a different BB height or HT angle between different size bikes. The chain stay length changes the handling characteristics of the bike, like the ht angle and BB. It doesn't have anything to do with rider fit, like the seat tube, TT or HT height.

    Longer chain stays are good for stability at speed just like a slack HA, while shorter chain stays are good for maneuverability, manuals and tight cornering just like a steeper HA.

    I am 6'4" and wouldn't want a longer chainstay than the shortest possible a bike could fit on my trail bike, but on a DH bike I want a longer chainstay for stability.

    My size has nothing to do with it, it's the type of riding that determines how long the chain stay should be.
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  9. #9
    Old Fart Swamper
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    Chain stay length, slacker HT angles, seat tube angles to name a few, all this or that.

    I've now been on a number of different bikes and I can feel differences in all these specs but still nothing changes as I will always buy after a good test ride then tune the fit and just learn that bike.

    I don't worry with all that.

    I've been on several Treks I really like,
    Now on my second Scott, yeah It serves me well.
    Tried a Specialized carbon once, real nice.
    Tried three Giants and didn't like a single one, no Idea why.
    Rode a Raleigh and a Diamondback, they were awful..

    It's all personal choice and as said In several posts the makers do what they do to turn a profit. Companies must compete to win or they die.

    OP go find a bike you like, buy it and ride the snot out of it.
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  10. #10
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    I don't position my saddle in relation to the rear wheel so this doesn't make any sense to me. I suppose taller riders on bigger frames will be positioned further back relative to the rear axle when seated, but so what? I've never had any problems with that on size large frames except maybe my old Santa Cruz Bullitt that liked to loft the front wheel on steeper seated climbs. But it was the short rear with the slack front that made the bike fun on the downhills. So please don't lengthen the chainstay on bigger frames. If you want it that way, go custom.

  11. #11
    Old Fart Swamper
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    Quote Originally Posted by Thor29 View Post
    So please don't lengthen the chainstay on bigger frames. If you want it that way, go custom.
    Err ya go, well said :P
    Scott Spark 760
    I no longer clip In,
    got a better seat, and a dropper post.
    Other than It's Bone stock.
    It Just works :P

  12. #12
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    As others have said, is it much simpler to manufacture the same rear triangle across the board or have 4 different sizes? Obviously, making the same triangle across the board is much cheaper option.

    Norco is one of the few manufacturers that have different rear triangle for different frames. In addition to rear triangle, they also increase tube profile for larger size bikes. They call it "size scaled" fit.

  13. #13
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    My bianchi road bike has chainstay length scaled up for the larger size, as does my on-one 456. (Both hardtail frames, obviously, where there's no rear suspension setup to tune or build on a separate jig) It doesn't take much; 2-3mm per size has a very noticeable effect on how the bike tracks uphill and allows a more reasonable bar height. How the bike balances isn't necessarily changed. (i'm 6'3)

    The answers in this thread kinda illustrate why it doesn't make sense to make size-specific chainstays; there's not much consensus on the need.
    .

  14. #14
    The White Jeff W
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    Adjustable dropouts are available on many bikes and give the rider the ability to set CS length where they want without altering rider position. Seems like a good reltively low cost option to me.

    This set-up on a Ventana gives over an inch +/-

    Why do we accept single chainstay length across sizes?-thumblarge-3.jpg
    No moss...

  15. #15
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    Quote Originally Posted by singletrackmack View Post
    Same reason you don't get a different BB height or HT angle between different size bikes. The chain stay length changes the handling characteristics of the bike, like the ht angle and BB. It doesn't have anything to do with rider fit, like the seat tube, TT or HT height.

    Longer chain stays are good for stability at speed just like a slack HA, while shorter chain stays are good for maneuverability, manuals and tight cornering just like a steeper HA.

    I am 6'4" and wouldn't want a longer chainstay than the shortest possible a bike could fit on my trail bike, but on a DH bike I want a longer chainstay for stability.

    My size has nothing to do with it, it's the type of riding that determines how long the chain stay should be.
    Dissagree, chain stay length is related too both handling and sizing just like TT length.

    If you want a bike that climbs steadily with the front wheel planted you need a longer chainstays to prevent a tall rider to be over the back wheel too much. That's just simple physics. Just like a smaller rider doesn't need longer chainstays.

    So sure, chainstay length influences handling, but so does TT length and we don't keep that the same for all sizes either.

    I'm not saying that all chainstays should be longer, but that it should be determined by size AND the designers handling philosophy and not by something arbitrary like cost. If you want a playful bike you choose a brand that rates playfulness over a planted climbing feel and you'll still get plenty short chainstays.

    Further advantage could be that the smaller sizes get 170mm cranks with the BB lowered 5mm and the larger ones get 175mm.

  16. #16
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    Quote Originally Posted by CS645 View Post
    Dissagree, chain stay length is related too both handling and sizing just like TT length.

    If you want a bike that climbs steadily with the front wheel planted you need a longer chainstays to prevent a tall rider to be over the back wheel too much. That's just simple physics. Just like a smaller rider doesn't need longer chainstays.

    So sure, chainstay length influences handling, but so does TT length and we don't keep that the same for all sizes either.
    TT length is longer for larger frames because taller bikers have longer arms and this has to do directly with rider fit. I am 6'3 and if I had to have a TT the same length as a small frame that would make for one very cramped, and uncomfortable ride that would send me over the handlebars. The TT length is increased as the size of the bike goes up not to change the handling characteristics between sizes, but to keep it keep it the same between sizes.

    Also, you are wrong about needing a longer chain-stay to keep the front wheel planted and steady while climbing for taller riders. Bike manufactures have had a solution to this since the 80's, they increase the seat angle by a degree or so on larger frame sizes. They could increase the chain-stay length instead, but like Mack says, that would change the bikes handling characteristics. I, and I would think almost all MTBRs, would much rather have a bike with a steeper seat angle to improve the climbing if needed and maintain handling characteristics than a longer chain-stay that would degrade the handling.

    I would never buy a bike that had a longer chain-stay for the XL size. Why would you want a bike that doesn't handle as good as the smaller sizes when you can just increase the seat angle to fix any issues with climbing? This is why almost no bike companies have longer chain stays for bigger frames, it's not because of cost.

  17. #17
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    Different TT lengths between sizes are indeed to properly fit different sized riders. Obviously no disagreement there, but if you are seriously suggesting that a longer TT and thus a longer wheelbase doesn't affect the handling of a bike than the last bit of usefulness of our discussion is out of the window. The whole forward geometry from Mondraker is based around a lengthened top tube and it's beneficiary effect on handling (to some).

    As said before, steeper seat angles do help to keep the front wheel planted, but at some point the side effects of this, for instance too much pressure on the wrists, are unwanted. For some this is a compromise they are willing to accept for the sake of playful handling and for other's it is not. For people who like long days in the saddle with a lot of climbing, not just quick rides in the backyards or shuttle assisted rides, this is in general is more important.

    To each his own, let's just agree to disagree.

  18. #18
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    Quote Originally Posted by tahoebeau View Post
    I would never buy a bike that had a longer chain-stay for the XL size. Why would you want a bike that doesn't handle as good as the smaller sizes when you can just increase the seat angle to fix any issues with climbing? This is why almost no bike companies have longer chain stays for bigger frames, it's not because of cost.
    More like "why would you make a bike that already handles worse handle even more poorly" The XL framed bikes are already a good deal longer than the size S bikes.

    Bike designers try to build a bike with a given personality. Extending the rear of the bike along with the necessary extension of the front will result in a totally different bike. There's lots of variation in CS length amongst the different manufacturers. Test ride them as said above and choose what you like. The reason you don't see the variation in a given model is as noted: cost and effect on handling characteristics.

  19. #19
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    I'm 189 cm (6'2") with a 92 cm (36") inseam. So my saddle is quite high, but I lean forward on a properly sized bike, which retains a good weight distribution between the wheels. When mashing uphill I shift weight forward to keep the front wheel down, and if the chainstays were longer I'd lose grip in the rear and ability to lift or lighten the front end easily when going over obstacles.

    A stern "no" from me to varying chainstay lengths depending on size. However, it would be a good thing to have "something for everyone", so a manufacturer could have a different model with longer chainstays available in all sizes. Or adjustabe ones, that's cool too.

    Just don't assume taller people will automatically need longer chainstays. It isn't so.

  20. #20
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    Quote Originally Posted by jeffw-13 View Post
    Adjustable dropouts are available on many bikes and give the rider the ability to set CS length where they want without altering rider position. Seems like a good reltively low cost option to me.

    This set-up on a Ventana gives over an inch +/-

    Click image for larger version. 

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    I agree that having adjustable dropouts is a great solution. For race bikes, where a goal is to make bikes as light as possible, this might not be optimal, but for the "average" bike it's a great idea.

    To me the idea that "shorter stays are always better" is not correct. I've owned several frames with adjustable stays and I've not always chosen to run the stays "short." The bike that I'm riding right now has the stays adjusted to be nearly as long as possible. In the snow and on icy trails, the longer wheelbase offers better stability, and also with the longer stays it's easier to "sit and spin" up a hill without worrying about the front end lifting.

    Another advantage of adjustable stays is the ability to adjust the stays based on the tire size. When I run over-sized nobbies I adjust the stays to be longer giving me more clearance, and with less aggressive tires I can make the stays shorter (if desired).

    Keep, in my mind, for any given seat tube angle, as the saddle height is raised the saddle is also moved rearward. The longer the rider's legs are the more rearward the saddle is positioned, and therefore when seated the weight is more biased toward the rear of the bike. Super short stays with a very high saddle could put the rider's weight behind the rear axle (try pulling a wheelie on a kid's bike and see how easy it is to land on your backside). When seated, it would make sense to have longer stays on larger frames to keep weight distribution the same. However, I'm not sure what the impact on weight distribution is when standing (and the weight moves from the saddle to the pedals).

    But as others have said, different manufactures opt for different chain stays lengths because not everyone thinks that "shorter is better." Adjustable dropouts let you choose the stay length that works for you and vary it based on riding condition - that's a nice feature.
    Each bicycle owned exponentially increases the probability that none is working correctly.

  21. #21
    Jon
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    That is why I buy custom frames, (CUSTOM GEOMETRY) it makes or breaks the feel of the bike and I have exceptionally long legs. I also like short chain stays and long top tubes for a lighter front end.

    I have to add that my Standard DJ bike has slotted drop outs along with deraiuer hanger and diks mounts. I can adjust things pretty far and use several disk options that way also.
    Man I hope someone brought TP.

  22. #22
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    thought experiment: how much body english does an average weight 5'6" rider on an appropriately-fit "small" frame have to employ to, let's say, loft the front wheel of a bicycle. is the same effort required to clear the same obstacle for a 6'4" rider of average weight for his size on an appropriately-fit extra-large frame if both frames have the same chainstay length? I am genuinely curious.

    I would think that the taller rider would be more likely to loop out while the shorter rider would have to exert himself greatly to achieve the same maneuver. that assumes a lot of variables, but a higher center of gravity would give the taller rider a more flickable bike and the lower CoG of the shorter rider a more stable bike. given that these frames are the same model with different stack-and-reach measurements, the static chainstay length would yield a different experience for different size riders.

    ergo: the chainstay on the larger frames should be a little longer if the want designer wants the handling characteristics to remain the same across a model's size run.

  23. #23
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    CS645, about half your posts are about frame design, including the bikecad link in your signature. Whats your story? I don't think you're gonna have much luck bringing anyone around to your way of thinking, unfortunately.

    Quote Originally Posted by jeffw-13 View Post
    Adjustable dropouts are available on many bikes and give the rider the ability to set CS length where they want without altering rider position. Seems like a good relatively low cost option to me.

    This set-up on a Ventana gives over an inch +/-

    Click image for larger version. 

Name:	thumblarge-3.jpg 
Views:	89 
Size:	202.2 KB 
ID:	950449
    I bet those dropouts cost about 150$ per pair wholesale. Not really that low cost. Awesome though.
    .

  24. #24
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    Quote Originally Posted by laffeaux View Post
    Keep, in my mind, for any given seat tube angle, as the saddle height is raised the saddle is also moved rearward. The longer the rider's legs are the more rearward the saddle is positioned, and therefore when seated the weight is more biased toward the rear of the bike.
    --
    When seated, it would make sense to have longer stays on larger frames to keep weight distribution the same. However, I'm not sure what the impact on weight distribution is when standing (and the weight moves from the saddle to the pedals).
    Unless only the legs are longer, the above is not true. A taller rider has longer legs, but also a longer torso and arms. Sure, the butt moves back as the saddle is raised, but the head of the rider moves forward along with extended reach, as bike sizes go up. The result is a balanced weight distribution just like shorter people have.

    If a tall person has too much weight on the rear wheel, chainstay length or saddle adjustment is not the problem. The best solution is to use a longer stem or frame to shift some weight to the front wheel.

  25. #25
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    6'4" been riding XL FS bikes for many years. I like the trend for steeper ST angles. CS length isn't going to be my first geometry go to number - Stack, reach, BB height etc.

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