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  1. #1
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    why arent chainstay lengths different for different size frames?

    ?????

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    Why doesn't the STA or the HTA change? BB drop?

    Some manufactures do adjust geometry based on size, but not enough IMO.

    I don't have the answer, but it almost certainly has to do with money. Probably they are just saving money on design/engineering.
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  3. #3
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    Quote Originally Posted by nauc View Post
    Why aren't chainstay lengths different for different size frames?
    The short answer is that hey should be. long answer is that manufacturers optimize the bike for the average sized rider and make the bike fit everyone else as cheaply as possible.

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    Norco do this and it makes sense to me. I think partly the "shortest chainstay hype" is to blame and they just build the rear end small as possible then lengthen the front to suit sizing. This puts a small frame rider's weight more rearward and an XL is more forward of centre.

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    Adjustable chainstay length has been around since 2000. Evil did it on their first frame. Others as well. I think Geo and frame Dims is what you shop and demo for. Different types of trail and styles of riding require different fit. 1/4 inch in the chain stay is a big difference. More of a change than a 1/2 inch in BB height. Fore/aft weighting IMO is the most crucial movement on the trail and the one most affected by Chainstay/TT length.

  6. #6
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    chainstay dorsn’t seem to have much room due to wheel size, but it could be done probably just not enough benefit given the price for a new carbon mold or design (leverage ratio and such)

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    That's something I was wondering myself for years, especially people with longer legs have to suffer the most when chainstays are too short since they sit higher and thus have a much higher centre of gravity on a steep incline.

    Theoretically chainstays (= rear-center measurement) should at least grow proportionally to the front-center measurement, in reality they hardly grow at all.

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    Have you measured the chainstays of a bike in its largest and smallest sizes, and are they, in fact, the exact same?
    IDK, but it sure seems that they'd be different if the angles are the same.

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    Quote Originally Posted by Steel Calf View Post
    That's something I was wondering myself for years, especially people with longer legs have to suffer the most when chainstays are too short since they sit higher and thus have a much higher centre of gravity on a steep incline.

    Theoretically chainstays (= rear-center measurement) should at least grow proportionally to the front-center measurement, in reality they hardly grow at all.
    As mentioned, Norco does this. It makes a lot of sense for the reasons you stated.

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    Majority of riders can not tell the difference, and even if they can, unless the stays are really short or really long, it really doesn't make a difference.
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    You can get smaller wheel/tire combos, or you can adjust the offset of the fork to achieve what you need. I wanted smaller wheels, but bigger tires on the Enduro 29. This through off the geo of the 29 in some strange ways. There was enough versatility built into the frame that I was able to "fix" everything, though. The result is a semi-custom bike that is somewhat predictable with my riding style.

  12. #12
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    MTB geo descends from road bike geometry, where they're even more lost. Road bike geometry for tall riders is a mess; wheelbases are 1-2" too short in a realm where it should be really easy to get it right.

    MTB designers have an incentive to sell the same chainstay length to everyone- building one chainstay/BB assembly is more cost effective over a product line, and it's massively easier for warranty. They can tweak seat angle and reach to make a single chainstay length feel right for almost any rider anyway. (it took an uncomfortably long time for production builders to do it- there's no incentive to build good XL frames when bad XL frames sell OK)



    In the end it's rider's perception. Historically riders using 62mm road bikes have had a choice of many shitty road frames... and we adapted to them and they felt normal. We're still getting ourselves accustomed to the idea that a good medium FS bike might be shit in XL. And figuring out that we're getting screwed. It takes time.
    Last edited by scottzg; 06-30-2018 at 05:24 PM.
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    Hmmm... think it all really depends. Lots of times designers are trying to keep the wheelbase as short as possible, ESPECIALLY in the larger sizes, so it wouldn't make any sense to make chainstays longer, except to change the balance of the bike... and really to get that right the larger bikes would need to compromise with steeper HTA AND longer chainstays in order to achieve balance AND handling similar to a smaller frame.

    Long and short of it is NO XL frame is going to handle like a S or M. It can't. It's physics. You could make a S or M handle like a XL, but not many people would buy into that.

    And really it's not a simple equation, there are lots of compounding variables. On some bikes 10mm change in stem or rear wheel position (chainstay length) feels significant. Some it feels inconsequential.

    Unfortunately until someone comes up with a practical way to make the bike geometry adjust bio-mechanically from the feedback of the rider, we're all stuck with some compromise.

    Generally I'd say if you are a big rider and you like long stays, just buy a bike that comes with long stays. Hope it has a steep HTA angle, tiny wheels and short reach (because that's what EVERYONE is doing ) otherwise it's gonna handle like a school bus.
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  14. #14
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    this exact topic was discussed ad nauseum not long ago. I will have to find the old thread.

    Quote Originally Posted by MSU Alum View Post
    Have you measured the chainstays of a bike in its largest and smallest sizes, and are they, in fact, the exact same?
    IDK, but it sure seems that they'd be different if the angles are the same.
    no, I have not measured, but I can read a geometry chart that the manufacturers publishes showing that most frames of the same model change most of the figures on each size except for chainstay length. they have no reason to lie about that.

    yes, I can feel the difference between a bike with a 17" back end and the same bike with a 17.5" back end. all else being equal, it's much easier to get the front end up with the shorter back end.

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    Last edited by tealy; 10-27-2018 at 08:16 AM.
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    Quote Originally Posted by tealy View Post
    Chainstays should be proportional to rider heights. No brainer.

    But so should wheels, crank arms, and handlebar width.

    Yet we see all the time people 5'4" and 6'2" both riding the modern 29er with 175 mm cranks and 780 bars. Makes zero sense to me.

    I'm too lazy to do the math right now, but I bet a 26er/165mm crank/720 bars fits the former person pretty much the same at the latter person on a 29er/180 mm cranks/800 bars. Yet we rarely see wheel/crank/handlebar sizes change with frame size. Sure this makes sense because companies can be be lazy and save money but then result is that in 2018 most people's bikes still don't look like they fit.
    SO by that logic you would say big and tall riders should be on 36" wheels and short riders should be on 20" wheels?

    Have you ever ridden a BMX bike? Also I'd like to see you ride a 36" bike with a 1300mm wheelbase on... welll... pretty much any trail.

    Also you are saying a person with long legs should ride a 175mm crank and short legs a 165? They do that to some degree on some small frames, but if the BB isn't that low to cause pedal strikes you are losing a lot of pedal stroke leverage by running short cranks.

    And I think y'all are missing the bus here... if anything big riders need shorter wheelbase bikes with lower BBs - they have their mass up much higher and have a great disadvantage in terms of having a wheelbase that might match their riding style - unless they just like bombing steeps at high speed.

    On the other end, do small bikes REALLY need shorter wheelbases? They are already plenty agile. There do become some challenges with 29ers and fitting smaller riders due to standover and stack, but many companies offer smaller tires on small or extra small, and I've noticed stop at offering 29ers for sizes under medium. My wife's bike is a 27.5 but in my size it would be a 29er. And we bought that bike 3? years ago. This is not a new thing...
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  17. #17
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    Quote Originally Posted by l'oiseau View Post

    And I think y'all are missing the bus here... if anything big riders need shorter wheelbase bikes with lower BBs - they have their mass up much higher and have a great disadvantage in terms of having a wheelbase that might match their riding style - unless they just like bombing steeps at high speed.
    I'm a 6'3 hobbyist frame builder. Excessively short XL wheelbases were the norm up until what, 3-4 years ago? The size medium frame would be fairly OK, but the big production frames were just horrendously short, by and large. When i'd buy a new frame i'd just scan the geo charts for the longest wheelbase - chainstay length. Having my high mass up where it would tip over the front/rear wheel fulcrum point crippled me; tiny weight shifts translated to huge balance changes. Wheelie to the top of the hill so i could OTB on the way down.

    With new school geometry there are bikes whose length hampers me on narrower trails, but then i'm choosing to compromise on that vs stability. I'm big; i'm accustomed to having to compromise to get myself through small places.

    Quote Originally Posted by l'oiseau View Post

    Generally I'd say if you are a big rider and you like long stays, just buy a bike that comes with long stays. Hope it has a steep HTA angle, tiny wheels and short reach (because that's what EVERYONE is doing ) otherwise it's gonna handle like a school bus.
    Tall riders have gotten used to having the handlebars in their laps, along with short stays. They balance out. If the front end is long enough a long rear end works awesome. The opposite of what you suggest. Anyone half-interested in this should get a bike with horizontal/sliding dropouts to experiment with.

    Quote Originally Posted by tealy View Post
    Chainstays should be proportional to rider heights. No brainer.

    But so should wheels, crank arms, and handlebar width.

    Yet we see all the time people 5'4" and 6'2" both riding the modern 29er with 175 mm cranks and 780 bars. Makes zero sense to me.
    I agree with your logic, but don't agree in practice. If humans walk in a group the taller ones will hitch up our strides and the short ones stretch their steps so our footfalls match. It happens subconsciously, supposedly via the same mechanism that enables us to enjoy music...? Anyway, short people tend to take longer steps, and pedaling is the same. It seems to only be a major issue when the crank length falls outside what the anatomy can do comfortably.

    With handlebars it's similar; the handlebar is tied in to the steering geometry, along with the stem/fork/wheel/frame. You can't slap on a narrow handlebar and be done, so in a production setting it makes sense to keep all the bars as wide as is comfortable for everyone.

    With a custom bike you could go nuts with this... but who wants to deviate from the well-worn path?
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  18. #18
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    Quote Originally Posted by Black Squirrel View Post
    Majority of riders can not tell the difference, and even if they can, unless the stays are really short or really long, it really doesn't make a difference.

    Quote Originally Posted by mack_turtle View Post
    yes, I can feel the difference between a bike with a 17" back end and the same bike with a 17.5" back end. all else being equal, it's much easier to get the front end up with the shorter back end.

    Mack, I mean no offense here, but I'm assuming that this is speculation? I can't imagine the situation where you have two identical bikes except for a 1/2" difference in cs length and have actually confirmed that there is a difference in the ride.

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    Quote Originally Posted by ctxcrossx View Post
    Mack, I mean no offense here, but I'm assuming that this is speculation? I can't imagine the situation where you have two identical bikes except for a 1/2" difference in cs length and have actually confirmed that there is a difference in the ride.
    As i mentioned- sliding/horizontal drops. I can feel a 2mm change; 2mm too short at the short extreme with no other changes and my cornering goes to shit. I notice jumping too, but it's a timing thing that i adapt to quickly. (I think my tallness is a factor in my sensitivity. Also, i'm not that adaptable; i learn a body motion for a specific situation and repeat it. Changing the bike or learning a new high-risk feature is almost going in blind for me. Sucks.)
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    Quote Originally Posted by scottzg View Post
    As i mentioned- sliding/horizontal drops. I can feel a 2mm change; 2mm too short at the short extreme with no other changes and my cornering goes to shit. I notice jumping too, but it's a timing thing that i adapt to quickly. (I think my tallness is a factor in my sensitivity. Also, i'm not that adaptable; i learn a body motion for a specific situation and repeat it. Changing the bike or learning a new high-risk feature is almost going in blind for me. Sucks.)
    Oh yeah. I should have connected the dots on that one. Thanks for the clarification.

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    Last edited by tealy; 10-27-2018 at 08:15 AM.
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    Quote Originally Posted by ctxcrossx View Post
    Mack, I mean no offense here, but I'm assuming that this is speculation? I can't imagine the situation where you have two identical bikes except for a 1/2" difference in cs length and have actually confirmed that there is a difference in the ride.
    I have ridden singlespeeds almost exclusively for the past ten years. they have all had some sort of adjustable dropout with at least one inch of adjustment. I tried adding a link to my chain, using different gear combos (the same ratio but different numbers of teeth on the front/rear). if I ride a 32/20 with the shortest possible dropout setting, then add a link, the effective CS length ends up being about 1/2" longer. I can definitely feel the difference.

    scary moment- I changed the gearing on my old 26" Monocog so that the axle was able to slam forward into the front of the dropout. the position shortened the CS by 1/4 or 1/2". I sat on the bike, rolled down the driveway onto a flat section of road and tried to manual. immediately looped out and almost died because I was clipped in. somehow clipped out in time and hurt my ankle. I was not ready for how different that <1/2" change would feel.

  23. #23
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    Quote Originally Posted by scottzg View Post
    I'm a 6'3 hobbyist frame builder. Excessively short XL wheelbases were the norm up until what, 3-4 years ago? The size medium frame would be fairly OK, but the big production frames were just horrendously short, by and large. When i'd buy a new frame i'd just scan the geo charts for the longest wheelbase - chainstay length. Having my high mass up where it would tip over the front/rear wheel fulcrum point crippled me; tiny weight shifts translated to huge balance changes. Wheelie to the top of the hill so i could OTB on the way down.

    With new school geometry there are bikes whose length hampers me on narrower trails, but then i'm choosing to compromise on that vs stability. I'm big; i'm accustomed to having to compromise to get myself through small places.



    Tall riders have gotten used to having the handlebars in their laps, along with short stays. They balance out. If the front end is long enough a long rear end works awesome. The opposite of what you suggest. Anyone half-interested in this should get a bike with horizontal/sliding dropouts to experiment with.



    I agree with your logic, but don't agree in practice. If humans walk in a group the taller ones will hitch up our strides and the short ones stretch their steps so our footfalls match. It happens subconsciously, supposedly via the same mechanism that enables us to enjoy music...? Anyway, short people tend to take longer steps, and pedaling is the same. It seems to only be a major issue when the crank length falls outside what the anatomy can do comfortably.

    With handlebars it's similar; the handlebar is tied in to the steering geometry, along with the stem/fork/wheel/frame. You can't slap on a narrow handlebar and be done, so in a production setting it makes sense to keep all the bars as wide as is comfortable for everyone.

    With a custom bike you could go nuts with this... but who wants to deviate from the well-worn path?
    Well put.

    My anecdote to add to the pot is that when I jumped on the 29" bandwagon years back my first 29" bikes were a ??? HT from Bikes Direct followed by a Spesh Stumpjumper HT with both bikes being built up identically. While the Stumpy overall rode nicer the ??? BD had 1 cm longer chain stays and was a far better climber. I don't remember if the ??? BD was also 1 cm longer in WB or not but the point is that CS length 1/2" one way or the other is very noticeable.

    I think a big reason most Mfg's keep CS length the same through a model's size range is "economies of scale"; it simply keeps the production costs down.
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    Quote Originally Posted by l'oiseau View Post
    Hmmm... think it all really depends. Lots of times designers are trying to keep the wheelbase as short as possible, ESPECIALLY in the larger sizes, so it wouldn't make any sense to make chainstays longer, except to change the balance of the bike... and really to get that right the larger bikes would need to compromise with steeper HTA AND longer chainstays in order to achieve balance AND handling similar to a smaller frame.

    Long and short of it is NO XL frame is going to handle like a S or M. It can't. It's physics. You could make a S or M handle like a XL, but not many people would buy into that.

    And really it's not a simple equation, there are lots of compounding variables. On some bikes 10mm change in stem or rear wheel position (chainstay length) feels significant. Some it feels inconsequential.

    Unfortunately until someone comes up with a practical way to make the bike geometry adjust bio-mechanically from the feedback of the rider, we're all stuck with some compromise.

    Generally I'd say if you are a big rider and you like long stays, just buy a bike that comes with long stays. Hope it has a steep HTA angle, tiny wheels and short reach (because that's what EVERYONE is doing ) otherwise it's gonna handle like a school bus.
    ^^^I think this is the closest answer.

    The short limit on chainstays hasn't been reached since 26ers were common, so nobody - alright, most riders would rather not go longer. Hence the big frames are probably fine, while the small frames probably have too long of a chainstay compared to a 26er that probably provides a better fit for the rider. The compromise is probably worth it to ride bigger wheels, though.

    And yes, 1/4" of bottom bracket or CS length is completely noticeable within 5 minutes of riding (or less).

    -F

    PS - I will concede that maybe in the XL-XXL sizes and adjustment might be appropriate. maybe.
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    Surely, if a large-scale manufacturer can create necessary different length head tubes, top tubes, seat stays, etc... basically every tube on every bike has different dimensions for each size, they could tweak chainstay lengths for the sizes if they thought it would optimize handling.

    either there is something the designers know about keeping CS lengths the same across sizes that we don't, or some other force - marketing or manufacturing costs - is holding this back.

    I'd be curious to hear a custom frame builders' perspective. If one were to build two frames for a pair of friends with similar riding styles and the same.local trails, but one of the friends is 8" taller than the other, what dimwnsions would change between the two frames?

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    I'm sure it's coming, it wasn't as practical in the days of aluminum manufacture, where it was probably cheaper to manufacture FS rear ends in one size and bolt them up. Now with carbon frames being made as a mold, one size frame doesn't really have anything to do with the next size, so this will probably become standard at some time. Some company will offer this on their entire line some year when they've run out of other innovations and the industry and this website will make them out to be heros and it'll spread to all the other manufacturers.
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    Quote Originally Posted by Jayem View Post
    ... it was probably cheaper to manufacture FS rear ends in one size and bolt them up.
    fair point. I am usually thinking in terms of hardtails though. it seems like any model will have different sized tubes for everything but the bottom bracket, so why not make proportional chainstays? if I were extremely tall, I can see how I might have a hard time with a short back end. perhaps the front-center and rear-center should change proportionately.

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    Quote Originally Posted by mack_turtle View Post
    Surely, if a large-scale manufacturer can create necessary different length head tubes, top tubes, seat stays, etc... basically every tube on every bike has different dimensions for each size, they could tweak chainstay lengths for the sizes if they thought it would optimize handling.

    either there is something the designers know about keeping CS lengths the same across sizes that we don't, or some other force - marketing or manufacturing costs - is holding this back.

    I'd be curious to hear a custom frame builders' perspective. If one were to build two frames for a pair of friends with similar riding styles and the same.local trails, but one of the friends is 8" taller than the other, what dimwnsions would change between the two frames?
    I'm not a frame builder, but I can say from a pure engineering standpoint... it depends

    And I mean that seriously. What size tires does the short rider have? What crank length does each rider prefer? How much travel F/R, if any? What does each rider ride?

    All those things will affect how one might optimize a frame.

    I really don't buy the whole "manufacturers are evil" and they are doing it to save cost. It doesn't make sense from a handling standpoint or design standpoint, because they can and will change every other tube on the bike (as was mentioned, some which don't affect handling at all).

    I think it's more the fact that generally large riders don't want longer than need to be wheelbases. It's as simple as that. Many already complain that current 29ers are too long.

    Another thought experiment is this... a lot frames that have a 27.5/29 analog will use the same CS length. Why is that? Obviously they could go shorter for a 27.5... and hint, it's not manufacturing because almost all use different stay designs/yokes for tire clearance.
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    Quote Originally Posted by Jayem View Post
    I'm sure it's coming, it wasn't as practical in the days of aluminum manufacture, where it was probably cheaper to manufacture FS rear ends in one size and bolt them up. Now with carbon frames being made as a mold, one size frame doesn't really have anything to do with the next size, so this will probably become standard at some time. Some company will offer this on their entire line some year when they've run out of other innovations and the industry and this website will make them out to be heros and it'll spread to all the other manufacturers.
    Dang. That was a long thought. Thanks!

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    I would suggest that any man taller than 6' and any woman taller than 5' 8" look into a professional bike fitting if they are having any fit issues whatsoever. (I would recommend this for anyone who is having a hard time finding a comfortable and efficient riding position.)

    Many taller riders are much better served by getting a custom bike.

    Now, about those 10' basketball hoops for short guys who can't jump...
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    Quote Originally Posted by mack_turtle View Post
    Surely, if a large-scale manufacturer can create necessary different length head tubes, top tubes, seat stays, etc... basically every tube on every bike has different dimensions for each size, they could tweak chainstay lengths for the sizes if they thought it would optimize handling.

    either there is something the designers know about keeping CS lengths the same across sizes that we don't, or some other force - marketing or manufacturing costs - is holding this back.
    Marketing. There's been a dick-waving contest in the industry over the last while to see who can stuff the shortest possible chainstays on their bikes without having the rear tire hit something. The DH world has figured out that this is stupid and started lengthening out their rear ends again for better stability & handling, with a few exceptions, the rest of the industry is still clueless and stuck on the "shorter stays is better" bandwagon.

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    Quote Originally Posted by djlee View Post
    I would suggest that any man taller than 6' and any woman taller than 5' 8" look into a professional bike fitting if they are having any fit issues whatsoever. (I would recommend this for anyone who is having a hard time finding a comfortable and efficient riding position.)
    I am not sure how this applies to the static (on most bikes) chainstay length. if you buy a bike and the chainstay is X mm long, no amount of moving the contact points around is going to help the fact that X is too long to allow you to get the front end up consistently, or too short to help you keep the front end down, and that sort of thing. if you're talking about a custom frame built around your dimensions, that's different, but $$$$.

    my experience with bike fitters has been meh. most of them put your mountain bike on a trainer and set you up for a great position to pedal on level ground in a straight line. it's difficult or impossible to extrapolate how a bike fit that way will handle once it's leaned into a corner or hucked up/ down an incline.

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    Quote Originally Posted by aerius View Post
    Marketing. There's been a dick-waving contest in the industry over the last while to see who can stuff the shortest possible chainstays on their bikes without having the rear tire hit something.
    this is true, except when it's not. there are many bikes that have long-ish chainstays, often bikes with lots of rear travel or XC race bikes. that does not explain why a XC bike for a person who is 6'2" has the exact same CS length (whether you can consider it long or short) as the same model sized for someone who is 5'2". for example, Specialized makes two versions of the Chisel, men and women. both models across all sizes have a 430mm chainstay.

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    Quote Originally Posted by mack_turtle View Post
    I am not sure how this applies to the static (on most bikes) chainstay length. if you buy a bike and the chainstay is X mm long, no amount of moving the contact points around is going to help the fact that X is too long to allow you to get the front end up consistently, or too short to help you keep the front end down, and that sort of thing. if you're talking about a custom frame built around your dimensions, that's different, but $$$$.

    my experience with bike fitters has been meh. most of them put your mountain bike on a trainer and set you up for a great position to pedal on level ground in a straight line. it's difficult or impossible to extrapolate how a bike fit that way will handle once it's leaned into a corner or hucked up/ down an incline.
    I agree with part of your opinion of most bike fitters in general - they tend to be more road oriented. There are some very knowledgeable mountain bike fitters out there. I guess it depends on where you live.

    My comment was more directed towards custom frames for tall people. Yes, they are pricey, but not really any more than carbon.

    You are right about this not applying to the static chainstay length of most manufacturers, though.
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    As mentioned:

    “Traditional frame designs disregard rear-center lengths when changing size, leading to sub-optimal riding positions for some riders. Gravity Tune fixes the front-centre/rear-centre ratio across all frame sizes, effectively optimizing geometry and rider weight distribution for every bike in the line.”

    why arent chainstay lengths different for different size frames?-24a518c0-84a6-480f-ad94-aec4dc0114bb.jpg

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    Quote Originally Posted by aerius View Post
    Marketing. There's been a dick-waving contest in the industry over the last while to see who can stuff the shortest possible chainstays on their bikes without having the rear tire hit something. The DH world has figured out that this is stupid and started lengthening out their rear ends again for better stability & handling, with a few exceptions, the rest of the industry is still clueless and stuck on the "shorter stays is better" bandwagon.
    I think the long-ish chainstay "thing" only works in DH because of the momentum/speed and steepness of the course. The same design criteria applied to an XC or AM bike won't work as well in tighter, slower turns, and probably leaves something to be desired in climbing and slow tech.

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    why arent chainstay lengths different for different size frames?

    Manufacturer have a tendency to create a new segment (and take the credit) each time they make a slight change to a geometry (think CX vs Gravel), so can you imagine if they change the chain stay for all the different frame sizes ?


    We would be flooded by a multitude of new segment and new forums

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    Quote Originally Posted by mack_turtle View Post
    this exact topic was discussed ad nauseum not long ago. I will have to find the old thread.



    no, I have not measured, but I can read a geometry chart that the manufacturers publishes showing that most frames of the same model change most of the figures on each size except for chainstay length. they have no reason to lie about that.

    yes, I can feel the difference between a bike with a 17" back end and the same bike with a 17.5" back end. all else being equal, it's much easier to get the front end up with the shorter back end.
    So I'm guessing they do this by having the same rear triangle for an XS as for an XL?
    I don't actually give a sh*t - I don't make my purchase decisions based on this measure - I'm just curious.

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    I'm sure it's been mentioned but IMO cost is number 1. Most everything else on a frame is proportional. If you took an image of a small frame and zoomed 30%, the chain stays would be longer.
    I got some bad ideas in my head.

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    Quote Originally Posted by Fleas View Post
    I think the long-ish chainstay "thing" only works in DH because of the momentum/speed and steepness of the course. The same design criteria applied to an XC or AM bike won't work as well in tighter, slower turns, and probably leaves something to be desired in climbing and slow tech.

    -F
    Based on my experimentation with the sliding dropouts on my hardtail trail bike, a chainstay length that's a bit longer than industry standards works best for everything except pulling wheelies. For many years, the standard chainstay length was 425mm for a 26" wheel hardtail, every Kona, Rocky Mountain, or Norco I owned was 425. And they handled pretty well. About 6 years ago I bought a 2006 Kona with sliding dropouts and spent the next couple years experimenting with different chainstay lengths, I started at 425mm just like the rest of my bikes then went to the extremes and everything in between.

    I eventually settled in at a bit over 430mm, it gives a bit better stability with almost no loss in agility, but surprisingly it made a huge improvement in climbing. When standing & climbing, it keeps the front end down a lot better and the rear tire doesn't break traction or spin out as much, it's especially noticeable on loose surfaces or when I need to get the rear tire over stuff on a climb, it doesn't spin or get hung up as much. Going longer does improve stability but it also starts killing the agility pretty quickly and climbing doesn't improve any further, shorter is fun for pump tracks but too tail happy for my taste on the trails.

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    Quote Originally Posted by aerius View Post
    Based on my experimentation with the sliding dropouts on my hardtail trail bike, a chainstay length that's a bit longer than industry standards works best for everything except pulling wheelies. For many years, the standard chainstay length was 425mm for a 26" wheel hardtail, every Kona, Rocky Mountain, or Norco I owned was 425. And they handled pretty well. About 6 years ago I bought a 2006 Kona with sliding dropouts and spent the next couple years experimenting with different chainstay lengths, I started at 425mm just like the rest of my bikes then went to the extremes and everything in between.

    I eventually settled in at a bit over 430mm, it gives a bit better stability with almost no loss in agility, but surprisingly it made a huge improvement in climbing. When standing & climbing, it keeps the front end down a lot better and the rear tire doesn't break traction or spin out as much, it's especially noticeable on loose surfaces or when I need to get the rear tire over stuff on a climb, it doesn't spin or get hung up as much. Going longer does improve stability but it also starts killing the agility pretty quickly and climbing doesn't improve any further, shorter is fun for pump tracks but too tail happy for my taste on the trails.
    ^^^This is a good data point.
    But note that few current bikes are anywhere near 430mm CS's, so the desire to get there - or get as close as they can - means that longer is generally undesirable (or compromising to other features). My Nimble9 is at about 16.4" (416mm). I would not go longer since my frame of reference on CS length is from my old 26er StumpJumper.

    If 430mm is the "ideal" for a small frame, should the XXL frame CS's be 460? I can't help but think the ideal number is smaller than 430, esp. for smaller riders, but the size of the rear wheel simply won't allow it. That leads me to believe that the longest anyone would want in any size is not much more than 430.

    And some of that stability comes from steering geo. and wheel base.

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    Quote Originally Posted by Fleas View Post
    ^^^This is a good data point.
    But note that few current bikes are anywhere near 430mm CS's, so the desire to get there - or get as close as they can - means that longer is generally undesirable (or compromising to other features). My Nimble9 is at about 16.4" (416mm). I would not go longer since my frame of reference on CS length is from my old 26er StumpJumper.

    If 430mm is the "ideal" for a small frame, should the XXL frame CS's be 460? I can't help but think the ideal number is smaller than 430, esp. for smaller riders, but the size of the rear wheel simply won't allow it. That leads me to believe that the longest anyone would want in any size is not much more than 430.

    And some of that stability comes from steering geo. and wheel base.

    -F
    I've done this a bit as well. I can definitely feel a 10-12 mm change is CS length. It's mostly how the bike lifts the front end though. I don't feel any high speed stability or change in handling.

    Now changing the front end numbers, which usually results in a much bigger than 10 mm change in wheelbase, I REALLY feel the handling. I'm sure I'd feel it in the rear end too if I could change the wheelbase by 25+mm from the rear.

    430 seems to be a target for manufacturers with FS. For hardtails they'll go shorter, because they can. I've ridden 416 and 420 and I don't notice a huge difference there. Once you are that short I believe it's just a pissing match between manufacturers.

    There's a number of 27.5 and 26 bikes of old that could have gone much shorter, and some did (Cannondale BOE Gen 1?) and I don't think it turned to be very good. The resulting loss in climbing ability most likely trumped any return in front end lift or rear end response.
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    Short answer is they should be.
    Long answer is it adds cost and complexity to manufacturing and parts availability.
    Most medium 29ers have perfect chain stay length (CSL). CSL is to long for smalls and to short for larger and up. By the time you get to an XXL like I ride, CSL is so out of wack it FUBAR's the handling.
    You simply can't add 100mm of front center to a bike and keep the same CSL without introducing compromises somewhere. Shorter offset forks are part of this trend to give the longer reach bikes shorter front centers. I swapped from 51 to 44 fork and it made a noticeable difference in feel. My 505 reach bike has a 432 rear and I wish it was 445-450.

    My old XL blur XC carbon has 421mm CSL and it severely limits how steep of a hill I can climb.
    Last edited by alexbn921; 07-06-2018 at 12:22 PM.
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    Quote Originally Posted by alexbn921 View Post
    Short answer is they should be.
    Long answer is it adds cost and complexity to manufacturing and parts arability.
    Most medium 29ers have perfect chain stay length (CSL). CSL is to long for smalls and to short for larger and up. By the time you get to an XXL like I ride, CSL is so out of wack it FUBAR's the handling.
    You simply can't add 100mm of front center to a bike and keep the same CSL without introducing compromises somewhere. Shorter offset forks are part of this trend to give the longer reach bikes shorter front centers. I swapped from 51 to 44 fork and it made a noticeable difference in feel. My 505 reach bike has a 432 rear and I wish it was 445-450.

    My old XL blur XC carbon has 421mm CSL and it severely limits how steep of a hill I can climb.
    ^^^This all sounds perfectly reasonable.

    For a comparison, we used to ride up a concrete drainage between a lower and an upper parking lot. This was ~1992. Not sure how short/long the old RockHopper's stays were, but this climb was pretty much the steepest anyone could do on a bike. Unlimited traction. No bumps. Just gear down and go up. Front tire barely touching - like riding a wheelie - requiring even pedal strokes and centered body. I was a bit lighter then, though, so COG was probably lower. I still think that if my chainstay is at least as long as that bike, then I'm good to go. But I don't find value in going much longer.

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    okay
    Last edited by tealy; 10-27-2018 at 08:13 AM.
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    Quote Originally Posted by tealy View Post
    I agree that short-as-possible chainstays are the current fad, but I'm all about it. I want a bike that easy to manual. Period.

    For flat-out downhill speed and stability, I agree that longer stays are better.

    But for everything else, I think shorter is generally better. The bike is stronger and lighter. Easier to manual, wheelie, turn, and climb. To me that equals fun.
    I generally agree with this, at least with respect to the terrain I usually ride. The differences are especially contrasted in more technical terrain, such as Moab, where wheelie drops are often not optional. I hate having to exert myself just to lift my front tire off the ground.

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    Quote Originally Posted by tealy View Post
    I agree that short-as-possible chainstays are the current fad, but I'm all about it. I want a bike that easy to manual. Period.

    For flat-out downhill speed and stability, I agree that longer stays are better.

    But for everything else, I think shorter is generally better. The bike is stronger and lighter. Easier to manual, wheelie, turn, and climb. To me that equals fun.
    What size bike do you ride? This makes a big difference in preferred CSL.
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    OK naysayers. Explain this one:

    https://americaneagle.online/atlanta-2-0-dutch-orange/

    High end, XC racing frame. Carbon, so separate molds for every bike anyway. Everything is different except BB drop and CS length for every frame size, including HTA and STA.

    Why?

    The answer is not cost.
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    Quote Originally Posted by l'oiseau View Post
    OK naysayers. Explain this one:

    https://americaneagle.online/atlanta-2-0-dutch-orange/

    High end, XC racing frame. Carbon, so separate molds for every bike anyway. Everything is different except BB drop and CS length for every frame size, including HTA and STA.

    Why?

    The answer is not cost.
    Maybe they're stuck in the dark ages.

    This bike is currently being raced in UCI World Cup XC competition where it's finished in the top 15.
    https://www.norco.com/bikes/mountain...volver-ht-xx1/

    It uses a different chainstay length for each size, as does the full suspension version of the frame.

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    Quote Originally Posted by aerius View Post
    Maybe they're stuck in the dark ages.

    This bike is currently being raced in UCI World Cup XC competition where it's finished in the top 15.
    https://www.norco.com/bikes/mountain...volver-ht-xx1/

    It uses a different chainstay length for each size, as does the full suspension version of the frame.
    Top 15? That's cute. That bike won the women's overall last year. Shall we pull up the geo for the current leaders and last years winners overall and world champ?

    So is your point that it doesn't matter? Because if it really did, wouldn't they just be winning everything? Or at least attracting a rider that could?

    Also does any one person's result prove that there is an advantage for a small rider vs a large rider for changing stay length?

    And one other thing... a Cannondale Lefty is typically on the podium in the UCI XC WC, does that mean they are a good design with any specific advantage over a conventional fork which is ALWAYS on the podium?

    My example proves that is not done for manufacturing or cost because none of those apply to that specific frame I linked. Being a molded hardtail, they could have easily changed the stay length on the medium and the large. The only reason I picked a WC race frame is because cost is not an issue on these. They'll do whatever they want and it costs what it costs.
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    Quote Originally Posted by aerius View Post
    Maybe they're stuck in the dark ages.

    This bike is currently being raced in UCI World Cup XC competition where it's finished in the top 15.
    https://www.norco.com/bikes/mountain...volver-ht-xx1/

    It uses a different chainstay length for each size, as does the full suspension version of the frame.
    Uuuhhhggg. That bike has a 1.5 degree steeper HTA in XL than XS. No thank you.
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    Quote Originally Posted by l'oiseau View Post
    OK naysayers. Explain this one:

    https://americaneagle.online/atlanta-2-0-dutch-orange/

    High end, XC racing frame. Carbon, so separate molds for every bike anyway. Everything is different except BB drop and CS length for every frame size, including HTA and STA.

    Why?

    The answer is not cost.
    Good point.

    -it's easier for consumers to understand a single chainstay length. It might handle different for different size riders, but we don't change sizes and know what a given length feels like even if it's different for someone else.

    -the designer can tweak the front triangle and the user can tweak the cockpit for a suboptimal chainstay length to work

    -really tall/short people have adapted to wonky geometry. Unfamiliar is always initially bad.

    -design convention is to preserve those elements across the size run; it's more risky to scale the chainstays and have to convince the customer it's a good thing

    -some designers don't understand what it's like to be dramatically taller or shorter than them

    -XC racers do some seriously goofy cockpit stuff, it's hard to dial in CS length when the rider is gonna mount a 25* stem upside down

    -cost. Cost is always a factor.



    That bike has a 2" shorter wheelbase than what i'd want for XC racing.
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    I subscribe to the idea that CSL should be proportional to the overall frame size.

    You only need to do a quick analysis across frame sizes to see the front/rear centre bias changes a fair bit.

    Granted some might not notice but I certainly do and it helped point me towards the Banshee Prime in XL which has adjustable drop outs for this reason. The CSL is actually quite long too.

    Having tried the Santa Cruz Hightower LT in XL I can categorically say I'm not a fan of short chain stays and Santa Cruz themselves admitted they wish size specific rear centres was something the wish they'd done.

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    Quote Originally Posted by scottzg View Post
    Good point.

    -it's easier for consumers to understand a single chainstay length. It might handle different for different size riders, but we don't change sizes and know what a given length feels like even if it's different for someone else.

    -the designer can tweak the front triangle and the user can tweak the cockpit for a suboptimal chainstay length to work

    -really tall/short people have adapted to wonky geometry. Unfamiliar is always initially bad.

    -design convention is to preserve those elements across the size run; it's more risky to scale the chainstays and have to convince the customer it's a good thing

    -some designers don't understand what it's like to be dramatically taller or shorter than them

    -XC racers do some seriously goofy cockpit stuff, it's hard to dial in CS length when the rider is gonna mount a 25* stem upside down

    -cost. Cost is always a factor.



    That bike has a 2" shorter wheelbase than what i'd want for XC racing.
    Doesn't come in in XL

    I don't buy your analysis on CSL being suboptimal for the rider. If you look at WC frame geometry across womens and mens top riders you'll see there is a pretty big spread (about 15mm). There's also a number of large and small riders all on these geometries and they all seem to be "optimal" for the rider.

    None of them besides that new Norco could I find an example where they changed CSL for any size.

    I'm not saying the designers are right or wrong here, but simply put, if there was a clear advantage, and there is a decent sample size of riders with long and and short CS with different body sizes, wouldn't we see some difference in performance?

    Cost? Have you seen what WC XC bike costs? They aren't exactly cutting any corners to keep it down.
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    Quote Originally Posted by JonJones View Post
    Having tried the Santa Cruz Hightower LT in XL I can categorically say I'm not a fan of short chain stays and Santa Cruz themselves admitted they wish size specific rear centres was something the wish they'd done.
    Putting short chainstays on an otherwise unchanged design/frame doesn't necessarily improve the ride, or work well in general. Other manufacturers have short chainstay geometry dialed in quite well. It's usually paired with a steeper STA, lower BB, Longer reach, and slacker HTA.

    Writing off short chainstays based on one bad experience is a pretty narrow minded way of analyzing bike geo. Likewise what you personally prefer and works for you on your local trails may not be ideal for others on different terrain with a different riding style.
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    Quote Originally Posted by *OneSpeed* View Post
    [short chainstay] usually paired with a steeper STA, lower BB, Longer reach, and slacker HTA.
    it seems that the steep STA is often required to make a shorter chainstay work, to keep the tire from hitting the seat tube. which is the real reason for these super-steep seat tubes? if it's a compromise that works, fine. let's not confuse a design feature that was made for functional reasons for something that optimizes geometry.

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    It's a key part of the bigger picture IMO. If you shorten the rear end you need to get more weight forward or you'll never be able to keep the front end down when climbing. The extra tire clearance is a by-product of the (necessary) steeper STA.

    It's all relative and it depends on how short of a chainstay we're talking about, but the lower BB and longer TT also help keep the front end down.
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    Quote Originally Posted by tealy View Post
    For flat-out downhill speed and stability, I agree that longer stays are better.

    But for everything else, I think shorter is generally better. The bike is stronger and lighter. Easier to manual, wheelie, turn, and climb. To me that equals fun.
    After I got over the shock of agreeing with tealy I came back here to post how correct this is. In 2015 I had to adapt to a short CS bike, but it didn't take long. Now every time I ride my old Blur or get on someone's 'stable' bike I'm surprised anyone would prefer it. The climbs around here are short, but they're steep enough I have to adjust my stance, too forward and back tire slips, too little and front tire lifts. The range MIGHT be shorter than the old bike, but it's well worth it. New geo bikes are way fun, and the faster you go; the more you have to flick them over to make a corner, the more you realize these geometry changes are an improvement. Improvement for Trail bikes ridden on twisty, pedally trails anyway.
    oops I wasn't clipped in

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    CSL are designed around medium bikes.
    Unless you are riding an XS or XL/XXL bike, you haven't really experienced how Fubared geometry can get. My XXL is 100mm longer in the front than a small. Try taking out or adding 50mm to your chain stays and tell my how your bike handles.
    It's important to include you bike size in this discussion or we have no frame of reference.
    I'm 6'4" and ride an XXL. 99% of chain stays are to short for me. 99% of XL bike are to small too, so there's that.
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    Quote Originally Posted by alexbn921 View Post
    Try taking out or adding 50mm to your chain stays and tell my how your bike handles.
    It's important to include you bike size in this discussion or we have no frame of reference.
    This must be one of those times it's good to be average. I know this sounds a bit dickish, and I don't like to be that way. Try re-reading your sig-line. What I mean is I have/ride medium and small frames, some work a little better for me in one way or another, but I adapt to what I'm on.
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    Not dickish at all. It's good to be average height. Being in the 99 percentile makes life much harder than it should be. I wasn't trying to be dickish either, just pointing that how big you are directly influences your perspective on CSL.
    I'm also a little bitter, after riding bikes too small for me for my entire life. It has taken me years to figure out bike fit/balance and sucks that we are forced to ride around poor design. Bikes are getting so much better, but there is still room for improvement especially on the CSL.
    Making shit harder than it needs to be isn't awesome, it's just...harder.

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    Quote Originally Posted by alexbn921 View Post
    Not dickish at all. It's good to be average height. Being in the 99 percentile makes life much harder than it should be. I wasn't trying to be dickish either, just pointing that how big you are directly influences your perspective on CSL.
    I'm also a little bitter, after riding bikes too small for me for my entire life. It has taken me years to figure out bike fit/balance and sucks that we are forced to ride around poor design. Bikes are getting so much better, but there is still room for improvement especially on the CSL.
    I couldn't agree more.
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    Quote Originally Posted by alexbn921 View Post
    Uuuhhhggg. That bike has a 1.5 degree steeper HTA in XL than XS. No thank you.
    And there's a reason for that. What happens when you go from an XS to XL frame? For one thing the bike gets a lot longer, the wheelbase on the XL is 100mm longer than the XS and this is going to have a pretty big impact on the handling of the bike. If the HTA were the same on both bikes, the XL would be significantly more stable at speed than the XS while giving up a fair amount of low speed agility. How do we compensate for that? Slacken out the HTA on the XS to give it more stability and steepen the HTA on the XL a bit to restore its handling in tighter, lower speed trails.

    IMO this is the right way to do things but it still doesn't go far enough. Everything should be adjusted as needed so that the feel & handling of the bike is consistent across all sizes. The BB height can also be changed across the size range, smaller sizes have shorter cranks so we can lower the BB a bit to improve stability.

    With almost all bikes these days, we have folks going up a size or down a size for more stability or more agility, respectively. This means that a given model of bike doesn't handle consistently across the size range, a rider on a small frame isn't having the same experience as a rider on an XL. As noted a few posts above, if you're riding a medium size frame you're getting the experience that the manufacturer intended you to have. If you're riding a small or XL, you're getting something pretty different. I think that needs to change.

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    Couldnt agree more here.

    Problem is that it's exceptionally difficult to do because many will still not be completely happy. Thankfully there is so many options out there. Also custom build options.

    There is still more than that messing with things. All of which I think has been mentioned at some point.

    I've ridden enough to learn some things. Not to mention geometry and physics 101 create major issues.

    An XS framed bike is going to be way faster in tight and twisty over an XL. Optimal turning radius on an XL is a good bit larger. Add in rider size difference and that's more mass your trying to change directions of.

    Wheel/tire size plays a part too. I ride and XL 27.5+ yet watch large and medium 29ers sometimes (and even much more so 29+ struggle with a more advanced rider than me) not able keep up with me in the tight and twisty.

    There is a lot to all this.

    But one thing I have watched pretty well:

    Short chain stays and longer fronts are the way to go like it's some big thing. But truly it does NOTHING but shift rider weight backwards. All that has happened is to shifter the riders COG in relationship to the bike. Yet I see so many say how different it all is. Yet wheelbase is about the same if not slightly longer due to slackened HTA. Other changes have played a part like lower BB and things like that which can have huge effects. But the matter of short chain stays making some huge difference when TT is lengthened along with it, there is no real difference in that aspect beyond where your weight on the bike (rearward bias for going down hill).

    Personally though I like having the same short stays as the smaller frames. I'm yet to go OTB on my b+ bike bought new last year. Weight is heavily rear bias which is nice. Took some tweaking to get decent cornering in the tight stuff so I wasnt getting left behind.

    I think my BIGGEST COMPLAINT. The whole BB height thing. XL getting no increase. 5mm goes a LONG WAY lol.


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    Last edited by RAKC Ind; 07-10-2018 at 11:23 AM.
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  65. #65
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    YT Capra has longer stays on the larger models.

  66. #66
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    So here's another thing I don't get...

    When two frames from different manufacturers have been "optimized" for a "medium" rider with nearly the same front end geometry and one with 435mm stays and the other with 420, how does one optimize for larger and smaller riders?

    Seems to me it's just ride preference, and a large rider may prefer the short rear end just as much depending on his personal preferences.

    BTW these "frames" are purely hypothetical, but I'm sure I could pull up some that would fit this general description that were manufactured in the last 5 years.
    Life is too short to ride a bike you don't love.

  67. #67
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    Quote Originally Posted by l'oiseau View Post
    So here's another thing I don't get...

    When two frames from different manufacturers have been "optimized" for a "medium" rider with nearly the same front end geometry and one with 435mm stays and the other with 420, how does one optimize for larger and smaller riders?
    Easy, we bring back 26" wheels!

  68. #68
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    Quote Originally Posted by JonJones View Post
    Having tried the Santa Cruz Hightower LT in XL I can categorically say I'm not a fan of short chain stays
    438mm is longer than most and part of the reason I chose the HTLT. What bike do you have that has stays longer than 438mm?

  69. #69
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    Most seat stays are the minimum that manufactures can fit with linkage design and tire clearance. That size is then the "Optimized" size they sell.
    Long travel 29ers require longer stays just to clear the tire, unless you do something seriously funky.
    Seated max climbing angle would be a great way to quantity CSL. Lets say you can climb a 30% slope on a medium bike before tipping over and this gives a nice playful feeling bike. With all the angles and CSL the same, a XL bike can only climb a 20% slope. Making the chain-stays longer until the XL rider can climb the same 30% slope will give a similar feel in manualing the bike. In fact it would still be easier for the taller ride with there longer legs/arms.
    Making shit harder than it needs to be isn't awesome, it's just...harder.

  70. #70
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    Quote Originally Posted by mack_turtle View Post
    it seems that the steep STA is often required to make a shorter chainstay work, to keep the tire from hitting the seat tube. which is the real reason for these super-steep seat tubes? if it's a compromise that works, fine. let's not confuse a design feature that was made for functional reasons for something that optimizes geometry.
    For me the move to steeper STA has been a great improvement over my previous geometry, so I welcome the trend. For me, and probably some others, it does optimize geometry.
    I got some bad ideas in my head.

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