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  1. #1
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    New bike geometry causing fit problems. Am I the only one?

    I have been looking at new xc bikes and at least on paper not finding a solution. I've been intrigued by the Scott Spark and the Canyon Lux. I've got knee problems that make it critical for me to have good alignment from the pedal axis to the front of my knee. I ride a medium 2015 Pivot M429C with KS dropper(no offset) and my seat is moved as far backwards as possible. This gives me perfect alignment. The STA is 71.9. Newer bikes STA make the seat tube more upright or vertical i.e. ~74. Doing the trig indicates my knee will move forward ~.90". I know this can be solved by an offset seat post or dropper and I like having a dropper. What am I missing or not taking into account? Who besides Giant make an offset dropper?
    TIA
    2015 Pivot Mach 429 Carbon
    2008 Specialized Roubaix Expert

  2. #2
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    The newer geo has moved away from road bike pedaling priorities to maintaining control on downhills and pedaling when on a big angle when climbing. You have an overriding physical requirement. So you'll need to size up to get the correct position. And test ride for a nice long ride.

  3. #3
    Anytime. Anywhere.
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    I don't see how sizing up is gonna help. Get a dropper with setback, 9.8 and Specialized come to mind.
    I got some bad ideas in my head.

  4. #4
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    Not sure if Q Factor will affect your knees as well. I know wider bothers mine. Not sure what a 2015 429 had, but because of boost most frames now seem to be at a min 168mm.
    Just thought I'd mention it since you mentioned knee pain.
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  5. #5
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    what do you mean by "perfect alignment"? I am sorry to break it to you, but if you're setting up your bike by KOPS, that is bullshit that should have been trashed years ago.

    I screwed around with "ideal" pedaling position with the same approach you have for years. 'Twas a red herring in my case. Size the bike by getting the BB and grips in a position relative to one another ( relative reach and stack) and set the saddle that the right height and position so that you're not sliding forward or backward off the saddle.

    That knee alignment stuff make make sense on a tridork bike, but has little significance on a mtb. it's possible that you have significant issues that require a certain position, but have you had that 100% verified by a doctor? it is possible that someone told you that you have you must have that saddle-knee-pedal relationship in a very specific spot, and now that's the idea is in your head, it's stuck there, even though it might not be 100% true without room for compromise? the human body is very adaptable, so could you adapt to a saddle position that's a little further forward? why not move you cleats back a little to compensate? I used to put my cleats right under the ball of my foot, as if I was setting up my feet for an ideal running position. cycling is not running, so that turned out to be nonsense.

    it's possible that you've pigeonholed yourself in a position that is based on a flawed but deeply traditional way of thinking regarding bike fit, and maybe you'd benefit from trying something new.

    again, maybe you've had a doctor verify your knee issues with iron-clad precision measurements. in that case, you need the saddle position and STA that you need. just make sure that is 100% medically sound data before you get fixated on it and toss out 90% of the bikes available on the market based on a possibly flawed premise. I know from personal experience what it's like to be convinced that I "need" to ride my bike a certain way, only to prove myself wrong when I try something new.

    Start by setting up the theoretical BB to handlebar position on Stack and reach calculator and tweak it from there.
    Last edited by mack_turtle; 07-09-2018 at 07:04 AM.
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  6. #6
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    Quote Originally Posted by mack_turtle View Post
    what do you mean by "perfect alignment"? I am sorry to break it to you, but if you're setting up your bike by KOPS, that is bullshit that should have been trashed years ago.

    I screwed around with "ideal" pedaling position with the same approach you have for years. 'Twas a red herring in my case. Size the bike by getting the BB and grips in a position relative to one another ( relative reach and stack) and set the saddle that the right height and position so that you're not sliding forward or backward off the saddle.

    That knee alignment stuff make make sense on a tridork bike, but has little significance on a mtb. it's possible that you have significant issues that require a certain position, but have you had that 100% verified by a doctor? it is possible that someone told you that you have you must have that saddle-knee-pedal relationship in a very specific spot, and now that's the idea is in your head, it's stuck there, even though it might not be 100% true without room for compromise? the human body is very adaptable, so could you adapt to a saddle position that's a little further forward? why not move you cleats back a little to compensate? I used to put my cleats right under the ball of my foot, as if I was setting up my feet for an ideal running position. cycling is not running, so that turned out to be nonsense.

    it's possible that you've pigeonholed yourself in a position that is based on a flawed but deeply traditional way of thinking regarding bike fit, and maybe you'd benefit from trying something new.

    again, maybe you've had a doctor verify your knee issues with iron-clad precision measurements. in that case, you need the saddle position and STA that you need. just make sure that is 100% medically sound data before you get fixated on it and toss out 90% of the bikes available on the market based on a possibly flawed premise. I know from personal experience what it's like to be convinced that I "need" to ride my bike a certain way, only to prove myself wrong when I try something new.

    Start by setting up the theoretical BB to handlebar position on Stack and reach calculator and tweak it from there.
    Trust me, I've played around with a lot of different cleat positions, tried flats, seatposts. I had 6 operations on my left knee and a knee replacement is probably in the future. I had a 2008 Epic with STA of 74 degrees. At the time I had an offset seatpost and bought a dropper with no offset and after a short time started experiencing knee pain. Removed the dropper and knee pain went away. I loved the Epic but it was a 26er and I was in the new bike fever mode. Kind of like now...LOL. Up until that happened I didn't really think about knee to pedal position. I don't stand up and pedal that much these days mostly seated spinning. If I do it's pretty short duration. It's really the seat position to BB position that determines knee to pedal axis and I must have long thighs with a 32" inseam. That's why I posted though was to get differing viewpoints and theories such as yours. I hadn't really ever considered the Q factor mentioned in another post. I don't recall seeing that listed on bike geometries but it is something to consider.
    Cheers
    2015 Pivot Mach 429 Carbon
    2008 Specialized Roubaix Expert

  7. #7
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    The bike fitters that I have been used (Boulder Sports Medicine, among others) don't use KOP per se, but they do pay attention to how far back your saddle is from the BB. If you drop a plumb line from the tip of your saddle (on a bike that fits) and measure how far back on the chain stay, that is a good start. Mine is (plus or minus) 10cm back and that is how all my bikes are setup. So, the protocol the fitters suggest is raise the saddle to the correct height, adjust so you get proper setback re the BB, then adjust stem/bars from the tip of the saddle. Not perfect, but a good reliable start in my experience.

  8. #8
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    Fair enough, sounds like you have thought that through. I just wanted to make sure you didn't get caught up in the same bike fitting dogma nonsense that I did. I had a frame with a 72 degree STA and a 25mm offset post, but the frame fit me just fine otherwise. I don't have particularly long legs, but I was going for that KOPS nonsense.

    Not much else I can tell you that you don't already know. I am under the impression that these steep STA frames are that way to create room for short chainstays and fat tires, overwaise the tire would rub on the seat tube. Most people can work with that, but people with serious knee issue might not.

    However, you might want to dig deeper than the measurements on paper. Some of these frames have bent or offset seat tubes, so the published STA doesn't tell the whole story. You would have to try it on the bike in-person or start emailing each manufacturer with your issue and see if there's a workaround. Hanging the saddle off the end of the rails and a ludicrously long setback is a lousy alternative.
    Last edited by mack_turtle; 07-13-2018 at 01:23 PM.
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  9. #9
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    test ride a few bikes before making a mountain out of what might turn out to be a molehill. there are lots more variables at play than what you've mentioned/accounted for here.

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