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  1. #1
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    Relationship Between 1cm In Saddle Height And Knee Angle/Flexion

    My last fit has me at a knee angle of 146 degrees or a knee flexion of 34 degrees. The reason I'm a bit low is mostly due to a previous low back injury. After a year and some months riding like this I'd like to experiment with moving the saddle higher to try and extract a touch more power.

    I doubt it is possible to say moving the saddle 1cm will change the angle by X degrees due to anatomical variation. But wondering if there are any rough rules of thumb so-to-speak or perhaps a formula I'm not aware of to figure this out. I'd like to not go past 155/25. I'm home alone with sick kids and no goniometer. Eventually I'll get in touch with the fitter but thought I'd ask here first.

  2. #2
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    Although 1cm is a small increment, it makes a difference. The previous fit may serve as your benchmark. At the end of the day, the best fitter is still the rider. Try changing the height, and ride it for a while. To be sure, measure your saddle height beforehand so that you have a reference if it doesn't work out.

    Hogg's approach is practical. Good luck.

  3. #3
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    Any reputable fitter I've ever spoken to has always said to make adjustments in 3mm increments and never more than one adjustment at a time. This includes a local guy (who just fit me) who was formally trained by Steve Hogg.

  4. #4
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    Yeah. I can feel a 3mm difference pretty readily. Normally, the knee should be bent about 25 deg at the bottom of the stroke when pedaling normally. I say "when pedaling normally" because how you pedal and the angle at which you hold your foot while pedaling can significantly affect that angle, and it may be different when you look at it statically.
    ... 'cuz that's how I roll.

  5. #5
    wim
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    A 1 cm saddle height change results in about a 0.5 degree change in knee angle at the bottom of the crank circle. You can see this in a chart at page 22 of the .pdf at the link below. With no change in saddle height, knee angle changed by about 2.5 degrees for every 5 cm of crank length change. Lengthening the crank without changing saddle height is equivalent to raising the saddle, so the numbers are valid either way.

    What affects knee angle much more than the relatively small saddle height changes made by an experienced rider is the angular orientation of the pedal with respect to the ground (heel rise / heel drop). With that in mind, knee angle changes from customary saddle height fine-tuning changes are so small that they don't really matter much.

    http://www.arniebakercycling.com/pub...39%20pages.pdf
    Last edited by wim; 01-25-2013 at 11:32 AM.

  6. #6
    FTR
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    Forget about knee angles and hip flexion as a way of fitting yourself unless these measurements were simply coincidental as a result of your fit.

  7. #7
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    Quote Originally Posted by wim View Post
    A 1 cm saddle height change results in about a 0.5 degree change in knee angle at the bottom of the crank circle. You can see this in a chart at page 22 of the .pdf at the link below. With no change in saddle height, knee angle changed by about 2.5 degrees for every 5 cm of crank length change. Lengthening the crank without changing saddle height is equivalent to raising the saddle, so the numbers are valid either way.

    What affects knee angle much more than the relatively small saddle height changes made by an experienced rider is the angular orientation of the pedal with respect to the ground (heel rise / heel drop). With that in mind, knee angle changes from customary saddle height fine-tuning changes are so small that they don't really matter much.

    http://www.arniebakercycling.com/pub...39%20pages.pdf
    That was a great read, thanks for that link.

  8. #8
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    Quote Originally Posted by wim View Post
    A 1 cm saddle height change results in about a 0.5 degree change in knee angle at the bottom of the crank circle. You can see this in a chart at page 22 of the .pdf at the link below. With no change in saddle height, knee angle changed by about 2.5 degrees for every 5 cm of crank length change. Lengthening the crank without changing saddle height is equivalent to raising the saddle, so the numbers are valid either way.

    What affects knee angle much more than the relatively small saddle height changes made by an experienced rider is the angular orientation of the pedal with respect to the ground (heel rise / heel drop). With that in mind, knee angle changes from customary saddle height fine-tuning changes are so small that they don't really matter much.

    http://www.arniebakercycling.com/pub...39%20pages.pdf
    Too funny. I actually read Arnie's article and missed the relationship as it was talking about crank length (pg 22) at least. I think I just skimmed past as I was focused too narrowly on seat height/angle relationship only. Thank you for pointing this out!

    Approximately 1cm seat height=5 degrees knee flexion. bam!

  9. #9
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    Quote Originally Posted by FTR View Post
    Forget about knee angles and hip flexion as a way of fitting yourself unless these measurements were simply coincidental as a result of your fit.
    +1. I'm with you and not trying to get to any angle. Totally coincidental. I do follow Hogg and others. The gent that helped me has done work with him, Cobb an others. Not that this validates him but, his life/business is fitting and teaching others to become fitters. We did a fit when I was getting back on the bike after an injury. I ended up on the low side with respect to knee angle/seat height. I'm roughly at 4.6w/kg and a goal is to try (injury willing) to get to 5w/kg. Just trying to find on my own if a touch more height will generate more wattage. I am a bit nervous about changing anything as the injury is always in the back of my mind. All this is more curiosity and general knowledge than anything else.

  10. #10
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    Quote Originally Posted by FTR View Post
    Forget about knee angles and hip flexion as a way of fitting yourself unless these measurements were simply coincidental as a result of your fit.
    I guess you could look at it that way and make it sound all technical and mysterious, but quite simply fitting systems (like Retul etc.) record this, among other limb angles and ranges of motion, and adjust the fit to get nominal angles and ranges of angles based on what has been observed to work for the majority of riders. So, the knee angle is a key element of what they set. If not that, then what?
    ... 'cuz that's how I roll.

  11. #11
    wim
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    Quote Originally Posted by looigi View Post
    So, the knee angle is a key element of what they set. If not that, then what?
    Hogg uses an "acceleration in the extension of the knee," the observation of which indicates that the saddle is too high. This fits with Hogg's notion to throw out all numbers based on statistics and adjust everything on the base of an expert observation of the one rider being fitted. Having my doubts about the whole fitting business in general, I'm not even venturing a guess as which system gives the best results for the money and time spent.
    Last edited by wim; 01-26-2013 at 08:16 AM.

  12. #12
    FTR
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    Quote Originally Posted by looigi View Post
    I guess you could look at it that way and make it sound all technical and mysterious, but quite simply fitting systems (like Retul etc.) record this, among other limb angles and ranges of motion, and adjust the fit to get nominal angles and ranges of angles based on what has been observed to work for the majority of riders. So, the knee angle is a key element of what they set. If not that, then what?
    Sorry but I have been through Retul and BG and despite all of their angles and technology they both found me
    a) 2cm higher than I ride now using Hogg's method and more importantly
    b) injured (both)

    One of my BG fits was dismantled when I got home from the fit as it was completely unrideable.

    Tell me how you can have a recommended angle for every rider given that 2 riders who are of the same height, may have differing femur lengths, tibial lengths and foot lengths.

    Have you ever read Hogg's method? Your question is answered there.

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