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  1. #1
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    A new (I think) rule of thumb regarding bike fit

    Hi,

    My clothing inside leg is 28"/29", I prefer the latter, but an unusual
    size, and 28" fits better than 30", depending on acceptable crumple.

    I measured both my bike today, centre of the crank along the tubes
    to the top of the saddles, the road bike is 29", the folder 28.5".

    Seat height is set so my legs will lock out using my instep over
    the pedal. i.e.very near as high as it will go, with no consideration
    of being able to touch the ground sat in the saddle for the height.

    rgds, sreten.

  2. #2
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    What you have discovered is what works for you. I replaced your numbers with mine, and they are considerably OFF.

  3. #3
    Senior Member rebel1916's Avatar
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    Why on earth would you ever think, that what seems to work for one person, could be generalized to a new rule of thumb?

  4. #4
    Senior Member Loose Chain's Avatar
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    I do not think pants size is a good measure for bike fit. There are general rules of fit that provide a close starting point but in an age of saggy pants and weird fitting cloths, I doubt your clothing inseam is a good rule of thumb for anybody but for yourself.

    LC
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    I was once told that only _ussies needed lower than 42/21 gearing.

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  5. #5
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    Quote Originally Posted by rebel1916 View Post
    Why on earth would you ever think, that what seems to work
    for one person, could be generalized to a new rule of thumb?
    Hi,

    Because I consider myself pretty averagely proportioned.
    It clearly won't work with a different way of setting seat height.

    rgds, sreten.

  6. #6
    Senior Member rebel1916's Avatar
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    Almost by definition, one man's experience can not be a rule of thumb. Homework assignment - Grab 22 of you closest friends, check your system out on them, and report back.

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    Hi,

    I haven't a hope in hell of getting the people I know
    who ride bikes to set their seat heights correctly.

    rgds, sreten.

  8. #8
    Senior Member Loose Chain's Avatar
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    Quote Originally Posted by rebel1916 View Post
    Almost by definition, one man's experience can not be a rule of thumb. Homework assignment - Grab 22 of you closest friends, check your system out on them, and report back.
    But, as a human engine, seated on a bicycle, there actually has been proven repeatedly optimal configurations for seat height and posture on a bicycle. These "rule of thumb" guides are not perfect but they get most people into the zone where only minor adjustments are needed to account for differing peddling styles, comfort or other practical factors, but PANTS inseam length figures into none of them.
    Steel is Real

    I was once told that only _ussies needed lower than 42/21 gearing.

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  9. #9
    Senior Member rebel1916's Avatar
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    Quote Originally Posted by Loose Chain View Post
    But, as a human engine, seated on a bicycle, there actually has been proven repeatedly optimal configurations for seat height and posture on a bicycle. These "rule of thumb" guides are not perfect but they get most people into the zone where only minor adjustments are needed to account for differing peddling styles, comfort or other practical factors, but PANTS inseam length figures into none of them.
    Holy shnikes, clean out your listening ears. I didn't say rules of thumb don't exist, I said that they could not be extrapolated from the single experience of one man. Even if he has been riding for almost 6 months now.

  10. #10
    coprolite fietsbob's Avatar
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    Seems when reach and stem is right, I get a line of sight straight through the steering axis, looking down.

  11. #11
    Not About Hardware Bandera's Avatar
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    Oddly enough the topic of the proper fit on a bicycle has been given more than cursory thought since the Safety Bicycle was invented, often by folk who make a living riding one.

    Here's a tome w/ some musings on fit by a World/Multi-TDF champ that might be worth a glance: "Greg Lemond's Complete Book of Bicycling".
    You just might want to peruse it and meditate on the attached pic.

    -Bandera
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  12. #12
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    Hi,

    Whilst I would not mind what I suggested being shot to pieces by someone
    who knows what they are talking about, I do mind the clueless pointlessly
    pontificating about basically nothing, experts on deriding stuff they don't
    understand, thinking that somehow makes them appear to be clever.

    What I said is clear and simple, but I'm obviously wasting my time.

    rgds, sreten.

  13. #13
    Senior Member rebel1916's Avatar
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    Yeah, that's it. Everyone is crazy but you.

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    Sreten: An interesting observation, but one that does not, sadly, work in general. There is, FWIW, a rule of thumb for saddle height. It is inseam x .883. The inseam, BTW, needs to be accurately measured. Pants inseam is not good enough.

    As for the rest, bike fit is an area populated largely by opinionated A-holes who know just enough to have passionately held beliefs but not enough to really know why they're defending them. IOW, welcome to BF.

  15. #15
    Senior Member rebel1916's Avatar
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    Quote Originally Posted by Six jours View Post
    As for the rest, bike fit is an area populated largely by opinionated A-holes who know just enough to have passionately held beliefs but not enough to really know why they're defending them. IOW, welcome to BF.
    You realize you are describing the OP right there, right?

  16. #16
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    Y'all are welcome to take it however you like. I myself am, of course, posting here too...

  17. #17
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    Hi,

    Some of you are very a sad pointlessly offensive bunch.

    Do any of you really think I was taking myself seriously ?

    Your attitude problem, not mine.

    rgds, sreten.

  18. #18
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    Quote Originally Posted by rebel1916 View Post
    You realize you are describing the OP right there, right?
    Yeah, if your proud of that post your the definition of a hypocrite, rgds, sreten.

  19. #19
    Long Distance Cyclist Machka's Avatar
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    Bicycling Medicine by Arnie Baker

    To quote Bicycling Medicine by Arnie Baker

    "Seat height is a compromise between aerobic economy, aerodynamics, bicycle handling, injury prevention, muscle fatigue, stroke fluidity, and power.

    ...

    ... Base the seat height on the angle from the horizontal formed by the knee at the bottom of the pedal stroke. This angle is measured in degrees of flexion. With the lower leg extended straight out, this angle is zero degrees by convention. As a starting point, many racers are best positioned so that the angle of the knee is 25 degrees. This is a good compromise between aerobic economy, muscle fatigue, stroke fluidity, and power.

    ...

    Aerobic economy and power can be improved with a higher position: a knee angle of 15 to 20 degrees.

    ...

    More control can be obtained with a lower position: a knee angle of 30 degrees. This is important, for example, when riding a bicycle on a steep velodrome.

    Riders with pain in the anterior (front) knee - due, for example, to arthritis or patellar tendonitis - do better with a higher seat position and a knee angle of 15 to 20 degrees. Riders with pain in the posterior (back) knee, in the Achilles tendon, or in the back of the calf or thigh do better with a lower seat position and knee angle of 25 to 35 degrees."
    (pages 119 - 120)


    "A seat height that results in 25 to 30 degrees of knee flexion when the pedal is at the bottom of the stroke tends to result in the least injury but is not optimal for cycling power or aerobic efficiency.

    The higher your seat, the more likely you are to have pain in the back of your knee, Achilles tendon pain, or buttock ache. Those with limited flexibility are the most likely to have problems."
    (page 148)



    I highly recommend reading Bicycling Medicine by Arnie Baker



    Personally, I need the slightly lower saddle height described above, and I can find the correct saddle height by doing the following ...

    -- getting on my bicycle and riding on flat ground for a few minutes to warm up and get comfortable on the bicycle

    -- coasting, placing my heel on the pedal and dropping the pedal to the 6:00 position

    -- and if my leg has just a very slight bend in it, that's about right.

  20. #20
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by sreten View Post
    Hi,

    My clothing inside leg is 28"/29", I prefer the latter, but an unusual
    size, and 28" fits better than 30", depending on acceptable crumple.

    I measured both my bike today, centre of the crank along the tubes
    to the top of the saddles, the road bike is 29", the folder 28.5".

    Seat height is set so my legs will lock out using my instep over
    the pedal. i.e.very near as high as it will go, with no consideration
    of being able to touch the ground sat in the saddle for the height.

    rgds, sreten.
    Congratulations on finding something that works for you. It's really hard to correlate it with the other rules of thumb (ROTs) that are often used. First reason, is that most quantitative ROTs are based on a precise measurement of cycling inseam, sometimes called pubic bone height (PBH). It's a relatively fixed measurement since it depends on the position of a particular location on your skeleton and a hard flat floor you would be standing on, and it's measured to the best available precision with commensurate accuracy. Measuring your trouser inside leg is quite variable due to differences in the rise of trousers, other aspects of how they are cut, and of course cuff tailoring based on desired cuff crumple. Plus it's common to measure trousers to the half or quarter of an inch (cm to half-cm in EU and UK?), and this is really not feasible with fabrics since they stretch even to a small degree.

    As far as your knee lock technique, that sounds like a fine way to get a starting point. Usually I find it to be only a starting point, and tend to gradually raise it based on stress sensations in the front and side of my knee. But I won't go higher than the location where pelvic rocking and resulting chafing sets in.

    This is my personal ROT based on the old traditional "heel on pedal with straight leg" approach. Possible differences with yours:

    Heel on pedal versus instep on pedal
    Knee "locked" straight versus leg straight and both legs simultaneously hanging relaxed

    Similar to the traditional but hard to see the exact correlation.

  21. #21
    Senior Member Road Fan's Avatar
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    Quote Originally Posted by Machka View Post
    To quote Bicycling Medicine by Arnie Baker

    "Seat height is a compromise between aerobic economy, aerodynamics, bicycle handling, injury prevention, muscle fatigue, stroke fluidity, and power.

    ...

    ... Base the seat height on the angle from the horizontal formed by the knee at the bottom of the pedal stroke. This angle is measured in degrees of flexion. With the lower leg extended straight out, this angle is zero degrees by convention. As a starting point, many racers are best positioned so that the angle of the knee is 25 degrees. This is a good compromise between aerobic economy, muscle fatigue, stroke fluidity, and power.

    ...

    Aerobic economy and power can be improved with a higher position: a knee angle of 15 to 20 degrees.

    ...

    More control can be obtained with a lower position: a knee angle of 30 degrees. This is important, for example, when riding a bicycle on a steep velodrome.

    Riders with pain in the anterior (front) knee - due, for example, to arthritis or patellar tendonitis - do better with a higher seat position and a knee angle of 15 to 20 degrees. Riders with pain in the posterior (back) knee, in the Achilles tendon, or in the back of the calf or thigh do better with a lower seat position and knee angle of 25 to 35 degrees."
    (pages 119 - 120)


    "A seat height that results in 25 to 30 degrees of knee flexion when the pedal is at the bottom of the stroke tends to result in the least injury but is not optimal for cycling power or aerobic efficiency.

    The higher your seat, the more likely you are to have pain in the back of your knee, Achilles tendon pain, or buttock ache. Those with limited flexibility are the most likely to have problems."
    (page 148)



    I highly recommend reading Bicycling Medicine by Arnie Baker



    Personally, I need the slightly lower saddle height described above, and I can find the correct saddle height by doing the following ...

    -- getting on my bicycle and riding on flat ground for a few minutes to warm up and get comfortable on the bicycle

    -- coasting, placing my heel on the pedal and dropping the pedal to the 6:00 position

    -- and if my leg has just a very slight bend in it, that's about right.
    Machka, in your own technique, do you turn the pedal upside down? Seems to me the design of the pedal and the shoe are significant variables. I usually ride with toe clips or clip-free rattraps. I use the rattraps to set height, and fine tune when I switch over to my touring toeclip pedals.

    I share your respect for Baker's writings and procedures, but it's a challenge to measure those angles consistently, or without a similarly dedicated partner. I had a fitting done on that basis (i.e. using a goniometer and based on knee angle) and it worked out quite well for a few years at least. Sadly the gent went out of business ...

  22. #22
    Long Distance Cyclist Machka's Avatar
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    Quote Originally Posted by Road Fan View Post
    Machka, in your own technique, do you turn the pedal upside down? Seems to me the design of the pedal and the shoe are significant variables. I usually ride with toe clips or clip-free rattraps. I use the rattraps to set height, and fine tune when I switch over to my touring toeclip pedals.

    I share your respect for Baker's writings and procedures, but it's a challenge to measure those angles consistently, or without a similarly dedicated partner. I had a fitting done on that basis (i.e. using a goniometer and based on knee angle) and it worked out quite well for a few years at least. Sadly the gent went out of business ...
    I use the Shimano Multi pedal - platform on one side, clip on the other. So when I use my heel on the pedal, and slight bend in the knee, technique, it's with my heel on the platform side of the pedal.

    And yes, there may be a little bit of fine tuning required. That is a starting point. From there I might go up or down by millimetres depending on a wide range of factors.

    That's the technique I've been using for years, but in 2010, Rowan and I were fit on the tandem we bought, and it turns out that the saddle height we were measured to, using angles etc., is the same saddle height I would have set it to using the heel on pedal, slight bend in knee, method.

  23. #23
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    Problem with the OP's proposal is that no-one agrees on what an appropriate pants inseam is. One person likes floods, another likes a deep break at the instep. OP says his pants inseam could be from 28" to 30", that is a 2" range which is large enough to make the rule not workable.
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  24. #24
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    Quote Originally Posted by Bandera View Post
    Oddly enough the topic of the proper fit on a bicycle has been given more than cursory thought since the Safety Bicycle was invented, often by folk who make a living riding one.

    Here's a tome w/ some musings on fit by a World/Multi-TDF champ that might be worth a glance: "Greg Lemond's Complete Book of Bicycling".
    You just might want to peruse it and meditate on the attached pic.

    -Bandera
    An old book, but it gave me lots of good guidance 20 years ago. I used his seat height formula and found I needed to raise my saddle, even though I thought I had the right "bend" in the knee. Worked well.

  25. #25
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    Quote Originally Posted by Road Fan View Post
    As far as your knee lock technique, that sounds like a fine way to get a starting point.
    Usually I find it to be only a starting point, and tend to gradually raise it based on
    stress sensations in the front and side of my knee. But I won't go higher than the
    location where pelvic rocking and resulting chafing sets in.
    Hi,

    The general rule is to use heel lockout, but if you go to instep lockout
    that is not a starting point at all, it is very near the highest you can go.

    If you can lockout with the ball of the foot over the pedal then
    you are talking inevitable pelvic rocking to avoid full leg locking.

    To me it is not complicated regarding standing on one pedal :

    Ball of foot you can lift yourself off the saddle.
    Instep it should be ~ 50/50, not on or off.
    Heel you cannot lift off the saddle.

    The above is good enough for me.

    rgds, sreten.
    Last edited by sreten; 07-08-13 at 06:07 PM.

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