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  1. #1
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    Bike Fit using inseam: just go by jean size?

    as the title says.

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    Your "bike inseam" isn't the same as your pant inseam length. To meeasure your bike inseam, stand with your back to a wall in your stocking feet with your feet about 10" apart. Shove a moderately thick book with the spine on top up between your legs and press it up firmly (not hard, you're not trying to hurt yourself) until it stops and against the wall simultaneously. Mark the top edge of the book on the wall (having a helper is a real plus). The distance from that mark to the floor is your bike inseam.

    For example, I'm 5'9" and wear a pants inseam of 30" but my bike inseam measures 83.5 cm or 32.8". Use the bike inseam to help establish your initial saddle height and there are several formulas to get the first try. Refine it from there based on your personal comfort level.

    As to choosing frame size, "standover height" is only a beginning. You don't want a frame so big you can't safely stand over the top tube but that's not the only important measurement. Top tube length is also a critical distance as it controls your reach to the bars.

  3. #3
    headtube. zzyzx_xyzzy's Avatar
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    Quote Originally Posted by adlai View Post
    as the title says.
    nope. pants inseam varies depending how they sit on different people's waist/hips, how much crotch clearance they're made with(*), how much sock you like showing, etc. For standover on a bike you really want to know how long the leg bones are, ground to pubic bone.

    i wear a pants inseam of 36" but the bike inseam is more like 39".

    (*) which may contribute to the perception that "women have proportionately longer legs than men" which isn't true if you're measuring actual legs.

  4. #4
    DOS
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    Quote Originally Posted by zzyzx_xyzzy View Post
    (*) which may contribute to the perception that "women have proportionately longer legs than men" which isn't true if you're measuring actual legs.
    The "women have different proportions than men" argument has nothing to with inseam, but addresses leg to torso ratio and measures from waste. It has nothing to do with standover issues but reach. That is a 5'4" woman will generally have shorter torso and therefore shorter reach than a 5'4" man. This is why WSD bikes have shorter top tubes than similarly sized stadard design bikes.

    But yes, bike inseam is measured from floor to pubic bone.
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    headtube. zzyzx_xyzzy's Avatar
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    Quote Originally Posted by DOS View Post
    The "women have different proportions than men" argument has nothing to with inseam, but addresses leg to torso ratio and measures from waste. It has nothing to do with standover issues but reach. That is a 5'4" woman will generally have shorter torso and therefore shorter reach than a 5'4" man. This is why WSD bikes have shorter top tubes than similarly sized stadard design bikes.
    an off topic discussion of a throwaway comment, but...

    the background knowledge you need to understand what I was saying in the previous post is that the claim that women have shorter torso length and longer leg length compared to men of the same height... is a myth. It has repeatedly has been examined in or been a control component of biomechanics studies and found to be false. A few examples quickly pulled up in a search:

    Preece MA, Pan H, Ratcliffe SG. 1992 Auxological aspects of male and female puberty. Acta Paediatr. 383:1113
    Gallagher D, et al. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J Appl Physiol. 1997 Jul;83(1):229-39.
    E.S. Chumanov et al. Gender differences in walking and running on level and inclined surfaces. Clinical Biomechanics 23 (2008) 12601268

    SO, my original footnote was, one begins to wonder where the mythology of the long female leg came from, and pants inseam would be one candidate.

    As for "women specific" designs. if you compare equally tall "normal" and "WSD" frame geometry, e.g. I looked at the Trek 7.6 and comapred the "WSD", edition to the um, "non-gender-marked" edition. Matching frames with equal headtube lengths, I found that the top tubes on the WSD frames were shorter by less than a centimeter. But the seat tube in the WSD frames was also steeper by a full degree. The net result (as long as you understand what the impact of seat tube angle is) is NO DIFFERENCE. When you set the rider's proper saddle setback it will be further back in the clamp on the "WSD" frame. but the saddle to bar reach is actually the same. From most bike manufacturers, then, "women specific" geometry is another myth.

    Which is not to say that women under 5'4" or thereabouts don't tend to have problems with too long a reach, but it's the same reach problem that ALL shorter people face independently of gender. Georgina Terry has the right answer in using a smaller wheel in front, but she ought to be selling small-front-wheel bikes to short men as well.

  6. #6
    Extra Medium Member redtires's Avatar
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    The other aspect, and I'm not sure how you are planning on making sure your bike measurements are going to match what you want, but different manufacturers use different sizing methods. For example, for many production bikes, I like a 56 c-c frame both seat tube and top tube. However, the Fuji I ride is their "58"cm as it is measured from the center of the bottom bracket to literally the tipy top of the seatpost clamp. It does have a 57c-c top tube, however I have had zero problems simply using an 11cm stem vs. a 12cm. Technically speaking, with obvious caveats, the top tube length and seat tube angle are two of the most important aspects of proper frame fit.
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    Hi, I read somewhere,,can't remember that its inseam multplied my 1.09. I'm a 32. Which is 34 & 7/8. I just bought a new Masi, they call it a 60CM. Its got a 22" seat tube, top tube is ,,, 22" center to center. I got 180MM cranks. I love a high Bottom Bracket,tighter cornerings too.
    If you want my own personal bike fitting formula. Place your elbow on the nose of the saddle. Reach with your fingers toward the stem. Place a level on the saddle,center the rails a bit. I've learned that a saddle too far forward will give you lower back pain,on a drop bar bike anyways.Every bike catalog pics I've seen from the 1970's and 80"s the saddle is shown centered over the bottom bracket spindle and level. Cheers Chris

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    Senior Member Torchy McFlux's Avatar
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    Old fast and dirty bike shop sizing method: Straddle the toptube of the road bike with both your feet flat on the floor. If you've got about an inch of clearance between your crotch and the tube, it's your size.

  9. #9
    30 YR Wrench BikeWise1's Avatar
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    Quote Originally Posted by Torchy McFlux View Post
    Old fast and dirty bike shop sizing method: Straddle the toptube of the road bike with both your feet flat on the floor. If you've got about an inch of clearance between your crotch and the tube, it's your size.
    This is ONLY partially valid with level top tube bikes, which you hardly see anymore.

    The real critical measurement is top tube/stem combo. That is what determines weight distribution and to a large degree, comfort.

    If you are in a shop and someone has you stand over a top tube and proclaims "it fits" without getting at least a look at you ON the bike, run! You are dealing with idiots.

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    Quote Originally Posted by BikeWise1 View Post
    This is ONLY partially valid with level top tube bikes, which you hardly see anymore.

    The real critical measurement is top tube/stem combo. That is what determines weight distribution and to a large degree, comfort.

    If you are in a shop and someone has you stand over a top tube and proclaims "it fits" without getting at least a look at you ON the bike, run! You are dealing with idiots.
    It's not 'one or the other'. If you were to walk into a shop and someone told you that this bike fits based on the top tube measurement without checking to see if you can stand over the bike, you'd still be dealing with an idiot. Of the measurements on a bike, standover is second only to headtube length in terms of variability from brand to brand on a bike of a given size and given application.
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  11. #11
    30 YR Wrench BikeWise1's Avatar
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    Quote Originally Posted by cyccommute View Post
    It's not 'one or the other'. If you were to walk into a shop and someone told you that this bike fits based on the top tube measurement without checking to see if you can stand over the bike, you'd still be dealing with an idiot. Of the measurements on a bike, standover is second only to headtube length in terms of variability from brand to brand on a bike of a given size and given application.
    I never said it was "one or the other"! It just can't ONLY be inseam, and that of the two, more attention must be paid to cockpit and with it, stem length and angle. ;-)

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    Quote Originally Posted by BikeWise1 View Post
    I never said it was "one or the other"! It just can't ONLY be inseam, and that of the two, more attention must be paid to cockpit and with it, stem length and angle. ;-)
    That's particularly true with "compact" frames. You can have plenty of standover clearance on a frame that way too big based on top tube length.

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    Quote Originally Posted by zzyzx_xyzzy View Post
    an off topic discussion of a throwaway comment, but...the claim that women have shorter torso length and longer leg length compared to men of the same height... is a myth. It has repeatedly has been examined in or been a control component of biomechanics studies and found to be false. A few examples quickly pulled up in a search [snip]
    I read your second two examples (couldn't access the first) and didn't find them to be studies of relative proportions whatsoever. The Chumanov paper didn't seem to make any reference to this issue at all. Do you have a better source (i.e. one which discusses the issue directly), or perhaps you can direct me to a specific page or quotation from your sources? Thanks.

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    Quote Originally Posted by BikeWise1 View Post
    I never said it was "one or the other"! It just can't ONLY be inseam, and that of the two, more attention must be paid to cockpit and with it, stem length and angle. ;-)
    Sorry but when you use the words 'the real critical measurement is the top tube/stem combo' you are implying that standover is only secondary. The cockpit can be adjusted with saddle movement and stem length. Standover can't. It's highly dependent on the person as to which is more critical. And given that the top tube length is relatively standard while standover is more variable, the standover height needs to be address as well as the top tube length. Standover becomes much more important for small people than for average sized people as well.
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    headtube. zzyzx_xyzzy's Avatar
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    Quote Originally Posted by scruggle View Post
    I read your second two examples (couldn't access the first) and didn't find them to be studies of relative proportions whatsoever. The Chumanov paper didn't seem to make any reference to this issue at all. Do you have a better source (i.e. one which discusses the issue directly), or perhaps you can direct me to a specific page or quotation from your sources? Thanks.
    in both papers, just look at table 1.

    really, leg length is such low hanging fruit that it is not an interesting topic of study. it was covered decades ago, hence, the studies not available online. a more recent study specifically of relative proportions would not have been novel, hence not funded or published. this unfortunately allows myth propagation.

    more recent papers are reporting on more interesting (less well trodden) areas. They have to control for leg length, so they incidentally measure and report on it in the first table.

    ETA: if you want to play with some anthropometric data, try here.
    http://mreed.umtri.umich.edu/mreed/downloads.html

    Try the army data and see if you can come up with any combination of skeletal dimensions where the individual variance doesn't totally swamp any gender differences...
    Last edited by zzyzx_xyzzy; 07-20-10 at 06:11 PM. Reason: database

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    Quote Originally Posted by BikeWise1 View Post
    This is ONLY partially valid with level top tube bikes, which you hardly see anymore.

    The real critical measurement is top tube/stem combo. That is what determines weight distribution and to a large degree, comfort.

    If you are in a shop and someone has you stand over a top tube and proclaims "it fits" without getting at least a look at you ON the bike, run! You are dealing with idiots.
    Yes well, please note my use of the words "old", "fast", "dirty", and "road bike". They were used for a reason.

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    Can't get to any bike shop to test ride any conventional diamond frame bicycle to at leas have a little idea of size?


    If so, Why? Remote Location?

    Most shops I've ever worked in have people who work there who want people to enjoy riding a bike .. properly sized,
    even if they don't sell it on the spot.

  18. #18
    DOS
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    Quote Originally Posted by zzyzx_xyzzy View Post
    an off topic discussion of a throwaway comment, but...

    the background knowledge you need to understand what I was saying in the previous post is that the claim that women have shorter torso length and longer leg length compared to men of the same height... is a myth. It has repeatedly has been examined in or been a control component of biomechanics studies and found to be false. A few examples quickly pulled up in a search:

    Preece MA, Pan H, Ratcliffe SG. 1992 Auxological aspects of male and female puberty. Acta Paediatr. 383:11–13
    Gallagher D, et al. Appendicular skeletal muscle mass: effects of age, gender, and ethnicity. J Appl Physiol. 1997 Jul;83(1):229-39.
    E.S. Chumanov et al. Gender differences in walking and running on level and inclined surfaces. Clinical Biomechanics 23 (2008) 1260–1268

    SO, my original footnote was, one begins to wonder where the mythology of the long female leg came from, and pants inseam would be one candidate.

    As for "women specific" designs. if you compare equally tall "normal" and "WSD" frame geometry, e.g. I looked at the Trek 7.6 and comapred the "WSD", edition to the um, "non-gender-marked" edition. Matching frames with equal headtube lengths, I found that the top tubes on the WSD frames were shorter by less than a centimeter. But the seat tube in the WSD frames was also steeper by a full degree. The net result (as long as you understand what the impact of seat tube angle is) is NO DIFFERENCE. When you set the rider's proper saddle setback it will be further back in the clamp on the "WSD" frame. but the saddle to bar reach is actually the same. From most bike manufacturers, then, "women specific" geometry is another myth.

    Which is not to say that women under 5'4" or thereabouts don't tend to have problems with too long a reach, but it's the same reach problem that ALL shorter people face independently of gender. Georgina Terry has the right answer in using a smaller wheel in front, but she ought to be selling small-front-wheel bikes to short men as well.
    Didn't mean to imply that I thought the theory was correct. No idea one way or the other. Just that it had nothing to do with inseam.
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