# torso/leg length ratio: how to measure



## pdxtim (Nov 15, 2004)

I'm a physical therapist who does some bike fitting, and several times while reading articles on bike fit, frame geometry, etc. I've come across statements regarding individuals who have "long trunks and short legs", and conversely "short trunks and long legs". The author will usually then state that those who have long trunks do better with bikes with long top tubes, etc. Makes sense to me. I have not been able, though, to ascertain exactly what constitutes a "long leg/short trunk" individual or vice versa. What is the typical ratio? What anatomical landmarks and measurements are used? I've been searching for the answer to this for months. Does anyone have knowledge in this area or know of a pertinent website?

I'll donate one of my bikes to whoever has the answer................well, maybe my son's bike (kidding).


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## Wookiebiker (Sep 5, 2005)

I doubt there is a specific ratio that would denote one or the other. However myself for example am 6 feet tall with a 31.5" inseam. That would constitute a long body and short legs. I could never get a good fit on an off the shelf bike because I had to move so far forward on the bike.

With short legs, not only do you need a long top tube but if the femur is short you need steep seat tube angles otherwise your knee ends up too far behind the KOP position. Generally on bigger bikes they have laid back STA's so my bikes looked rather funny when set up for me.

When I went custom, I was finally able to get fit correctly on the bike. My bike numbers are these:

58.1cm top tube length
74.5 degree seat tube angle
49.7cm seat tube length
14,5 cm head tube length
73.5 degree head tube angle

It has made all the difference in the world having a bike that actually fits in how it rides, handles, comfort and overall power output.

I would guess that most people fit into a "Bell Curve" when it comes to leg length/torso ratio. You need to find out what the norm is, then when somebody falls outside of it you know a custom frame is likely needed.

BTW...My wife is on the opposite end of the spectrum. She is 4'11" tall and has a 28.5" inseam length with long femurs. Most small womens bikes come with 75 degree + STA's and she needs something more in the 72.5 - 73 degree range.


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## wim (Feb 28, 2005)

*Hinault/Genzling book. Long post.*

The now out-of-print book “Road Racing Techniques and Training” by Bernard Hinault and Claude Genzling (ISBN 0-941950-13-1) addresses this ratio in the chapter “Morphology, Position and Frame Design.” The authors first define seven body measurements:

1. Height – no shoes.

2. Inseam E – 1.5 cm wide carpenter’s square raised as much as possible into the crotch, no shoes.

3. Thigh C – rider on stool, back and pelvis against the wall. Lower legs vertical. Put straightedge against two kneecaps, measure the distance from straightedge to the wall.

4. Lower leg J – same position as thigh measurement, no shoes. Put straightedge on top of the knees in front of the beginning of the thigh muscles. Measure from straightedge to ground.

5. Trunk T – rider on level stool, pelvis and back against the wall, shoulders horizontal. Place carpenter’s square on the bulge of the collarbone, measure distance mark on the wall at this height and the top of the stool.

6. Arm B – previous position. Rider grasps a small cylinder the same diameter than his handlebars. Without moving shoulders forward and back against he wall, rider moves his straight arm to a horizontal position. Measure from wall to edge of cylinder.

7. Forearm A – arm at 45 degrees, rider bends elbow to form a right angle between his upper arm and forearm. Measure the distance between the elbow and the cylinder.

The authors then address morphological differences, using the letters and definitions above. They state the norm of the ratio of thigh C to lower leg J as 1.11 in men, 1.14 in women. They claim that a larger C/J ratio has been observed in cycling champions: Coppi at 1.18; Merckx at 1.16; Hinault at 1.20.

Hinault and Ginzling then list a norms for trunk, arm and inseam ratios for men

T/E = 0.76 
B/E = 0.87 
A/E = 0.40

and explain briefly how these ratios (or variations thereof) can be used to figure a rider’s reach.

The authors don’t use the ratio of inseam to height because, in their words, “the size of the head and the neck, which have nothing to do with position, falsify the results."

Of course, the book is old, the translation from the French leaves much to be desired, and the norms are based on Western Europeans. It’s pretty much been relegated to the scrap heap of training literature, but I think it’s still a viable text. Somewhere in the beginning of the book, the authors say “the numbers propose, the rider disposes.” How true—at least for those riders who can hear what their body is telling them.


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## C-40 (Feb 4, 2004)

*rough guideline...*

If the person doesn't have an unusually long neck, then a height to inseam measurement tells quite a bit. Inseam is measured in bare feet to saddle-like crotch contact in bare feet. I've definitely got long legs for my short height. I'm 168cm tall with an 83cm inseam. That's a ratio of 2.024 or .494 depending on which way you want to express it. Tall riders are sometimes even more extreme. I've read many posts from riders who are 3-5 inches taller with no more leg length.

As for the appropriate TT length, arm length would be a significant factor. A long legged might have arms to match his legs (long) or to match his torso (short). Upper leg length is also a factor, if the rider adjusts the saddle to place his knee joint directly over the center of the pedal spindle. There's a lot of debate whether the saddle fore/aft position really affects pedaling torque or cadence. I tend to find that a further back saddle allows me to apply a bit more torque, but may impede my highest cadence. It definitely affect your comfort in the saddle and affects the bike's weight balance and handling. A saddle that's too far forward may leave the rider unbalanced over the saddle, with too much weight on his hands. 

Another thing to consider is that stock frames really don't vary all that much is reach. Reach is the horizontal distance from a vertical line through the BB to the head tube/top tube intersection point. It's affected by the seat tube angle. Comparing only the TT lengths of frames is not the correct way to compare the fit of a frame. A frame with a 54cm TT and 72.5 degree STA will fit about the same as one with a 52.5cm TT and 74.5 STA, once the saddle is in the same location relative to the BB. If you properly calculate the reach of a frames of the same size, most fall into a very narrow range with no more than 1cm deviation. With some brands now offering very few sizes, that range might be as large as 2cm.


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## Mark McM (Jun 18, 2005)

*All generalities are false*



pdxtim said:


> I'm a physical therapist who does some bike fitting, and several times while reading articles on bike fit, frame geometry, etc. I've come across statements regarding individuals who have "long trunks and short legs", and conversely "short trunks and long legs". The author will usually then state that those who have long trunks do better with bikes with long top tubes, etc.


Just like most rules of thumb, this one might only work as a starting point, or only work for otherwise "normal" people. But everyone is unique, and there are lot of other variables that leg/trunk length ratio doesn't account for in selecting frame geometry. For example, those with poor back flexibility, or simply prefer a more upright position, will probably want a shorter top tube, even if the they have long legs for their trunk length.

I myself am kind of at the opposite end. My proportions aren't too dissimilar to C-40's - I'm 169 cm tall with 82.5cm legs. Furthermore, I've got relatively long femurs relative to my shin length, which results in my saddle being pushed further back than "normal" to achieve a KOPs position. Both of these would suggest that I would need a frame with a shorter top tube to achieve the best "reach" dimension - and yet, I actually fit best on a frame with a longer top tube. This is probably due to a combination of a flexible back (I ride in a more bent over position than most) and long arms.


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## son_o_lars (Apr 27, 2007)

*frames with longer top tubes?*

I too am in the "long torso" camp. any suggestions on frames/brands better suited to this build?


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## wim (Feb 28, 2005)

> _I too am in the "long torso" camp. any suggestions on frames/brands better suited to this build?_


Same here. I've found Trek's Madone to be very long for their vertical size. Because of the odd way Madones are sized, put away any preconceived notions about your frame size when trying a Madone for size. The Madone that fit me best was stickered as a 58 cm, but its center-to-center size was a measured 54.5 cm.


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## son_o_lars (Apr 27, 2007)

*what about other treks. any other brands?*

Thanks for the reply RE Madones. Unfortunately, they are out of my price range. I am currently on a 56cm ("large") steel specialized Allez comp, and don't like the compact geometry. it is also too short (56.5 top tube, effective). Any suggestions for a 56/57ish frame with a longer top tube. I'm looking for an overall reach of about 70.5 cm according to measurements.


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## The Flash (May 6, 2002)

son_o_lars said:


> I too am in the "long torso" camp. any suggestions on frames/brands better suited to this build?


IME, the Giants have fit me really good. I ride a Scott CR1 Pro and have not problems, either....

The Flash


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## wim (Feb 28, 2005)

> _what about other treks. any other brands? _


I've no personal experience with other Treks, but all their road bikes are sized like the Madone—nominal size is the dimension from the center of the bottom bracket to the very top of the seat tube extension. 

I'm a "good enough" kind of guy when it comes to fit, and others here are much better than I am at crunching the numbers. I do know that you can only interpret top tube lengths together with seat tube angles. What a longer top tube gives you in increased reach, a shallower seat tube angle will take away.


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## Wookiebiker (Sep 5, 2005)

son_o_lars said:


> I too am in the "long torso" camp. any suggestions on frames/brands better suited to this build?


Lemond frames generally have long TT's, but laid back STA's so you will need a longer femur to compensate for the laid back STA. Generally worth a look though.


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