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Monday, October 1, 2012

More "women's specific" mythologizing

So it seems the women's specific myth isn't going away any time soon, unfortunately.  It doesn't seem to be discriminating between road or mountain bikes either, as a few more femme bikes have been released for the dirt.

I certainly have nothing against bikes made specifically for women....certainly my years spent fitting bikes and building custom rides has made me acutely aware that a bespoke bike (and all it's parts) makes for the most enjoyable ride possible.  I can appreciate wanting a bike a certain color -- not every woman is going to want the black or red or black/red bikes that predominate the industry.

Much of the bike market's marketing for women's specific bikes talks of ladies' special body measurements that require a bike made differently from a man's.  I have seen the different manufacturers reference frequently, and contradictorily, that women have:

  •  longer torsos relative to their height, 
  •  sometimes shorter torsos as well ;-)
  •  shorter arm reach
  •  longer reach relative to their torso length (??)
  •  longer inseam 
  •  surprise!  shorter inseam as well!
Confused yet?  Me too.

Let's look at some facts:

There have been thousands of studies going back hundreds of years, in the field of anthropometrics ( the science dealing with measurement of the size, weight, and proportions of the human body).  Many of the studies will have an "N" value (meaning how many participants were studied -- generally more is better) in the thousands or tens of thousands.  We have really good data on this, and you could (and people do) write thousands of pages on all the comparisons.  

I pulled some data from a University of Rhode Island study back in 2009 that was updated just in the spring of 2012.  To keep it simple, we'll just look at the data from one main table that measures:  Stature (overall height), eye height, mid-shoulder height, waist height, sitting height, buttocks height, eye height (sitting), upper arm length, lower arm + hand length, upper leg length, and lower leg length.  They're broken down into male and female groups with percentiles from the 5th to the 95th -- 95th represents the tallest while the 5th percentile represents the shorties.

Keep in mind that when you're study includes thousands of test subjects you're going to find the best way to measure them so that it's simple, clinically applicable and simple/fast.  So these measurements weren't taken off X-rays, MRI or other super-accurate (and expensive method).  Rather these were taken with simple measuring rigs and tape measures and so the dimensions measured are different sometimes than you would expect....for example torso length is measured with the subject sitting on a flat surface, and the measurement is taken from the seat of the "chair" up to the top of their sternum, so it includes the pelvis and thorax.

Still, we can get a  good idea of what the data shows.

So without belaboring this too much this is what their findings say:

(As a percentage of their overall body height)

Torso length

5th% percentile
males -- 35.5%  - so their torso makes up roughly 35% of their total height
females -- 34.2% 

males -- 34.5%
females -- 35.3%

Buttocks height

males -- 46.2%
females -- 45.5%

males -- 49.1%
females -- 48.3%

Upper Arm length

males -- 33.8%
females -- 35.0%

males -- 35.3%
females -- 36.4%

This is by no means a comprehensive list of all the measurements they took -- they had many more.  I just grabbed a smattering of them as a representative sample.

So let's put some of this into perspective....when considering any of these measurements, while there are differences, I'm not seeing any earth-shattering differences that would make me think you could, in any sort of reliable or useful way, manipulate a stock bicycle's frame geometry to match a certain rider, male or female, even if everyone followed the averages expressed in this study, which of course almost no one will (more on this later)

As an example, for upper arm length we see one of the larger differences between the male and female measurements -- 1.2%.  This represents an actual difference of around half a centimeter, or about the thickness of two nickels.

Furthermore the differences are a mixed bag -- when a leg measurement favors on gender in the 5th percentile, that same measurement may be greater (again, slightly) for the other gender in the 95th percentile.....or vice versa.

I looked at the tallest and shortest of the gender, but the results were the same in the middle heights -- consistently close and inconsistently favoring one side then the other.

And as I mentioned before, these are averages and small deviations on any measurement are blended in but will be minimized.  A female may fall into the 50th percentile for height and leg length but have arm lengths that fall into the 65th percentile. 

I recently had a male client, with moderate flexibility, who stood about 6'4" tall (193 cm) with a 37.5" inseam.  I've had a few clients built like this and most of them really did better on a custom geometry bike because their relatively short torso and middling flexibility restricted their handlebar position.  What differed about this client was his arm reach.  He had arm lengths of a man many inches taller, which made it much easier for him to reach his handlebars even if they were in a longer or lower position than we normally see with someone with his torso length. 

Something to consider is that these deviations from the norm -- like his extended arm reach -- aren't uncommon.  Not when you consider that 66% of people fall outside of one-half standard deviation from the average (while 32% fall greater than one full standard deviation away).

So now......given these small variations in the "averages" and the vast potential for deviations from these averages, how useful do you think it would be to alter the geometry of bike in order to fit one sex or the other better?

Add to that all the natural variations we see outside of body segment lengths, like flexibility and strength, and you have a nearly impossible task.  I know this makes it seem like it would be impossible to create a stock bike that fits ANYONE, when in fact standard sizes tend to work out okay for many (but not most) riders out there.  Those riders that they work well for are fortunate to have been born into close proximity of the average measurements.  This fortunate phenomenon is less common if your overall height is on the high or low end of the charts -- bike designs for the very big and very little are still lacking.

So how well do stock bikes fit the masses? 

In my experience about 25% of the population fits them with little or no changes to the bike. 

A full 50% require changes to bike parts that I would consider "significant" in nature. 

What's "significant"? An example would be requiring a stem with a rise above 15 degrees.  Often riders require multiple changes -- bar reach and height accommodations AND cleat and saddle adaptations as well. A simpler definition would be any change that's likely to affect the overall balance or handling adversely.  Now,  a 20 degree rise stem wouldn't render a bike unrideable, but it will be a compromise....the bike won't steer or handle the way the geometry was designed for, and the rider's overall balance and weight distribution will be "off" which can lead to many small issues (for instance, not being able to settle comfortably on a saddle, incomplete engagement of some of the more powerful leg muscles, or more weight on one or more contact points).

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