Bike Frame Design – Steps and Issues in Designing a Women-Specific Alloy Road Bike Frame

by Sabinna on June 16, 2010

A few years ago, I set about designing an alloy road bike frame specifically for women.  Well, I was actually just designing a frame for myself, because the existing choices were very poor in Taiwan; these designs were formulated with the US and European markets in mind.

The market in Taiwan was (still is?) considered to be, practically, little different to anywhere else by the big players, and the not-so-big for that matter.  Smaller average physical dimensions of Taiwanese compared to Europeans, for example, was not a consideration for an export oriented manufacturing mindset. And, of course, women’s stature is, on average, smaller than men’s.

Therefore unless you were a woman with a stature considerably above average, you were not going to find a suitable frame.  This has limited the choices for women to be able to fully exploit the “surface” by taking part in road cycling and its efficiencies.

Steps to the GP1

The first issue was frame size. The optimum size for me is 43cm. At that time the smallest frames available were 49-50cm. In relation to frame geometry, I also wanted a more aggressive, dynamic design than was available. TT bikes had captured many cyclists imaginations, and so were always in the back of my mind as I was developing this optimum design.

What I was trying to achieve was a more performance-oriented design without sacrificing too much comfort in a range of small sizes–41cm and 43cm–that would open up a new set of cycling experiences for Taiwanese women, or women having similar physiques elsewhere.

The head tube was the immediate focus. Longer will be more comfortable and stable, most other frames being around 12cm.  I decided  for a shorter 10cm, bringing it closer to a full-on racing geometry. However, for practicality, I ended up going with a 10.5cm head tube for the first production, with a 52cm top tube. I decided on a seat tube angle of 75 degrees due to the small frame size (TT influence here also)–the larger sized frames would have angles of 73 or 74 degrees.

One key variable that could not be changed in all this was the stem. The minimum length available to me was 9cm. Another variable that could be only altered slightly was the stack height. Higher is more comfortable (counterbalancing a TT oriented geometry), but too many spacers really dilutes the aggressive look of the whole thing.

I settled on this geometry for the first production. After a few weeks of riding I felt the top tube was too long, so decreased it to 51cm and increased the head tube to 11cm in the next production. I also opted to increase the RC from 401mm to 405 mm giving a more relaxed riding position–striving hard to find a balance between performance and comfort.

It was still not quite right. With the head tube length unchanged, I reduced the top tube to 50.5. This combination worked well. It was a comfortable ride, but also had that dynamic edge that I was looking for. In sum, this was the final geometry for the small sizes that I was after: the third production produced the goods.

Additional measures I took to make the whole assemblage as suited to female anatomy as I could included a preference for SRAM Rival groupset. The attraction here was the reach of the levers was not as great as Shimano for example. The shifting was as good, if not better (although I have some reservations about SRAM now that I will comment on when time permits). I also sourced handlebars with a shallower drop than was generally available. For me the whole package worked really quite well.

GP2 an advance on GP1

With my “GP2″ I upgraded the seat stays to carbon and developed cooler decals. GP1 was a bit too much toward the “hello kitty” style of design that I was actually aiming to get away from.

The thing to note about all of this is that it was all very personal. These frames are the result of using what I knew already to explore areas that I did not know much about. All of it was driven by my feelings about what was right. As it turns out the feedback from cyclists has been good. This basic geometry has gone on to influence other unisex designs, one of which turned into a best-seller.

I have been surprised that the GP2 did not do better than GP1–both have done around the same in terms of overall sales. I guess there’s a lesson there in that “cool” is most certainly relative. But delivering a “cool” product comes about from the pursuit of the personal whilst being attentive to market feedback.

Women vs Men-which differences really make the difference?

Finally, I was operating under the assumption that, on average, women are shorter than men. This was based on a widely held assumption, unquestioned by myself, that women’s physiques are significantly different than men’s.

Gale Bernhardt in The Female Cyclist, suggests, based on anthropometric data gathered by NASA from a mixed population of military men and women, that this is not necessarily so (there’s also some interesting commentary on the cost effectiveness of producing for a marginal sector of the market).

“Physique” needs to be broken down into specific variables: Femur length; Tibia length;  Leg length; Torso length; Hand to shoulder length; Hand length. The average NASA values for these are given for both genders.

Let’s take leg length as the point of comparison. For a man and a woman of equal leg length, their torso lengths only differ by one-tenth of an inch. The main concerns for a woman would be smaller hand length and stem length. The issues faced are reach to the brake levers “the distance from the center of the transverse tube of the handlebars to the brakes, and brake-lever set up.”

Yes there are average differences between men and women. But it would seem that the important differences in relation to bike fit need to be approached from a more discriminating perspective than that of whether or not a cyclist is simply male or female.

Evidence of this on my own part is that my unisex designs have been enthusiastically embraced by many women who have not been attracted by the GP series. The important thing is to get good advice at the shop and/or a professional fit, on an individual basis.

My advice to any female cyclists in the market for a bike is to carefully evaluate any marketing talk centering on a bike’s greater suitability for them because the bike has been specifically engineered to better fit a woman’s body.

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