Technical FAQ: Who’s studying women’s-specific design?

Dear Lennard,
Recently I attended a seminar led by a well-known bike manufacturer that I will not name. The speaker stated that after “drilling down into the data” there is no unique differences in the frame geometry requirements for women versus men. Typically, women are considered to have longer legs and shorter torsos; however, many men share the same proportions. He added many women share what is considered to be the norm for men, shorter legs, longer torsos.

The reason I’m intrigued by this is if the bike industry is going to seriously attract women into cycling, shouldn’t they, along with the rest of the industry (meaning bike shops) start treating women as intelligent consumers rather than just go about what is often the practice — to “shrink it and pink it?” I believe it would be far better to discuss frame geometry as it relates to that person’s requirements, male or female, along with the desired experience the person is seeking, fitness, etc. rather than to simply break it down by gender.

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Have any in-depth studies been done in regards to bicycle geometry, looking at differences in body proportions in women versus men?
—Peter McMahon

Dear Peter,
That’s a very good question. I’m writing this in the car, driving in sluggish traffic on the way back from witnessing the total solar eclipse in Glendo, Wyoming. After such a joyous, even spiritual, experience based on hard science, it makes sense to address this question of whether a woman’s ride experience can be enhanced based on hard scientific data.

In my anecdotal experience as a framebuilder, I have found that there is no stereotypical women’s body geometry. Over 35 years of designing and building custom frames, I have built many bikes for women with long legs and short torsos relative to their height (which is often what you hear in the bike industry that defines women’s body dimensions), but I have also built many bikes for women with short legs and long torsos relative to their height. Furthermore, I have built a lot of bikes for Japanese women, and every single one of them was 5’1” or less and had shorter legs and a longer torso than most men and other women of similar height I’ve built bikes for. This is enough for me to believe that it also had to do with geographic heritage, and hence knowing where your customers, or their ancestors, came from.

Based on my limited snapshot of women’s overall body measurements, I certainly do not have sufficient data to make a blanket statement about women’s body dimensions as related to bike fit. I’ve built a lot more bikes for men than women, and I also know I don’t have enough data to say something like, “men have short legs and long torsos,” or, “men have long arms and long legs,” etc.; it obviously would not hold true across the board or even close to it. Since we all know innumerable men and women with short legs and long torsos and well as ones with long legs and short torsos, and any number of other variations in body dimensions, I think we can all agree that it is a hard thing to draw a firm conclusion about how to fit most women on bikes, and that it is a certainty that there will never be a fit formula that works for all women (or men). There will always be outliers.

To come up with an answer to your question, I interviewed product managers from two companies who have strong women’s lines, namely Specialized and Giant, as well as got some email responses to your questions from Felt and Trek.

Jim Felt, founder of Felt Bicycles, said, “We actually were one of the first to enter the (women’s bike) market, but not necessarily because we sought that opportunity. My marketing girl at the time was an ex-pro road racer and for years kept telling us that women need a specific bike with a slight change of spec to cater to their needs. I do believe it is a big plus to offer women what they are really looking for. Unfortunately, many women’s bikes suffer from poor handling due to that shorter riding compartment that affects the geometry to make them pass the toe-overlap safety standard. The funny thing is that if you ask any Pro women out there, if given the choice between a women’s-specific or the same thing the men ride, they will always go with the same thing the men ride.”

Dean Gore, marketing director for Trek, says, “For frame geometry, we have the luxury of seeing the body dimensions from thousands of Bontrager Precision Fit sessions. This is great, representational data of all different sizes and gender of riders that helps steer our engineers and designers.”

Stephanie Kaplan started as women’s product manager at Specialized and is now part of the men’s product management team. Kaplan is short as well as a fast rider, so women’s-specific, or at least, very small, top-end bikes, were essential for her. She, along with other product managers at Specialized, endeavored to create bikes based on relative differences between men’s and women’s anthropometric measurements.

Since men’s bikes constitute a larger percentage of the bikes that Specialized sells, it is harder to allocate resources toward women’s-only bikes. That said, the company gave Kaplan’s team the directive to look into it, and if they discovered a legitimate need for women’s-specific bikes, it would come up with the funds to make them.

Kaplan’s team started with a book detailing results of a US Army study from the 1970s, a book she says has been the bible for development of ergonomic chairs, etc., because few — and perhaps no — organizations besides the military have a way to get that much physical-measurement data on so many people. A large new data resource became available a few years ago, when Specialized purchased the ReTul fitting system a few years ago. ReTul uses computer methods to capture measurements from each rider. By putting LEDs on body joints and digitizing their location in space with video motion capture downloaded into a computer, ReTul had spent many years capturing anthropometric data on thousands of its customers. According to Kaplan, “ReTul has incredible data analysts on staff,” and they had put this data on the cloud just before Specialized bought the company, making it easily accessible for analysis.

When she was going through the data looking for distinctions in limb lengths for women versus men, Kaplan admitted that, “I looked into it with my internal bias, trying to find that they (the need for different frames for men than women) were there.” Despite looking at the data with this bias, she and the other Specialized product managers working on the project found no correlation between gender and limb length. This data also showed no correlation between gender and a taller frame-stack dimension (Y-coordinate of the top of the head tube relative to the center of the bottom bracket). This was quite surprising to Kaplan and perhaps to many readers. Kaplan says, “What we were doing before (in bike designs for women) was right based on the information we had before. But [after discovering that their fit data doesn’t support different frame geometry for men and women] I’m not going to lie about it so we have a great marketing story.”

The data consisted of 4,000 fits from ReTul with full anthropometric data on each client. Additionally, the team looked at data from 36,000 Specialized Body Geometry (BG) fits from over a decade of fits all over the world, but this data consists of the bike fit only — the locations of the touch points of the bicycle in space. It also included gross body measurements like leg length, but not the detailed anthropometric data of the customers — for instance, the length from ankle to knee, knee to hip, etc. of each client—the way ReTul’s did. In addition to looking at detailed limb lengths from 4,000 individuals, the team analyzed, for instance, what handlebar width, saddle width, etc. clients of each gender with a given set of fit dimensions ended up with from 40,000 total bike fits.

Based on this data analysis, Specialized will be discontinuing frames with women’s-specific dimensions, like the Amira road-racing frame, and it is instead creating frame platforms with performance geometry specific to the category the rider self-identifies with, like endurance rider, hill climber, gravel rider, etc. For instance, the Tarmac frame now comes in 44-61cm, as small as the Amira, but it will be built into an entire line of women’s models; there will now be a Tarmac Men’s and a Tarmac Women’s bike. Women compare the Amira to the Tarmac Women’s, whereas men compare the SL5 Tarmac to the SL6 Tarmac. Kaplan notes that the bikes have changed a lot over the past year, and, interestingly, the men’s bikes even more than the women’s. Diverge men’s and women’s bike models launched this year as well.

This method of putting a rider’s usage ahead of their gender still accommodates gender-specific component selections, like saddle, handlebar, and crank length. Women will get the same frame as men, but all of the touch points would be dialed in for an average woman rider of that size. The data showed an average shoulder width for women of 40cm, and for men, 42cm. The average saddle width for women with the BG fitting system is 155mm, and it is 143mm for men. The crank length is 155mm on a women’s 44cm Tarmac and 165mm on the 49cm; whereas the men’s 49cm Tarmac has a 170mm crank. Many of these choices are based on data of what parts get switched out in a typical BG fit.

Even though the ReTul data indicated no correlation between gender and limb length, the total database of ReTul and BG fits indicated trends like, if a male rider has the exact same leg length as female, the woman would have her saddle 1cm lower. Kaplan says that, due to exposure of soft tissue, women tend to push back on the saddle and roll their hips back, thus creating a longer distance to the pedal for a given seat height. Her group didn’t feel the need to address this in the frame dimensions, but it clearly creates opportunities in saddle design.

Interestingly, Giant has also looked at lots of data and has come to different conclusions. Liv/Giant product manager Erin Lamb, being over 5’10”, comes at it from different personal needs than Kaplan. Lamb and Sophia Sheet, an engineer for Liv, started by looking at global anthropometric databases of men and women from all over the world as well as strength studies.

Some data Lamb and Sheet studied comes from government statistics from various countries around the globe, like the CDC Anthropometric Reference Data for Children and Adults: United States, 2007–2010, and from global body-index software, like PeopleSize Software. They use this to create a stick-figure average for a given-height rider and map it onto the bike to determine geometry and sizing. Lamb and Sheet also looked at differences in strength in men and women from NASA white papers on strength measurements, like this one, to determine stiffness and compliance of frames.

Lamb says that the data indicates that a higher proportion of a rider’s power comes from the legs in a woman than in a man. It also indicates a longer leg length to torso relationship in women than in men. Based on this, they are testing steeper seat tubes on women’s bikes for possible inclusion next year; they test prototypes with their Sunweb team athletes.

Lamb says, “We seek out a compilation of sources to look at everything that we can find. There will be people out of the bell curve. We want to make a full bike that appeals to a woman and that she can sit on and feel comfortable and balanced, and we found that, to put a woman in an optimal position, a slightly different frame geometry is required. We asked: What riding position will a woman be in? Where does she need stiffness? Where does she need compliance? We figure out what is needed and build it from the ground up for women. LIV bikes have a unique carbon layup, and everything about it is a unique bike.”

Early in the 2017 season and spring classics, Team Sunweb riders were on the LIV Envie (an aero road bike meant for flat, rolling races) and the team won Omloop Het Nieuwsblad (Lucinda Brand) and the Tour of Flanders (Coryn Rivera) on it. For the Tour of California, they rode the Langma—a climbing bike with some aero enhancements given the Tibetan name for Mt. Everest.

After looking at data on shoulder width, pelvic width, hand breadth, and hand strength, LIV/Giant came up with, among other things, a dynamic saddle fit method of putting the rider on a bike and have them pedal for a minute on a special saddle. That determines the tilt of the saddle as well as its width and shape. LIV saddles come in either “Forward” or “Upright” models; as a lot of women ride with their pelvis tipped back, Upright saddle designs are meant to accommodate them, while Forward saddles are for riders pedaling with a forward pelvic tilt. LIV bikes have slightly narrower handlebars and slightly shorter cranks than men’s models, and XXS and XS sizes are available in some models. LIV S bikes get 165mm cranks, M sizes get 170mm, and L bikes get 172.5mm, which is the maximum length available on a LIV.

This is a small sampling of how bike companies are trying to make bikes that women like to ride and will buy. There is clearly no agreement on what data to use, what the data shows, and how to design bikes to accommodate the most women. However, in answer to one of your questions, Peter, in-depth studies have indeed been done with regard to bicycle geometry looking at differences in body proportions in women vs. men. As for your other question, clearly some companies are doing more that “shrinking and pinking” bikes for women and are making a serious effort to come up with bikes that improve a woman’s ride experience based on hard data.
― Lennard