Lennard Zinn gets an insider look at brands’ complicated relationship with sex-specific biomechanics.

Remember when we were told that women had longer legs and shorter torsos (and wider sit bones) than men, and that their bikes (and saddles) had to reflect that?

This has not been borne out in my anecdotal experience over 36 years of designing and building custom bike frames, and many bike companies are also seeing the light. None of the top five bikes in the 2017 annual bike count at Ironman World Championships—Cervelo, Trek, Specialized, Felt, and Argon 18—have gender-specific triathlon bikes, but Giant—which sits in the top 10— stands out as having specific bikes sized differently for men and women.

Stephanie Kaplan started as women’s product manager at Specialized and is a fast female rider who just happens to be short in stature. Since Specialized sells more men’s bikes, allocating resources toward women’s-only bikes is a hard position to take. Nevertheless, the company told Kaplan that if her team discovered a legitimate need for women’s-specific bikes, it would come up with the funds to make it happen.

Kaplan’s team started with a book that detailed results of a U.S. Army study from the 1970s, a book she says has been the bible for development of ergonomic chairs and other person-sized equipment, because few organizations besides the military have that much physical-measurement data on so many people. She also gained access to another large data resource when Specialized purchased the Retül fitting system in 2012. For years, Retül has captured anthropometric data on thousands of customers by putting LEDs on body joints, digitizing their location in space, and using that info to perform bikes fits.

When poring over the data, looking for distinctions in limb lengths for women vs. men, Kaplan admits that she “looked into it with my internal bias, trying to find that they were there.” Despite this, she and the other Specialized product managers working on the project found no correlation between gender and limb length, nor 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). “What we were doing before,” Kaplan says, of their previous women-specific bike designs,” was right, based on the information we had before.” But since she says their new fit data no longer supports different frame geometry, she adds, “I’m not going to lie about it so we have a great marketing story.”

The new data consisted of 4,000 Retül fits with full anthropometric data on each client, as well as data from 36,000 Specialized Body Geometry (BG) fits worldwide. Specialized’s BG data consisted of bike-fit only—the locations of the touchpoints of the bicycle in space—and gross body measurements like leg length, but not the detailed anthropometric data that Retül captures—for instance, the length from ankle to knee and knee to hip.

Based on this aggregate data analysis, Specialized is discontinuing frames with women’s-specific dimensions but insists that certain components—handlebars, saddles, and cranks for instance—still need to be gender-specific, even if the frames are not. For tri, the Shiv is not gender-specific.

Interestingly, Giant also looked at lots of data and came to different conclusions: Erin Lamb, the five-foot 10 product manager for LIV (Giant’s women’s brand), comes at it from different personal needs than Kaplan. Lamb and LIV engineer Sophia Sheet studied 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. From it, they created stick-figure averages for given height riders and mapped them onto bike designs to determine sizing. Lamb and Sheet also examined differences in strength in men and women from NASA white papers.

Lamb says the data indicates that a higher proportion of a female rider’s power comes from her legs than that of a man. It also indicates a longer leg length to torso relationship in women than in men. The team also looked at data on shoulder and pelvic width as well as hand breadth and strength. All that data, Lamb and her team determined, showed that there’s a need to build women’s bikes from the ground up—creating women’s- specific frames and selecting components with women’s sizing in mind.

In addition to shorter top tubes, LIV bikes have slightly narrower handlebars and slightly shorter cranks than men’s models. The XS size LIV Avow Advanced women’s tri bike has 160mm cranks, while the S and M sizes get 165mm cranks. Compare that with the Giant Trinity Advanced men’s tri bikes: The XS gets 165mm cranks; the S gets 170mm; M size gets 172.5mm; and L gets 175mm.

Giant also came up with a fit method of putting the rider on a bike and having them pedal for a minute on a special saddle that uses colors created by impressions to indicate contact points—this helps fitters determine the rider’s optimal saddle tilt, width, and shape.

The company’s women’s saddles are generally wider than the men’s. Both their women’s and men’s saddles come in “forward” and “upright” models; forward saddles are meant for riders with a forward pelvic tilt, like the position used in triathlon.

Trek goes at it yet another way. Similar to Specialized, their design decisions are based off of data gathered from their own fit sessions, known as Bontrager Precision Fit. “This is great, representational data of all different sizes and gender of riders that helps steer our engineers and designers,” says Dean Gore, marketing director for Trek. From this trove of data, Trek chose to make no gender distinction, because they found no correlation between gender and frame sizing. Accordingly, Trek offers one set of gender-neutral sizes for its Speed Concept tri bike.

Jim Felt, founder of Felt Bicycles, tells the tale of another brand whose approach to sex-specific design has evolved over time. “We actually were one of the first to enter the [women’s bike] market, but not necessarily because we sought that opportunity,” he says. Felt’s marketing person at the time was a woman, and Felt says she insisted that women need a specific bike with a slight spec change. “I do believe it is a big plus to offer women what they are really looking for,” says Felt.

“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.”

Felt’s senior marketing and communications manager Michael White takes a more statistical perspective on why Felt Bikes no longer offers women-specific models: “Over nearly three decades of research, our engineering and product development team have yet to find conclusive evidence that male and female riders require separate frame geometries to perform at their highest potential.”

While we may have once believed that women tended to have longer legs, shorter torsos, and wider-spaced sit bones than men of the same height, today many bike brands have their doubts, and few besides Giant’s LIV offer women’s-specific frame designs.

Of course there is financial incentive for bike companies to tell us we were drinking the Kool-Aid the whole time: Full carbon frames require expensive molds for each size, and this massive additional expense did not exist when they were selling welded metal frames. But at the same time, with more data now available, we’re seeing brands turn away from sex-specific design toward something more like people-specific design. Though touchpoints like levers, handlebars, and seats still generally fit women differently than men, new models seem to show that a person who needs a longer top tube could be anybody, regardless of gender.

Lennard Zinn is a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Road Bike Maintenance, Zinn and the Art of Triathlon Bikes, and Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He also holds a Bachelor’s degree in physics from Colorado College.