Good question. The outdoor industry trend has been to "shrink and pink" bikes, skis, packs, kayaks, and even energy bars. In most cases, the women's-specific evolutions are welcome improvements. Then again, Lindsey Vonn just walked away from the Olympics with a downhill gold that she earned on men's skis. So before you rush out and buy a girl's bike, take a minute to evaluate your physical size and the intended use for your gear.
With bikes, for the average U.S. female who is 5'4", there are some distinct anatomical advantages in using a women's-specific saddle, a shorter stem, and a smaller frame. But that doesn't necessarily mean a 5'10" woman (like me) should do the same.
And in some instances, changes in bike geometry to accommodate the not-necessarily-true axiom that women have longer legs and shorter torsos than men haven't always led to bike designs that yield higher performance.
In the case of Trek's top-of-the-line carbon Fuel 9.8 WSD ($4,720; trekbikes.com) cross-country racing bike, the designers found that when they shortened the top tube to accommodate the size discrepancy between men and women, that change also shortened the bike's wheel base, which made for a less-than optimal ride for their female racers. To mitigate the issue, Trek took the geometry from the men's Fuel 9.8, added two smaller frame sizes, 14.5" and 16.6", and shortened the handlebar stem. The result is a bike that, other than the women-specific saddle, shorter stem, and two smaller sizes, is exactly the same as the men's version.
How does the Fuel 9.8 WSD ride? Before I took the 17.5" frame (which is the largest in the WSD line and the second-smallest in the men's line) for a test ride, the Trek specialists at New Mexico Bike & Sport (nmbikensport.com) helped me set up the proper suspension for the Fox front and rear shock--a must-do before you ever test or buy a bike. Then I took it for a spin near Placitas, New Mexico. The featherweight Fuel cornered beautifully and was so light that I more easily motored up singletrack, even through an occasional patch of thick February mud. The custom-dialed rear and front suspension kept my wheels on the ground and my rear-end on the comfortable Bontrager Race women's-specific saddle--a much better place for it to be than, say, tangled with an oncoming cactus.
My takeaway after the test drive: Don't worry too much about the gender-specific label. If the bike fits, ride it. Especially if it's a ride like the Top Fuel 9.8 WSD.