What are the differences between men's and women's bike frames?
Why do women's bikes have a diagonal bar in the frame instead of a horizontal frame? Is this the only difference?
Sorry if this has been asked (but I cannot find it by searching) and I also just cannot think of a reason why.
@WTHarper just casually asking someone, they mentioned it might be dress related...skirts or dresses might be more accommodated with the diagonal bar...but that was a guess...
Way back when safety bikes were becoming popular, women wore skirts. Skirt lengths were to the ankle. The dropped top bar made getting on possible while maintaining respectability. Women were considered too fragile to risk hitting the top tube, hence the slanted bar. The trend continued even long after women stopped riding in long skirts.
Modern WSD (women specific design) geometry differs from conventional bike geometry. The difference goes beyond just size. Whether it is needed depends on who you ask. While some women may be smaller than the average male, many are as tall; height is not the only issue. Many women have a different leg to torso ratio than the male average and the frames are built to fit that difference. This is not to say that a women needs a female specific frame or that a male wouldn't fit on a WSD frame. It all depends on the individual physical traits of the rider.
Differing leg/torso ratios are handled by top-tube sizing for any given seat-tube length. I think the OP is asking about step-through frames-- not just sloping top-tubes like on compact geometry frames for road bikes.
mikes: Agreed. I just thought "long after women stopped riding in long skirts" was a tad bit overstated.
I have seen no evidence that leg to torso ratios actually differ by gender. It is my understanding that this is a myth and that there is more variation within gender than between gender (i.e., not statistically different)
@William here is a general article http://www.womenscycling.ca/blog/georgena-terry/womens-body-proportions-different-mens/