Women vs. Men's bike geometry
 

I finally did it!! My wife is convinced on cycling and wants to get a road bike. We want to complete a triathlon so that's part of the motivation but she is really serious about a road bike as well. My question is this: Does the difference in geometry affect the ride so much that i would HAVE to get a womens bike or can i get her a small mens road bike? I've been looking at my options for road bikes and have decided to start off with a used bike probably off of craigslist for now but women's bikes are slim pickings so would getting her a small mens road bike be a big no no or will it pass for the time being?

WSD is almost all marketing, depending on the country you are in and ethnicity a typical woman may well be the complete opposite to what the different geometry implies. In South East England there was a large study of height/leg length and it was clear that on average a 18-25yr old woman there has shorter legs as a proportion of their height than the men in the group. Yet the WSD bikes are all set up for longer legged women. The reality is that this actually equates simply to a less aggressive set up with a much higher head tube which may or may not be what a woman wants. If they do they can get it from a mens "sportive" bike anyway.

Women do have different sit bones and tend to have narrower shoulders, so a different saddle and narrower bars would likely be sensible if you buy a mens bike, otherwise a bike that fits is all you need.

She needs a bike that fits correctly -- it may or may not be WSD.

Avoid a "traditional" women's bike (i.e. one with a double-down tube and no top tube).

Some bike shops will push something called "WSD" which stand for woman-specific design. Generally speaking WSD is just marketing BS.

Get her a bike that fits HER properly.

WSD bikes are often the same geometry as non-WSD bikes. Trek WSD bikes are H3 geometry. But WSD bikes also often have different bits: narrower bars with perhaps shallower drop, shorter stem. Women typically have smaller hands than men and some brakes/brifters may have better size for women. I hated SRAM double tap because I had to really reach to shift from small to large front ring. Sometimes, you might also see shorter crank length. Whatever fits best is what she should get.

Your wife's bike purchase should be a "we" or "she" event, not a "you" thing.