You don't have to know the geometry - you have to know what feels right. The LBS has to know the geometry![]()
Take your time. Take mulit-mile test rides and keep trying different geometries so that you get a sense of what you will "get used to" and what is still just not right. (I got a road bike once that I thought I would get used to. I didn't. No, I didn't get properly fitted - it was a very good deal and it did feel fine to ride for a little while, so I bought it... but after thirty miles I got all cranky and mean.... again and again. This has made me reluctant to go for a road bike.)