I am about to make my first purchase and am looking at flat bar road bikes. At almost 5'1", it seems that 13" is my size. However I recently spoke with an experienced biker, also my height, who chooses to ride a 15". She likes the larger wheels and also that the bigger bike allows her more room to extend her upper body. Does anyone have an opinion on riding a bike that is your size versus one that is bigger? I took the 15" for a spin (Marin Mill Valley) and liked it but there was no 13" available and I wonder if I'd be making a mistake to go for the larger size.