I guess the question could be is the standover number of 30.86" the actual height of the top tube or the longest inseam measurement suggested for that model. For example if your inseam is 28" - 30.8" the 50 will fit if it's 31" -31.75" then get a 53 smaller than 28 would call for a 47. I know the best way is to actually ride the bike but with so many choices these days it's tough for the Stores to carry every model.