My inseam is about 31 1/2" I have been to several bike shops (recommended by local cyclists) I have been told I am in between a 48 and 51. On a 51 I have about 2 inches of clearance when standing over the bike. When I try the 48 I feel cramped and push off the back of the seat. I will get a professional bike fitting and 6 months of free adjustments with the purchase. Of course when you try a bike it is not like you get to take it on a 20 mile ride! I can only go by what they recommend. Free life time tuneups is a great deal! No one in our town offers anything close to that.