
Originally Posted by
zoom-zoom
I am about a quarter inch taller than you, but with shorter legs. I think the 51 is a size larger than what you'll likely fit best. My previous road bike was a 2010 Synapse 48cm and was a good fit. I would not have wanted to go bigger. For you to fit the 51 you'll likely need a really short stem, which could make your bike handling less than ideal.
When you're in between sizes as the OP might very well be, one's overall inseam tells only part of the story. The more important question often is whether her femurs are relatively (relative to her inseam that is; not relative to women in general) long, relatively short or average. It's femur length that dicates how far back or foward her saddle needs to be to get her knees in the appropriate position relative to her pedals. If she has relatively long femurs, chances are she's going to have to put her saddle farther back which will, in turn, effectively lengthen the top tube of the bike. If she has relatively short femurs, then her saddle may have to be set forward a bit, which will effectively shorten her reach to the handlbars.
So, if I were in the OP's position and was trying to decide between two sizes, I'd try to get the LBS to do a preliminary fitting on the bike prior to a test ride. Set the saddle height and fore/aft position and then see how the bike's cockpit feels.
Live with intention. Walk to the edge. Listen hard. Practice wellness. Play with abandon. Laugh. Choose with no regret. Continue to learn. Appreciate your friends. Do what you love. Live as if this is all there is.
--Mary Anne Radmacher