Originally Posted by
cyclic_eric
I am also 5'10", and my inseam is 33". 56cm bikes seem a bit large to me, I prefer the nimble feel (in my opinion) of the 54 or 55cm bikes. The decision is also related to the type of roads and riding you plan to do. This all is a matter of opinion, but short quick turns and rides, smaller bike; longer rides, bigger bike. Try different sizes if you can.
When people state the frame size, you really need to find out how they measured it. Generally, the seat tube length is easy to adjust - just raise the seat up or down. The top tube length is more difficult - you can alter stem lengths, slide the seat fore and aft, and/or change the reach on the handlebars.
I second this.
I'm also 5'10" with a 33" inseam and prefer 53/54cm bikes. 56 cm bikes felt a little stretched out for me but I also prefer to run about 8.5 - 9 cm of saddle to handlebar drop. Similar to cyclic eric's comment, make sure to check out the geometry and compare reach/stack along with the top tube for the bikes you're looking at.