by AlMac » Fri Jan 04, 2013 6:58 pm
I am 180cm tall. Not sure about inseam, but I am proportioned within the normal range.
I've been riding a Giant Defy Medium/Large for 3 years. It is close to a perfect fit for me. I found the Medium clearly too small.
At your height, you need to ride both and then decide. I would absolutely not be just buying the Medium without riding the M/L.
A bike shop can guide you for fit, but only you can make the final decision. To do that, you have to ride both.
Often it is very obvious which is the better fit (fortunately in my case that is how it has been on each of my bikes). But also bear in mind that you might need to add or take a space out or swap or flip a stem to get it just right - not necessarily go up or down a size.
A proper bike fit by a professional bike fitter will tell you what size frame you need (so generally not your bike shop employee by just looking at you) and you can work with that as a base and change things like saddle position, stem and bars.