Originally Posted by
dougpgreen
Its interesting that you think your 5-10 husband needs a medium as I am 5-10 and my wifes medium 5.0 doesn't fit me as well as my large. It got me wondering if there is a difference in the carbon and aluminum frame geometry as most of the posts I have seen recomending sizing down come from people on 4.0s. I check the specs on both in a large and YES, there is a difference in specs on many of the dimensions. Some are subtle but some are significant, enought to change the way the bike feels. It could very well be that I (and perhaps your husband) would fit better in a 4.0 in a medium, while fitting better on a 5.0 in large. It is also interesting that the x 4.0 comes in sizes XXS-XL, while the x 5.0 comes in XS-XXL. The bottom line is not to assume that sizing advice on one transfers to the other, particularly if you are near the borderline of a size range.
I think 5'9-5'10 is a tricky height. It's M in some bikes and L in others, 54 or 56. We will definitely have to try both sizes. Right now, only M is available in the same store where I have bought my bike.
For 5'1 Specialized recommends either XS and S. I tried S yesterday. It was doable, but XS definitely fit better. S somehow felt like a much larger bike.
I guess the key is trying both adjacent sizes.