Yes it does. The guys I wheel with have 39's and 42's. Just having that 42 on the same obstacle as the 39.5 (I just call them 40's) can make the difference on making it and not making it. This also goes hand in hand with wheelbase. That extra 2 inches can either hinder you or help you. The same goes with a 35 vs. a 37. Every bit helps.
