Physics. Rotational inertia of a 700c x28mm wheelset is about the same as 650b x 42. You should be able to accelerate the same to keep up with your buddies sprinting for the county line signs.

So it's not that it doesn't matter, it's just that it shouldn't make a difference.

The additional weight will slow you down. I assume your body fat is still pretty low like when you raced, right?


The main reason I ride 650b fatties is the roads around here can be kinda rough, and I don't want to limit where I ride by road condition.

The real reason not to change is if you're happy with 700c and the tire width limitation (comfortable riding on the tires you're riding on the roads you like to ride on), why go through the expense of changing over? That is, if it ain't broke, why fix it?