It's the same as the gear ratio is a gear ratio threads that are always on here. No one can really explain why, but it does make a difference. I believe a larger front driver pulley is better on the top end of the straight away and the smaller driver is better at acceleration on the low end out of the corners.
I like the larger belt wrap idea where it is putting less stress on the belt. I recently read a Facebook post talking about this very thing where a Yamaha should be on a front driver 16t or larger for a laydown, (we normally run 14t to 16t), with a 20mm belt because the belt isn't meant to turn that much RPM and a the larger wrap doesn't create as much heat, and stress. Now if you go to the larger 30mm wide belt it can take more abuse.
In my animal sprint enduro I normally run a 26t and 27t front driver and rear gears in the lower 70's. But I use different drivers more for engine placement, because there isn't much room between the seat and clutch and the engine needs to sit in a certain spot. I also have at least 2 different belt sizes I have to pick from to use. I have to do the same thing with the Yamaha laydown, because of the pipe and clearance issues.
