I use a ride on leave spreader at work that’s powered by a Subaru ea190v Thanks to a catastrophic failure that destroyed the ignition coil, I had to bolt on a new one. The old pulley that was on the shaft out of the motor was well rusted on, so I just replaced that as well, but with a slightly smaller pulley. I went from a 3.75” pulley to a 3.50” pulley, causing the belt to be a pinch too loose. I have no freaking idea how to size a new belt. So I just get one that .25” smaller? I feel like that’s the right answer, but don’t want to play a guessing game buying a bunch of belts to see what works. It’s fertilizer season, and I’d like it to be right the first time.