I've got a B3030 with ag tires and I want something less aggressive, either R3 or R4. The existing tires are 7-12 front and 12.4-16 rear. I found a set of tires nearby that are 27x8.50-15 front and 41x14-20 rear. Diameters of old tires front/rear are 24/37.6 = .64 and new front/rear are...