!4x8 was no problem. Ground clearance was fine. I'm running a 15x6 now also with no problem. Break in with th 100 was a breeze. Per instructions ran it very rich first tank full (4.5 turns out or so) then gradually leaned it out over the next 7 tanks full. Still running slightly rich and I'm on tank number 20. This engine is the easiest starting an smoothest running, I've ever owned. Fuel is Wildcat 20/20 and since the manual didnt specify a break in prop, I used the reccommended 14x8. Hope this helps.

Jim