[Munchskull]

You can look at wheel size in two ways. The first is ground clearance. If you have a bump or feild obstaclesthat you need to traverse then you want to goconsider wheel size so you do not bottom out. When choosing a wheel size for clearance I would always go with the smallest size that works.

The second way to think about wheel size is it is the the final stage of gearing. For a give gearbox a 8" wheel will go twice as fast as a 4" wheel. So the smaller the wheel the less you have to gear down. The less you have to gear down the smaller the gears, and smaller gear and wheel weigh less.