[Joe Johnson]

I have used 1/4" over the years, but I now think 1/8" is enough. Actually, the more rigid your frame and wheels, the less offset you need.

Also, if you use pneumatic wheels, you can play with inflation levels of the center wheels to get more or less rock. In general, lower inflated wheels grip better so there are limits to what you want to do here, but it does give you some freedom.

Joe J.