Derrrr! I don't know why I didn't post these:
http://www.pro-lineracing.com/prolin...1062/1062.html
They are listed for truck, but they will fit just fine on the buggy. The outer diameter is 3.6", so they're almost identical in diameter to buggy tires, so no gearing changes needed. They are wider, 2.3" compared to 1.9". I have these on my RC18T for the street and they grip great and wear well too.