We fly off a rough grass field. I have tried wheels from 2" to 3 1/2" and found that 3" is the magic number. Smaller causes the wheels to try and push through the grass rather than ride on top of it. This causes a lot of drag and slow runway speeds. Larger than 3" causes other problems. Also be sure to buy wheels with the words Light Weight or Feather Weight on the package. The weight of 3 of these is lighter than the weight of 1 Low Bounce type and well worth the few extra dollars they cost! Have fun, Fast!