Since I switched out the bikes I haven't really gotten much chance to ride. I have no idea what this is but when the bike climbs a hill not about half way up a really steep one the engine changes sounds but the bike doesn't speed up or anything. It is going wide open and just changes the sound it makes. It did not do that with the 2o" wheel. It seems to run a little faster on the flat but the hill climbing is the same I think.