i recently changed my 44 tooth to a 40 tooth on my 70cc 2 stroke. sounds like a small change but it makes a heck of a difference. i get about 5 mph more on the top end and on the bottom end i can tell no difference. still climbs hills nice. i think the best part is the engine dosn't have to work as hard. to run at 25 mph it purs and is not pushing the engine hard at all which means less vibration and a longer life. top end is 35 mph however i like to cruise at around 27 to 30 mph. definatly a modification that was worth every penny.