tire size

all of the above

As wheelie pointed out, with great incite, all of the sizes may be used. The real question is what size tire fits the rim you have the motor laced in. I would take it to a bike shop and find out what size tire fits the rim. I am sure they can tell you just by looking at it if it is a real bike shop.

Grandpa Chas S.

I use a 1.5 on mine.

http://www.nashbar.com/bikes/ProductDisplay?storeId=10053&langId=-1&catalogId=10052&productId=175566