So where's the difference in gearing 250SX/Fourtrax 250

I would guess they are the same as far as bore and stroke the tranny on the 250SX is manual I believe and kickstart doesn't the fourteax 250 have electric start too? or is it a 250X?

Ok Then with the extra info you put up I would say the rear ratios ar different

True bore and storke are the only difference. I would say the gear ratios in the tranny as well as the rear are different trikes are a little lighter and would not require a lower gear ratio to get it to speed