if you get 18's does it effect your transmission, i know it changes your speedo but does it promote premature tranny failure?

 

Actaully if you get the correct Sized Tire for the rim your Speedo will still be accurate, and I would think there should be no additional wear on the Tranny. Basically if you match the outside diamter of the rim / tire combination to the factory the rotational forces are exactly the same. Just a bigger Rim and lower profile tire......