They are 18" and i didn't really notice any change in the drive actually the car is more stable, since u go from 16" to 18" you have to put low profile tires which improve the handling. The only thing that u might notice a little bit is just feeling the bumps and holes more, it's going to be roguh basically on bumbs and holes. other than that it's perfectly fine, i always get on the highway and i have driven over 80mph it's absolotely fun but make sure that the balancing for the tires is done right.
