I recently had to replace my original rear tire for state inspection passage. I had a hard time finding the exact size with any variety. The dealership sold me a 170 only to have THEIR service dept. refuse to install it because it was not the original equipment size. I was **** because of the waste of time. I ended up getting the original size after a 2 day wait with only one brand available (Bridgestone Exedra), but I too would like to go bigger. I know the 170 will fit...and if the 180 is indeed safe, I will jump to the fatter ride as soon as possible.