[tire]

defanitely get 17s. A 17" tire with a 45mm sidewall will be roughly the same diameter as your tire+rim is right now and wont cause any speedometer problems, or any other of those problems your stepdad mentioned. Id defanitely go with 17s though, youll kick yourself for not doing it later :headbang:

if you are referring to the "45" from 245/45/17, the middle number is not in MM's it is in % of the tread width, which is the 245. So it would be 45% of 245 which is about 120mm.