Well, i originally had the 14" steel wheels on my car, which had whatever profile on them, either way when i put the SX alloys on with that profile (Which i believe to be standard) i know the speedo reads SLOWER than what i am going, by 3.1% meaning when speedo reads 60 i am doing 61.9mph.
Thinking about it i think it was 55 profile, gimme 5 and i'll go check!