ckc:joker97: 16 17" and 40 45 profile is ok.
Otherwise life will be hell
Combination of harder shocks, 215/45R17 makes mine handle very well, but you feel every single bump in the road. It depends on what you have to begin with.
But to answer the question, your speedo is probably on the low side on standard wheels anyway. The standards on mine are either 15 or 16, and AFAIK they don't actually bother to adjust the speedo for either of those. With 17s, when I'm doing 100 on the dial I know I'm doing 100 on the radar.
with a 45 profile tyre your feeling every bump probably is the hard springs. hard springs are backbone crushing man. and you can corner a smooth bend better, but as soon as there are bumps in it your car will lift off the road - when the tyre is not in contact with the road there is no acceleration so your speed will decrease.
there is a sweet spot to tyre profile and suspension hardness