They may alter your speedo reading. if you have a sat nav, check the speed on your clocks against the sat nav before and after you change the diameter of you wheels. this will tell you the differnce (helps alot as speedo's on corsas are always a bit slower that reality. I know a guy who got done by a speed camera because his new wheels.
I don't know of hand your best bet is a sat nav because that works out your speed by gps. or if you know some one with a standard car drive next to them at twenty on a car park and note the difference.
my corsa b had 15"s on and there was 5mph discrepancy comapred to my sat nav, think the sat nav was like 5mph slower than what my dashboard was reading, but there was several times when i was followed by a cop car and went through loads of speed camera's at 30 (according to the corsa speedo) and didnt get pulled or flashed,
now in the clio, got the same wheels on, the original on the clio were 14"s, and its only a 2mph discrepancy
p.s. will go out and check now what my tyre size is as im off to the burger van lol
every speedo is allowed something like a 5% error in speed reading. this is why you can ask for the speed cameras calibration certificate and get off with speeding if it hasn't been calibrated in a certain time before you were caught. you can blame it on your speedo and be made to get a new mot instead of points.
i only said there was a difference. Didnt say how much it would be.
but the circumferance is what makes the differance
17 = 53.4"
and thats just the alloys the tyre choice can alter this in multiple ways (low profile tyre's etc)