I know that there is a way to work this out cos have known people to configure traction control settings with the use of some very clever algebra! Well, that was never me at school so I need an answer to this question please :

Q. I have 17" wheels, so what difference does that make to the reading my speedo gives me? Am I actually going faster than what it says or slower?

Answers on a post card, or maybe in here!

You will be going slower than speedometer reads...

Not exactly a postcard but...

If you are using a 205/45/17 or a 215/40/17 tyre then the rolling radius is exactly the same as the original 195/60/15 tyres. So no change.

If you're using 205/40/17 (a more common tyre) then the total wheel diameter is slightly smaller and the speedo will over read.

arent u going faster?
im not using algebra, just logic. ur tires are bigger so they will cover longer with every revolution, so u will be going further than with smaller tires. therefore u will be going faster.
Im pretty sure im right, check the logic out, see if it works in ur head too

but it matters on the size of the tires as well

90t16Saero,
try http://secret-secret.com/turbo/DIY/tirecalc/turbotire.html

A larger wheel/tyre goes round slower for a given road speed compared to a small tyre. The speedometer reads the rate the wheel is going round.

Nice one guys, according to the calc my speedo will be reading approx. 3% too fast! Damn, now i have to go even faster just in case!

who was the first one to call it?
me