Rim size increased, speedo error?

[43034]

Evening all, I have recently put bigger rims on my car. Gone from 205/50/16 to 225/45/17 and have just thought about the speedo difference changing. My man maths is failing me and I can't seem to work out whether it will make my speedo under read or over read.

I assume it will make it under read thus meaning I am susceptible to getting caught 'speeding'?

Can any PH maths people help me out here with regards to how much it should be under/over reading?

Thank you very much guys!

[Zebrs]

http://www.tacomaworld.com/forum/tirecalc.php

[Red Firecracker]

Your speedo is now reading 3.7% too slow (or slower than it was before)

[V8Wagon]

When your speedo reads 70mph you'll actually be doing 72.51mph.

http://www.alloywheels.com/Tyre_Calculator

[43034]

Ace!

What a great site this is. Swift response, thank you very much!