Speedo Error with 17's & 18's

Just wondering with the 17"(205/40/17) - 18"(255/35/18) wheel combo how much does it throw the speedo out?
If anyone can work it out what would a true MPH reading be with the speedo reading the following?
70MPH
110 MPH
120 MPH

Check this link out, it has a tyre calculator towards the bottom of the page.

http://www.carbibles.com/tyre_bible.html

Blimey..... I will have to digest all that info later.
lee, don't even start to look at it, by the time the page has loaded, you will have lost the will to live again.

Wat is it

Think its about right with the bigger wheels

[stephendell]

Will read 73mph at 70mph.

seeing as the GTA's have possibly the most tempremental speedos in automotive history and that even when they work they seem to under read by a fair margin in my experience, they may well be more accurate with the wrong size wheels fitted!