club.liberty.asn.au

Evening all I was just wondering if putting bigger wheels on my car will throw the speedo out at all as I have herd of this happening on other cars when they went up in size is this fact or myth or does the speedo recalibrate it's self with modern day cars

Changing the rolling diameter of the wheels will affect the vehicles speedometer.
Look at the link to the RMS site for what tyre size change is permissible.
http://www.rms.nsw.gov.au/documents/roa ... 9-rev4.pdf

Recently, the wheels/tyres on No.2 Junior's car were updated from 215/45x17 to 225/40x18.
This changed the rolling diameter from 625.3mm to 637.2mm. This was an increase of just under 2%.
As the speedo error at 100kph was 3% to 4% fast, the change actually compensated for the factory error and made the speedo more accurate?
Cheers!

Speedo doesn't re-calibrate itself. You should be looking at the tyre diameter.

Check this site out: http://www.carbibles.com/tyre_size_calculators.html

Bear in mind that in the example above, the change was 11.9mm. This TTBOMK is legal.

I wanted to go from 225/50r18 to 225/55r18 which changes the rolling diameter by 23mm and is not legal, therefore not insured.

Check your road laws, and do your homework before changing tyre sizes.

will the offset of the rims affect much aswell

Offset won't effect rolling diameter (ie Speedo calibration)

Often though, lower offset=wider wheels=different sized tyres which will effect it