With this tyre size calculator you can:
- Compare two tyres; for example diameter and width;
- See the difference a new tyre will have on your speedometer reading;
- See the difference in ground clearance with a different sized tyre;
- Get some guidance about the effect on your vehicle of the new tyre;
- See what equivalent sizes there are to your existing and new tyres;
- See a graphic comparing the two tyre sizes.
You just need to know a few tyre specifications, then hit Calculate. If you’re not sure about tyre specs, then read the Tyre Help.
There is also a calculator to convert tyre sizes to/from imperial and metric and you may also find the Towing Weights Calculator useful.The following general guidance may be of use; check whether it applies in your specific circumstances:
FitmentThe measurements here are calculated from the general tyre specs; in practice, actual sizes will vary a little from these measurements, particuarly offroad tyres which have deep tread. Check the exact specs for your selected tyre in your selected size, and in particular:
- Your new tyre is taller so your speed will read low compared to true speed, Your gearing will now be higher; fewer revs to maintain 100km/h.
- As your tyre is taller, you should check fitment in spare wheel bays.
- You are fitting a significantly wider tyre; you may need a wider rim to suit. In most countries tyres cannot protrude from the bodywork, so consider wheel arch flares.
- You are fitting a smaller rim; ensure this fits your vehicle, especially front brake calliper clearance.
- Your new tyre is both taller and wider than the existing; this will mean it is heavier, with effects on handling, fuel consumption etc.
Australian road rulesFor Australians, the following should be considered with regard to legality but check your specific situation:
- Your new tyre is more than 15mm taller - check that's legal, usually limit is +15mm for cars, +50mm for 4X4s.
- Wider tyre may require wider rim; road regulations may say permitted rim width is +/- 25mm from standard.
- Also check your tyre's speed and load ratings; in most cases the new tyre will need to match or exceed those ratings, except for offroad vehicles which can use N (140km/h) rated tyres.
by Jurgen Loos