Tire Size Calculator
Invalid metric or imperial size
Invalid metric or imperial size
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Not sure if a size will fit — or throw off your speedo? Text us and we’ll confirm the right setup before you buy.
Text 306-361-4412How to use the tire size calculator
Enter the size on your tires now and the size you are thinking about. The calculator compares the two and shows the difference in overall diameter, width and sidewall height, and how far your speedometer will be off.
Tire size comparison: how the height is worked out
Take 275/65R18. The sidewall is 65% of 275 mm, which is about 179 mm. A tire has a sidewall above and below the rim, and an 18 inch rim is 457 mm across. Add them up and a 275/65R18 works out to about 815 mm tall, or 32.1 inches. These figures are calculated from the size, and real tires vary a little by brand and model.
Common questions
What do the numbers in a tire size mean?
In 275/65R18, 275 is the tire width in millimetres, 65 is the sidewall height as a percentage of the width, and 18 is the rim diameter in inches.
Will bigger tires change my speedometer?
Yes. A taller tire covers more ground on each turn, so the vehicle is moving faster than the speedometer shows. Going from 275/65R18 to 275/70R18 is about 3.4% taller, so a reading of 100 km/h is about 103 km/h on the road.
Can I enter inch sizes like 35x12.50R20?
Yes. The calculator takes metric sizes like 275/65R18 and inch sizes like 35x12.50R20. Type the three numbers into the three boxes.
Does the calculator tell me if a tire will fit?
No. It compares the two sizes. Whether the new size clears depends on your vehicle, the wheel offset and width, and any lift or levelling kit. Text 306-361-4412 with your vehicle and we check the fit before you buy.
More detail: what changes when you change tire size. Changing wheels too? Try the wheel offset calculator.