How do I calculate the size of a space saver spare wheel and tyre?

I am looking to purchase a slim fit spare wheel of the smallest size I can as I do not have a spare wheel but I cannot find the overall size of a wheel including the tyre I am looking at a 15" diameter wheel but how much do I add on for the tyre so I get to the full diameter, is there a formula?

Asked on 31 May 2024 by gerry1945

Answered by David Ross
The tyre size as quoted by retailers and stamped on the sidewall will provide you with this information. As an example, a 205/65R15 tyre has a width of 205mm, and the 65 is the height of the sidewall as a percentage of the width, so in this case it would be 65% of 205mm = 133.25mm. On a 15-inch wheel (381mm) this combination would be 381mm + 133.25mm + 133.25mm = 647.5mm.

However, it is crucial to ensure that the spare wheel is large enough to fit over the brakes of your vehicle. We would suggest looking at retailers such as who provide a range of spare wheels designed to fit a range of vehicles.
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