#TechTip: Tire Sizes 101

Tire sizes can be confusing the first time you have to read them, so here’s a quick run-through:

22 Feb 2016

Tire sizes can be confusing the first time you have to read them, so here’s a quick run-through:

What you'll see on the tire

This is a pretty standard example of what you’d find displayed on a sidewall. There are three measurements on most tires, and they refer to the following:

The width of the tire (in mm)
The sidewall height (displayed as a percentage of the width)
The type of tire and the wheel size

Example:

Here you can see the width is 245mm or a little over 9.5”.
The sidewall is 40% of 245mm wide, putting it at about 98mm on each sidewall
The “R” stands for Radial, and the 18 represents that the tire is for an 18” wheel

Common Misconceptions

“A certain sidewall size is always the same”: Wrong. Remember that the sidewall is a percentage of the width, so a 205/45 will have less sidewall than a 295/45.

“All tire widths are created equal”: Wrong. Different manufacturers have their own biases towards actual measurements. You may find certain brands run consistently narrower or wider than others. Sidewalls should be consistent, however.

What’s your tire size? Post it below!

Comments

33x12.50R20

175/80-14

was running 205/40/R17, now have put smaller wheels on and have the good old 195/50/R15 tyres

My chance to repost a question I asked a few weeks ago which I didn’t got many aswers for:

A question to the wheely clever guys (get it?)

CTzens, I come to you with an important question: I have a set of 18x7 inch rims. I want to put 225/40R18 tires on them. Stock would be 215/45R18. Would you recommend it to do it? The clearance should be no problem. My concern rather is about the lateral dynamics because of the changed side wall geometry. Do you think it will affect the performace for the better, the worse or not at all?