The Mystery of Tyre Numbers


It annoys me every time I have to order a new tyre that I am completely in the hands of the bloke wielding the jack. I know nothing of the mystical digits on the side of my booties. Looking into this, I did a bit of delving. Thought I’d like to share.

Apparently the basic size and shape of your tyre is embossed on its side wall in an internationally accepted formula. Take this formula for example:


As in all cases the number after the slash is the height-to-width ‘aspect’ ratio of the tyre section expressed as a percentage.. The letter ‘R’ denotes radial construction (as opposed to those simple, classic crossply jobbies). Letters preceding the ‘R’ indicate the tyre’s maximum operating speed.

The number after the R is the diameter of the wheel in inches, and an additional code, between the numbers 65/119, indicates the weight that the tyre can support at maximum speed.

Confused? Me too. But you can find meaning in the most arcane of numbers out there.