Tyre size comparisons

[Roy Evett]

Hi, Just finding my way around the website really.

I came across an american tyre website where there were a number of different unanswered questions regarding tyre markings. I did some calculations and submitted the following to the tyre company and they published it.

So I hope it is of interest to someone.

A metric tyre is calculated as follows:- 265 x 75 x 15 tyres:

265mm (10.43 inches) wide x 75% of 265 (aspect ratio) = 7.82 inches high (rim to tread surface) x 15 inch (wheel).

A USA size would be calculated as follows:- 32 x 11,5 x 15.

32 inches tall (from the ground to the top of the tyre) x 11.5 inches (291.98mm) wide x 15 wheel.

The height from rim to tread surface (termed aspect ratio in the 75) is actually 8.5 inches. (Tallness 32 inches – 15 inch rims = 17 divided by 2 = 8.5 inches. (8.5 inches rim to tread on ground and 8.5 inches rim to top of tyre.

Roy Evett (Rocoe)