What's new

How did tire sizes end up mixed English/metric? (1 Viewer)

Dennis Nicholls

Senior HTF Member
Joined
Oct 5, 1998
Messages
11,396
Location
Boise, ID
Real Name
Dennis
This puzzles me. Tires are not sold in the English (inch pound) system of measurements, nor in the metric (cm kg) system, but rather in some mixed system. For example, a typical tire may be sized as 185 - R60/14, where the 185 is the number of millimeters of carcass width, the 60 is a unitless ratio, and the 14 is the number of inches of rim diameter. What flaming genius decided to mix measurement systems like this? :confused:
 

Jay H

Senior HTF Member
Joined
Mar 22, 1999
Messages
5,654
Location
Pittsfield, MA
Real Name
Jay
The same person who made bottom brackets on bikes English Threaded or French Threaded or Italian threaded :)

And it's tyre for those folks :D

Jay
 

PaulT

Supporting Actor
Joined
Oct 28, 2002
Messages
932
The P-Metric System was developed in 1976 and is the 'US version' of the Metric tire sizing system for passenger vehicles.

It is a conversion of the alpha-numeric system of 1968 in which the width used to be specified in inches. The rim size, however, remains in inches (for some reason??).

In Canada we typically use P-Metric and include the European Metric Service description at the end to specify the load index and speed rating.

For example:
P215-65R15 89H
reads
Passenger Car, 215mm Width, 65 Aspect Ratio, Radial, 15 inch rim, 1279lb load, 210kph/130mph max speed.
 

Users who are viewing this thread

Forum statistics

Threads
356,818
Messages
5,123,881
Members
144,184
Latest member
H-508
Recent bookmarks
0
Top