posted December 16, 1999 07:00 AM           

For a "P215/70R15":

"P" is for Passenger tire and indicates that the size and load information is generated by the Tire & Rim Association of America. "LT" is light truck in T&RA. If there is no letter before the numbers start, it is usually under the auspices of the European Tire and Rim Technical Organization (ETRTO).

"215" is the nominal section in mm at 70% rim width. So, ideally, if that tire is mounted on a rim that is 70% of 215 mm, that tire would be 215 mm wide.

"70" is the aspect ratio of the section height. Such that the design section height of the tire is 70% of the nominal section.

"R" is for Radial tire (can also be "D" for bias, don't ask me why).

"15" is the diameter of the rim.

This infomation can be used to find the "average" size of a tire where the section width is ~215mm, and the outer diameter would be 15"+(70%)(215 mm)(2). Or you can check the T&RA or ETRTO yearbooks listing the design dimensional and load data for each tire size (no necessarily actual).

posted December 16, 1999 02:33 PM           

215 - width. Wider usually means better handling; narrower usually means better economy and snow traction.

70 - a ratio for tallness of the tires, from donut hole to tread. Higher numbers usually mean better rides or can soak up more rough road shock. Lower means less side-to-side play and better handling.

15 - smaller wheels take less energy to keep going. Biggers wheels soak up bumps better.