Meaning of tire Sizes

Found this on discount tire and figured I would post it, I see people asking about tire sizes all the time and maybe this will help. Sorry if its a repost, I searched and couldnt find much on the subject. So here ya go...

The Meaning of the Tire Size Code


The tire size code consists of a string of letters and numbers as follows:

• An optional letter (or letters) indicating the intended use or vehicle class for the tire:
  • P - Passenger
  • LT - Light Truck
  • ST - Special Trailer
  • T - Temporary
• 3 digit number - The width of the tire in millimeters, from sidewall edge to sidewall edge.
• / - Slash Character
• 2 digit number - The ratio of the sidewall height to the total width of the tire as a percentage. If this is missing, it is assumed to be 82%. If the number is larger than 200, then this is the diameter of the entire tire in millimeters.
• Construction of the fabric of the tire
  • B - bias belt
  • D - diagnol
  • R - radial
• 2 digit number - Diameter in inches of the rim that this tire is designed to fit.

Example
The tire might be labelled:


P195/55R16

• 'P' these tires are for a passenger vehicle.
• 195 – the width of the tire is 195 mm at the widest point.
• 55 – indicates that the height of the side-wall of the tire is 55% of the width - 107 mm.
• R – this is a radial tire.
• 16 – this tire fits 16 inch diameter wheels.

 

http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=48

This link helps explain UTQG standards for tires also (tread wear, traction and temperature ratings)

 

Which is also accurate only when comparing tires of the same manufacturer.

 

Yeah, that's a good catch. Even though it's supposed to be a standard it definitely varies from manufacturer to manufacturer.

 

When they came up with the Uniform Tire Quality Grade (UTQG) was that the Uniform Tire meant the same manufacturer