Originally Posted by Mike134
do you just make stuff up?
The Industry has minimal standards. Those standards can be found in many of the USTMA manuals. Here is an excerpt from one of them: Replacement tires should be the same as the OE size designation, or approved options, as recommended by the vehicle or tire manufacturer. Never choose a replacement tire of a smaller size or with less load-carrying capacity than the OE tire size at the specified vehicle tire placard pressure.
When the tire industry is talking tire size they are using their familiarity with the use of the word size
when applied to tires.. Here is a listing of designated sizes. The prefix is an integral part of a tire size. Those without a prefix are normally Euro-Metric in size, design and load capacity.
Size designations usually include letters which have the following meanings:
These are prefix letters and part of a tire's size designation.
• P = P-Metric (Passenger)
• LT = Light Truck
• ST = Special Tire for Trailers
• T = Temporary Spare
Letters found within a tire size:
• R = Radial Construction
• F = Self-Supporting, Runflat
• D = Diagonal (Bias) Construction
• B = Belted Bias Construction
• C = European Commercial (Light Duty)
Load range, load index and speed letters/numbers are not a part of a tire's size designation. They are informatory.
Many of the new 2021 standards manuals/regulations are already available on the net. (WWW)