By Roger Marble
A question came up about the maximum speed recommendation as published by Goodyear, Michelin, and Bridgestone for tires in RV use. To help clarify: Many times the “application” or use of an item results in it having additional or different limitations or ratings.
If I have a tire that is a 225/75R15 and inflate it to 35 psi, How much load can it carry?
• If the intended use is on a passenger car it is rated for 1,874 lbs.
• If as a single on an LT it is rated for 1,445 lbs.
• If as a dual on a LT it is rated for 1,315 lbs.
• If a single on a trailer where having passengers in the trailer is actually prohibited, 1,760 lbs.
• If in a dual application on a trailer, 1,570 lbs.
Part of the decision process for a tire’s capacity in each of these different applications includes such things as: Will the vehicle carry passengers? Is the “Reserve Load” of the tire in the application normally close to zero or maybe 10%, or normally closer to 25%?
An obvious example where the application affects the load capacity is well established in the use of “P”-type tires on a truck, trailer or multi-use vehicle such as an SUV. In these applications the load capacity is reduced by industry standards by dividing by 1.10, so the 1,874 lb. capacity becomes 1,703 lbs.
For heavy trucks there are published guidelines that allow an increase in load capacity if the maximum speed is significantly reduced. As the speed is lowered, the load capacity can be increased up to 16% with no increase in inflation.
Similar to above, if the tire is made for a specific market a tire company may have more demanding requirements on the tire during the development process. An example might be if the tire was being made for a market where the speeds and ambient temperature were both very high, the tire might require a more robust construction. Another example might be providing a special tread rubber if the tire was to be used at extremely low temperatures where the tread rubber might even crack if a “high speed”-rated tire tread were used.
Tires are much more complex than many people suspect. Ideally, an owner would be more informed and knowledgeable about tires and their limits and capabilities when making a purchase. They are much more than just “round black” things that almost no one “wants” to buy.