What Does ST Stand for on an ST225/75-15 Trailer Tire on a 5th Wheel Trailer

Question:

You recommend a 6-7 inch wide rim for tire size st225/75/15.......what would the ST stand for....small trailer? I have 225/75/15 on a 40ft 3 axel 5th wheel mallard. Would i want to use these same tires?

asked by: Mark S

Expert Reply:

The ST stands for special trailer. ST tires need to be used on trailers because they are built with a thicker sidewall when compared to passenger vehicle tires. This is because trailer tires are designed to handle more vertical load and not meant for the lateral stress associated with a vehicle.

Any given tire will actually fit a range of wheel widths. An ST225/75-15 will fit 15" x 6", 15" x 6-1/2", and 15" x 7" rims.

It is recommended to use the tires specified by the trailer manufacturer. This information should be in the manual that came with the trailer or on a sticker somewhere on the trailer.

Any given tire size will have different load ranges available. For example in size ST225/75-15 you could use a load range C, D, or E. Each of these has a different capacity. Load range C in this size is rated for 2,150 pounds at 50 psi. Load range D is rated for 2,540 pounds at 65 psi. And load range E is rated for 2,830 pounds at 80 psi.

You want the combined capacity of the tires to exceed the gross trailer weight. But going with tires that are rated well above the gross trailer weight capacity will not increase the capacity of the tires. I have included a link to the tires we have in size ST225/75-15. I have also included a link to our help article on trailer tires for you.

expert reply by: Michael H