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What Do The Letters Mean in the ST205/75D15 C Tire Size on My Camping Trailer


I have ST205/75D15 tires on my camping trailer. What does the D after the 75 stand for, I thought it was the load range? I dont see a load range listed on the tires but the tag on the trailer says ST205/75D15C. Does this mean they are load range C tires?


Expert Reply:

On a trailer tire labeled ST205/75D15 C, the ST stands for Special Trailer which means it is designed for use on boat and utility trailers. The 205 is the section width of the tire in millimeters. The 75 is the aspect ratio (or section height). It means the section height of the tire is 75% of the 205 mm section width.

The D is the designation for the internal construction of the tire. The D stands for diagonal or bias ply construction. That means the tire body plies inside the tire will crisscross.

The 15 is the wheel diameter in inches and the C after the tire size will designate the load range. The load range C is a 6-ply rated tire. The maximum load rating on the load range C tire in the ST205/75D15 size is 1,820 lbs at 50 psi. The load range of the tire might not be right after the tire size, but somewhere along the sidewall of the tire there will be a marking like load range C or L.R.- C. I am including a picture that will show a tire and where the load range is indicated on the tire sidewall.

You will want to make sure and inflate the tires on your trailer to the maximum 50 psi.

I am including links to FAQ pages on trailer tire information.

click to enlarge
expert reply by:
Jeff D

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