Does Tire Diameter Factor Into Speed Rating for Trailer Tires

Question:

I have a 900 lb. pop up camper with one year old 5.30-12 wheels and tires rated for 81 mph. I do not have a spare. I am thinking of buying two more speed rated tires as I plan on taking my camper on an 8 hr trip averaging about 70 mph. I am looking at the Kenda and Taskmaster wheel/tire combo but have a question about towing speed. My tow vehicle has 31 tires. and the 5.30-12s I think have a height of about 21 or 22 inches. Are the 5.30s rated at 81 mph on the tow vehicles speedometer? Or because the 5.30s are smaller would they be exceeding the 81 mph rating because they are making more and faster revolutions compared to the tow vehicle? I hope I wasnt too confusing, I just dont want to push the limits of the tire and risk having a blow out. Also, I am taking my two sons to Big Bend and it is very remote. I want to buy two spares just in case. Thanks,

asked by: Massey R

Helpful Expert Reply:

The speed rating for a tire takes into consideration the overall diameter of it and how many revolutions it would be turning. Regardless of the size of the tire if it says 81 mph as the speed rating that's how fast you could go with using the speedometer of your vehicle as the guide.

expert reply by: Jameson C