Recommended 4.80x12 Trailer Tires for Speeds Over 65 MPH

Question:

Sir: I am building a Harbor Freight 48 x 42 inch utility trailer running 4.80 x 12 wheels and tires, with a B load rating. My reading of the tire sidewall is that these tires have a load capacity of 785 LBS each, when inflated to the recommended 60 PSI cold. With that in mind, I calculate that the combined tire weight capacity for this trailer would be: 785 LBS x 2 = 1,570 LBS. In reality, however, the trailer is going to weigh approximately 175 lbs when completed and I will be towing equipment on it weighing no more than 300 to 350 lbs. - for a total weight of roughly 500 to 550 pounds. F.Y.I. - the weight capacity of the trailer itself is just shy of 1,100 LBS. With that in mind, and a total weight loading of approx. 1/3 of the tires capacity - shouldnt these tires - properly inflated to 60 PSI - be capable of speeds a bit higher than the 65 mph limit which I assume is calculated by the manufacturer for those tires at MAXIMUM weight capacity? I ask because running 65 mph on the interstate with traffic flowing 10 to 15 mph faster these days in many parts of the country seems a bit risky. While I dont want to run faster than necessary, running 70 or so to at least keep up with the flow of traffic is very desirable from my point of view... Anyway - I would appreciate your thoughts. Thanks!

asked by: David H

Expert Reply:

A trailer's weight capacity is dependent on the weakest component in the system which could be the axle, the springs, the coupler or any other component. Normally tires are rated higher than the wheels they are attached to so that will likely reduce that rating as well.

The speed rating of the tires has nothing to do with the load capacity. Many trailer tires have that 65 mph max speed rating whether for very small or very large trailers. The tire manufacturer has tested each tire and the speed rating is given. Often this is based on how the tire heats up with the road friction as heat is the number one reason for tire failure. I've attached an article with frequently asked questions and answers to assist.

For instance the Kenda K353 Bias Trailer Tire - 4.80-12 - Load Range B # AM10060 is only rated for speeds up to 65 mph where the other tires are rated higher. Because you are wanting to run the trailer at highway speeds, I recommend the Taskmaster 4.80R12 Radial Trailer Tire - Load Range C # TT48012C which is rated for speeds up to 81 mph. This radial tire is designed to run cooler at highway speeds so you won't overheat and have tire failure.

expert reply by: Jason S