Speed Ratings of ST-Type Special Trailer Tires

Question:

Currently on my Rockwood 1640 are installed 12inch rims with a ST145R12 tire. I recently found out the speed limit on them is 65mph. I want to go to a 13inch tire to eliminate that restrictions. The bolt pattern is 5 x 4.5. Can you recommend a tire/rim that wouldnt be much larger in size that would fit my hubs? I know Ill have to buy new rims along with the tires and Im willing to do that. My last speed rated tire failed and destroyed the wheel well of my trailer. Im trying not to repeat that episode.

asked by: Greg B

Expert Reply:

Most special trailer-type tires have a maximum speed rating of 65-mph but some tires in certain sizes can have speed ratings as high as 81 mph, which is classified as an M speed rating. If not specifically labelled for a higher speed rating, presume the trailer tires carry a maximum speed rating of 65-mph.

Changing your trailer's ST145R12 tires to the 13-inch size, such as Karrier ST175/80R13 Radial # AM10210, can allow safe travel at higher speeds since this tire is M rated for speed, but changing to a higher-load-range-rated tire will not increase your trailer's weight carrying capacity (but it will increase your safety margin). You want to be sure you have enough clearance for the larger tire in your wheel wells so that the suspension's normal travel does not cause contact.

The most important things to keep in mind with any trailer tire are to maintain the correct COLD psi pressure as noted right on the sidewall; observe the tire's speed rating; and to operate it within its weight capacity, or 'load range'.

Please refer to the linked article for more helpful information on trailer tires.

expert reply by: Adam R