Tire Speed Rating Question
I'm posting this here because the speed rating of a tire seems to me to cross all lines/types of vehicles. Reading up on warranty issues/questions just now, I came across the following language ...
Forum Discussion
pronstar wrote:Francesca Knowles wrote:
Someone please correct me if I'm wrong, but the way I understand that "increase the air pressure for higher speed" thing is that it refers to recommended pressure for the load as a baseline.
Taking as an example the first tire in the chart below, if installed in a position carrying 1530 pounds of weight, 40 pounds of pressure is "correct". But running it at its 50 pound maximum would allow for the higher speed.
I interpret that to mean that if one's running it at 50 pounds already, one's good for the higher speed....is that correct?
You are absolutely correct.
The "general consensus" for many posters on RV.net is that all trailer tires should always be maxed-out for psi, but in reality I believe they should have their pressures set according to load, as the MFR recommends, just as we do with any other tire.
The key thing is the Load Range letter. I have a utility trailer that rides on "185/80-13D-ST" tires with a load range of D. There is no load range D listed on the above chart for that size tire. But the specs from the tire manufacturer tell me that I can haul 1725 (for a total of 3450 lbs) lbs when the tire is inflated to 65 psi and that is the maximum for the tire. And that allows me a maximum speed of 65 mph. Load Range D indicated that the tire has a 8 ply rating. Load Range C indicated that it has a 6 ply rating. The tire will run cooler when running its maximum rated PSI, not matter how much weight it is carrying, provided it is no overweight. The reason we run motorhome tires using the tire inflation charts is for a better ride. A trailer with ST tires does not require a softer ride.
Special Trailer (ST) Service Tires
Special Trailer Service tires are often available in multiple load ranges. The appropriate load range is identified immediately following the size's rim diameter in manufacturers descriptions.
ST-Metric sized special trailer service tires will be branded with their load range (Load Range D or LRD) on their sidewalls and list their appropriate load range letter in their descriptions as ST205/75R15 LRD.
