A quick look at almost any RV owner blog, and you will find someone saying that they drive at “xx” mph because that is the “Speed Rating” on the tire sidewall. This is definitely not a good idea and, in my opinion, is definitely unsafe.”
“Speed Symbol” on tire sidewall
Some, but not all, tires come with a “Speed Symbol” on the sidewall of their tires. This is usually found on many “P” or passenger-type tires. There are standards in Europe for the Max design operational speed.
Here is a basic chart covering tire speed in Europe:
NOTE that the various European speed numbers are “maximum” speeds and not “average” speeds. These ratings come from European standards, not U.S. DOT standards.
In the U.S., the Tire and Rim Association (TRA), Department of Transportation (DOT), and Society of Automotive Engineers (SAE, now SAE International) have specified tests for brand-new tires, such as:
A Load Range “C” tire would have a 2-hour “break-in” at 75 mph, then run 1/2 hour at 34 psi at 80 mph, then 1/2 hour at 85 mph, which is the test end. If there are no external indications of structural failure, the tire is considered to have “passed” the “high speed” test. That test tire is then scrapped and is not to be used in any additional testing.
It appears that the European “Speed Rating” letter is being interpreted as the acceptable continuous operational speed. This is NOT a proper interpretation of the various standards.
The Tire Industry Association (TIA) says this about the “Speed Symbol: “The Speed Symbol, or V in this example, indicates the maximum speed for the tire, but it is more like a performance rating that reflects the handling characteristics after it is installed on the vehicle.”
Here is a video on reading the tire sidewall information.
Bottom line:
RVs basically use three types of tires:
- Class A uses Heavy-Duty Truck-type tires.
- Class C will normally use LT-type tires, many of which carry a “Speed Rating” number.
- ST-type tires were developed and approved based on a 65 mph speed test. I would consider 65 to be the MAX speed rating for up to 30 minutes, then the tire “life” may have been “consumed.”
I almost always limit my speed in my RV or when towing my 26′ trailer to 60-65, so I can’t suggest any faster for you as being acceptable for tire life.
So, the answer to the question in the title of this post, “Can you really drive 112 mph?” is “Definitely Not.”
Roger Marble
RELATED
- What effect does speed have on tire failure?
- ST tire speed rating, and why you should stay under 65 mph
- How do you figure an ST-type tire’s maximum safe speed?
- ST-type tire speed ratings – One man’s opinion
- More on safe driving speeds, and the finite life of tires
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