Originally Posted by TB673
Do you really need a RV tire that has a speed rating over 75 MPH?
It's about design margin. You'll find most car tires are rated 100+ mph. Driving 65 on tires rated for 75 means you don't have a lot of margin for heat buildup, throw in 120 degree day in the desert southwest and you are likely outside the design spec as the tire manufacturers won't consider 120 degrees air temp to be 'normal'. Also note the spec is per air temp, not road temp. Any idea how hot new blacktop can get in the desert summer? You can no joke fry eggs on it.
If the tire is rated per ECE, the test is done at 77 degrees, if done per SAE, it's 100 degrees. So when outside temps exceed the tested to spec, your tire is subject to fail at lower speeds as they will quickly get too hot.