Originally Posted By: Astro14
I recommend reading here:
http://www.barrystiretech.com/speedratings.html
Key point: ability of tire to handle speed is often far below the speed rating. Tire failures occur most often in S and T rated tires.
Not so fast...
Member Capriracer, the author or that article, has clarified here what he means when he says this:
Quote:
To further complicate matters: Almost all tire failures occur in S and T rated tires. Hardly any occur in H and higher speed rated tires.
I recommend that everyone use a minimum of an "H" speed rating.
He said in another thread that he recommends H and above because they generally allways have a cap ply that strengthens the tire. But, tires below H can have a cap ply, too, if they're good quality. He has said he just says H or above to simplify his recommendation, and what he's really recommending is the cap ply.
My T-rated Hankook H727s, for example, do have a cap ply. It's noted in the construction specs on the sidewall
Here's exactly what he said in another thread(emphasis added by me):
http://www.bobistheoilguy.com/forums/ubbthreads.php/topics/2774714/1
Originally Posted By: CapriRacer
For practical purposes, tires have to have a cap ply to get an H speed rating. Needless to say, higher speeds require AT LEAST one cap ply.
- and it gets a little complicated here, so bare with me:
S and T rated tires may or may not have cap plies - but the presence of a cap ply is sometimes needed in order to pass lower speed rated tests - particularly for larger tire sizes. (I'm not talking rim diameter, here.)
Some tire manufacturers will put cap plies on S and T rated - even in small tire sizes. Good for them.
Because I want to make a simple to remember recommendation, I use the shortcut to H speed rating, but the truth is that a cap ply is what I am driving at.
Weight? Cap plies hardly weigh anything, so you can't go by that.
If you want to know if a particular tire has a cap ply - ask the manufacturer!! It's required by law on the sidewall of the tire so it's no secret.
Here's even more:
Originally Posted By: CapriRacer
And allow me to address the issue of S and T rated tires failing at speeds below 75 mph:
I think there is a bit of confusion. I am NOT saying the tires are failing due to the speed. I am saying that tires are failing in spite of their being used at speeds well below the rated speed.
I am sure everyone is aware that rubber deteriorates over time. That's the reason why there are warnings about old tires. Included in this is the issue about the stresses that tires expreience - how underinflation and over-loading contribute to tire failures.
But that's stating things in "black and white" terms. This is decidedly about shades of gray. The percenbtage of tires that fail is pretty small - but it is measureable.
What is going on is that the edges of the steel belts experience a lot of stress and that's where a tire failure can start. By putting on a cap ply, the belt edges is not as subjected to as much centrifugal force, plus the cap ply acts like a bandage to keep even failed belt edges from getting worse.
And that's why I recommend H speed rated tires at a minimum.
