Originally Posted By: Jason Adcock
Originally Posted By: CapriRacer
S rated tires generally have no tread area reinforcement.
Does a lot of this depend on size?
The 225/60R16 Michelin X Radials I purchased a few years ago had no fewer than 5 tread plies. 2 polyester, 2 steel, and 1 polyamide. Sidewall was the 2 polyester plies. And their service description was 97S.
Most S-rated tires have only 3 tread plies -- 2 steel and 1 polyester. But those 225/60R16 Michelins seemed to be exceptionally sturdy tires.
This can get real complicated.
Generally, there are only so many combinations of ply material available in a tire factory. Every tire has to use what is available. If you think of a tire as a pressure vessel, then the larger the perimeter, the stronger the outer surface has to be - ergo, more ply material.
There are various ways of achieving more ply material:
1) More end count - there is an upper limit where there is too much density and the rubber doesn't penetrate very well. There is also a lower limit where it is difficult to process. For example, the factory might have 21, 23, and 25 ends per inch available.
2) Use heavier cord - the technical term is denier, a measure of the weight for a given length. For example: polyester could come in 1000/2 (2 strands of 1000 denier), 1500/2, 1000/3, and 1500/3. Obviously these are quantum jumps, and one way to have smaller increments is to use different end counts.
3) Use more plies.
So there will be a variety of distinct combinations. The trick is to provide enough variety so that no tire made is grossly over strength and there is a reasonable transitional between single ply and 2 ply tires - strengthwise.
And there doesn't appear to be any particular advantage to using more ply material than is minimally necessary.
It turns out that if you do this correctly, the transition point is somewhere about a 215 or 225 section width - and virtually every tire manufacturer makes the transition in this area.
OK, so what about cap plies? As I said, there are some tire experts testifying in court that cap plies PREVENT belt leaving belt separations - NOT TRUE!!
However, the use of a cap ply really does slow them down. Based on a couple of different observations, I think this can be attributed mostly to the dramatic increase in speed capability a full cap ply offers.
Many tire manufactures have adopted H rated constructions in their lower speed rated tires in an attempt to counter those arguments. Interestingly, this move by the tire manufacturers is in effect doing what this thread is all about!!
On a personal note, I've noticed a decided move by vehicle manufacturers to higher speed ratings. So do they agree with me that H rated tires are the minimum accepotable speed rating?
I also think the courts are strongly signaling that tires must have cap plies. I think it would be best if this was made a legal requirement. That would render this discussion moot!
But unless that happens, the issue is going to be taken out of our hands. All S speed rated tires will be built to H speed rated constructions whether we like it or not. And, of course, we will all have to pay for the privledge!
