Originally Posted By: CapriRacer
Originally Posted By: y_p_w
Originally Posted By: CapriRacer
Let's put it like this:
There are tire experts testifying in court that the construction of an H rated tire prevents tread separations.
Comments?
Duh. Full nylon cap plies typically start with H speed-rated tires. Supposedly resists tread separation in case of blowout and don't they also help tires run cooler?
What they really do is 2 fold:
1) They provide constriction to reduce circumferential growth due to centriugal forces.
2) They add structure to reduced the standing wave that gets generated. I think it is here where the "cooler running" part comes in, but I think that is not a primary effect, it's a result of something else.
As alluded to by rpn453, moderate speeds and proper inflation pressure help REDUCE the probability of a tread separation - and as Audi Junkie said, temperature plays a role here.
(As a side note - I try to be very precise in my language when I talk about tire failures - and the term "blowout" is used when the tire loses air rapidly, which is quite different than the common "belt leaving belt" separation. Most "belt leaving belt" separations - commonly referred to as "tread" separations" - do not result from - or result in - a loss of inflation pressure.)
But allow me to throw some things on the table for discussion.
1) We know that the test for a speed rating is done in a 70F temperature room, and the tire has to remain intact for one hour at the rated load and rated pressure at the speed indicated.
2) There is a study (I'll have to dig this out!) that shows that if the test is done at a lower inflation pressure and a correspondingly lower load, the tire will fail as much as 2 steps lower. In other words, a tire rated for a "S" rating (112 mph could actually only be capable of a "Q" rating (99 mph).
3) There is also a study somewhere that shows that temperature has an effect on the speed rating - again a 2 step drop was indicated. So while this might not be important if you live in PA, the folks in AZ better pay attention.
3) And a 3rd study shows that tire age causes speed rating degradation - again as much as 2 steps (which how I remember all this) Again, this is more important in hot weather states.
So while I am sure that you can't actually get a drop of 6 steps, it is certainly is reasonable to assume that it is a significant drop. Just a reminder - the difference between an "S" rating (112 mph) and an "L" rating (75 mph) is only 6 steps.
Given that belt overlays (commonly referred to as "cap plies") sigificantly reduce the failure rate of tires - and that a belt overlay is very nearly required to pass an H speed rating, I think it is just good sense to use H speed rated tires at a minimum.
OK, I'm sure there's a lot to discuss in this post .......
I did get it correct about the nylon cap, right?
Also - would the effective speed-rating degradation have a linear contribution from those factors? I'm thinking maybe if all three of those factors are in play, maybe the total contribution is maybe an effective 3 or 4 step drop and not 6?
I know in my field sometimes we test with two or three factors together that would each result in a particular degredation in performance, but the combined degradation isn't necessarily linearly cumulative when all the factors are present at the same time.
