Originally Posted By: JHZR2
Great insight! Can you comment on why manufacturers won't admit to having three cap plies on W and Y tires?....
On the sidewall of every tire is a statement about the tire's construction. It's required by law and takes this form:
Tread: 2 plies polyester, 2 plies steel, and one ply nylon
Sidewall: 2 plies polyester
(or whatever it is)
Since this is publicly available information, I don't think any tire manufacturer would refuse to answer a question about this.
- BUT -
Cap strips don't show up there - nor do those extra layers at the belt edges.
I would think that any question about those would trigger a defense alarm in whoever would answer those types of questions.
For example: Here's one way to word this question: "Does the Goodstone FireEagle W rated tire have 3 layers of nylon at the belt edges?"
If I were responding to that, I would wonder why the question was asked. While it may seem pretty innocuous, it's a little too specific. It also covers more than one size, so any response has to be generic enough to cover not only the past and current, and all sizes, but the future as well. I HATED having to answer those questions, because it required a lot of research that wasn't going to be reflected in the answer, and there was always the possibility that I would be wrong - that there was an exception out there somewhere.
The easy way around this would be to say "I'm sorry, but that information is considered proprietary."
And that's why I don't think you'll get that info.
Originally Posted By: JHZR2
........Also while I'm a proponent of getting the right speed rating tires due to sidewall stiffness and suspension design, it's true we don't drive legally anywhere that speed ratings can be exercised. So failure rate aside, is there a practical benefit to having more cap plies on a tire run on a pedestrian car, due to something like puncture/foreign object resistance, blowout (from an external cause) resistance, avoidance of going out of round, etc?
Just so you are aware: While the general trend is for higher speed rated tires to have stiffer sidewalls, much of a tire's handling qualities aren't affected by the things that are done for speed ratings. So it is quite possible to have a fairly sluggish, but soft riding, high speed rated tire AND a harsh riding, quick responding low speed rated tire. They aren't mutually exclusive.
On the other hand, speed ratings and aspect ratios tend to follow each other - and that really complicates trying to sort all this stuff out. I'm fortunate to have been in a position to see how this works from an engineering perspective.
So to answer your question: There are both advantages and disadvantages to having cap plies.
I already mentioned tire durability. Other advantages are impact resistance and cut through resistance in the tread area (the sidewall is largely unaffected)
The biggest disadvantage is flat spotting. Nylon is one of most flat spot prone materials used in tires - but it has this most wonderful property of shrinking when heated. So as a cap ply material, it is unusually suited to the task, except for that one annoying property.
I've often wondered why polyester or kevlar aren't used (I don't know of anyone not using nylon). Not having been involved in such research, I just don't know. I do know that kelvar has been known to shatter when compressed - and there may be similar reasons why polyester doesn't work - I just don't have any info on the subject.
And one last thought: Adding cap plies makes the tread area stiffer - and that helps a whole bunch of things - treadwear, resistance to irregular wear, handling. But it also hurts ride.
- BUT -
There are things that have much greater affect on those properties than the presence of cap plies, so don't take as a given that you'll get those kind of changes just because there is (or isn't) a cap ply.
