Speed rating importance

[IndyIan]

Originally Posted By: CapriRacer
Originally Posted By: IndyIan
Any data for that? .......


There is the widely referenced Ford/Firestone situations a few years back. Those tires passed all the tests, and yet were deemed *unsafe*. That's because the problem was in the durability, which is not something that is directly measureable in short duration tests.

Originally Posted By: IndyIan
...... I can't see how in the OP's case, even driving around with the full cargo load, that the tire is likely to fail driving at 15 over the speed limit anywhere in the US? If so, why have testing and ratings at all? .........


Because they are an INDICATOR. Tires that do well on these tests are better than tires that do poorly. Ergo, an H speed rated tire is less likely to fail than a T rated tire.

Originally Posted By: IndyIan
....... If you are driving at 60% of rated speed with 60% of rated load, you would hope you are well out of the testing tolerance range... If not then whomever designed the testing needs to get sued out of the business...


It doesn't quite work like that. The testing is conducted in a lab under ideal conditions, where the real world can have all kinds of strange circumstances that are eliminated by the lab environment.

Plus, we are talking percentages here. If I take a tire that barely passes the test, it will have a failure rate of .... Oh, say 1% (not the true value!) If the tire is improved 10% (as measured on that test), the failure rate drops to - say - 0.1% (again, not the true value). So even operating a tire at only 60% of its rated value does not yield a non-zero failure rate - just an extremely small one!

So what would you estimate the absolute risk in 50k miles, for a T speed rated tire run at say my 60% load, 60% speed scenario scenario to have an internal failure? What would be the risk for an H rated tire in the same conditions?
I'd guess the difference in risk between the speed ratings, is a minute fraction of the risk of getting a flat from road debris or user error like not checking pressure often enough, and tire failure overall is a much smaller risk than other factors like weather or other drivers.

 

[CapriRacer]

Originally Posted By: IndyIan
Originally Posted By: CapriRacer
Originally Posted By: IndyIan
Any data for that? .......


There is the widely referenced Ford/Firestone situations a few years back. Those tires passed all the tests, and yet were deemed *unsafe*. That's because the problem was in the durability, which is not something that is directly measureable in short duration tests.

Originally Posted By: IndyIan
...... I can't see how in the OP's case, even driving around with the full cargo load, that the tire is likely to fail driving at 15 over the speed limit anywhere in the US? If so, why have testing and ratings at all? .........


Because they are an INDICATOR. Tires that do well on these tests are better than tires that do poorly. Ergo, an H speed rated tire is less likely to fail than a T rated tire.

Originally Posted By: IndyIan
....... If you are driving at 60% of rated speed with 60% of rated load, you would hope you are well out of the testing tolerance range... If not then whomever designed the testing needs to get sued out of the business...


It doesn't quite work like that. The testing is conducted in a lab under ideal conditions, where the real world can have all kinds of strange circumstances that are eliminated by the lab environment.

Plus, we are talking percentages here. If I take a tire that barely passes the test, it will have a failure rate of .... Oh, say 1% (not the true value!) If the tire is improved 10% (as measured on that test), the failure rate drops to - say - 0.1% (again, not the true value). So even operating a tire at only 60% of its rated value does not yield a non-zero failure rate - just an extremely small one!

So what would you estimate the absolute risk in 50k miles, for a T speed rated tire run at say my 60% load, 60% speed scenario scenario to have an internal failure? What would be the risk for an H rated tire in the same conditions?
I'd guess the difference in risk between the speed ratings, is a minute fraction of the risk of getting a flat from road debris or user error like not checking pressure often enough, and tire failure overall is a much smaller risk than other factors like weather or other drivers.


Being very careful to parse this out, but the risk of a structural failure due to something other than a road hazard, for a T speed rated tire operated at 60% of the rated load and 60% of the rated speed is currently on the order of one part per million. Please note, there are probably some tire brands that would be an order of magnitude higher, but those would be averaged against the rest of the manufacturers.

Also please note that this value is considerably lower than it was in the Ford/Firestone era 16 years ago. During that time frame, I'd estimate the overall combined failure rate for all manufacturers for the conditions listed above to be about 0.01% - or about 100 parts per million.

And if you want to got back further, the failure rate would be even higher.

Now for an H rated tire, the failure rate is on the order to 50 times better regardless of the time frame - except to say that many tire manufacturers have adopted H rated constructions for their S and T rate tires nowadays, and that is heavily impacting the current failure rate.

And just to put this all in perspective, even back 16 years ago, tires were not a major factor in automobile rated fatalities - which is why NHTSA wasn't paying much attention to tire failure rates back then!

Also to keep this in perspective, it is estimated that there are about 900 million tires on the road in the US. That means that even a failure rate of 1 part per million means 900 failures!

 

[dtownfb]

Originally Posted By: geekster
Wife ran over some screws in our neighborhood, all new construction, and we ended up having to replace the tires on the car yesterday. Car is a 15' Rogue Select and comes with 225/60 17 H tire from OEM. Had some Firestone Destination LE2 installed and they are in a T rating. Is this anything to be concerned about? My gut tells me no, but with a kid in the backseat I wonder.


Geekster, double check your owner's manual but it looks like the 2015 Nissan Rogue Select is spec for either T or H rated tires. This is why there were no red flags when you had the new tires installed. My 2006 Camry is the same way, T or H rated is fine. I would not be concerned at all with T rated tires. The biggest difference I saw between the T and H tires is the H-rated tires rode a tad bit stiffer.

As far as which is better, truthfully both will get the job done without any drama. We are talking about a cross-over SUV with limited power and athleticism. The Firestone is a nice tire that will serve you well.

Good luck.

 

[IndyIan]

Thanks for giving us some numbers to assess the risks with, your knowledge here is a great resource!

 

[Cressida]

Originally Posted By: CapriRacer

Now for an H rated tire, the failure rate is on the order to 50 times better regardless of the time frame - except to say that many tire manufacturers have adopted H rated constructions for their S and T rate tires nowadays, and that is heavily impacting the current failure rate.

And just to put this all in perspective, even back 16 years ago, tires were not a major factor in automobile rated fatalities - which is why NHTSA wasn't paying much attention to tire failure rates back then!

Also to keep this in perspective, it is estimated that there are about 900 million tires on the road in the US. That means that even a failure rate of 1 part per million means 900 failures!


1. Is there any external markings or descriptions on the tire sidewalls that the consumer can see that could help to identify those manufactures who may have adopted the advanced construction that might normally be found in the "H" rated tires?

2. I would guess the failure rate of the tires used in the over-the-road trucking industry might be much higher than the numbers mentioned? One sees so many of the tread sections "alligators" in and along the interstate roadways. It would seem that these truck tires put the public at risk since those tread sections can be pretty large. Maybe they don't call that a "failure" but I would hate to be near a truck when one of those treads fly off their tires as it could ruin your day.

 

[krzyss]

ply count is on the sidewall, duh.

Krzys

 

[FranklinJL]

Dude I think your ok, your driving a Rouge..that's a nissan right? From experience, unless your going to be driving over 150 mph alot, or tracking the car, a middle priced economy tire will fit most people's needs

 

[CapriRacer]

Originally Posted By: Cressida
1. Is there any external markings or descriptions on the tire sidewalls that the consumer can see that could help to identify those manufactures who may have adopted the advanced construction that might normally be found in the "H" rated tires? ......


Yes, the sidewall will have the construction - and what you are looking for is a cap ply under *Tread*. It will be listed as nylon or polyamide (which is the name for the family of synthetic fibers that includes nylon, kelvar, etc.)

Originally Posted By: Cressida
........ 2. I would guess the failure rate of the tires used in the over-the-road trucking industry might be much higher than the numbers mentioned? One sees so many of the tread sections "alligators" in and along the interstate roadways. It would seem that these truck tires put the public at risk since those tread sections can be pretty large. Maybe they don't call that a "failure" but I would hate to be near a truck when one of those treads fly off their tires as it could ruin your day.


Most of those *gators* have been retreaded more than once. I don't think we can count those types of failure in the same way we do car tires. Plus, those *gators* include road hazard failures. The problem is that many of them are from trailer positions and the driver may not sense the impending failure and it doesn't get noticed until after those pieces fly!

And, Yes, I would recommend that people pass trucks and not hang around the tires very long when doing it. It makes me very nervous to watch a car drive S-L-O-W-L-Y by a truck.

 

[Jarlaxle]

I suspect most "gators" are from tires run nearly or totally flat at highway speeds.

 

[Cressida]

Originally Posted By: krzyss
ply count is on the sidewall
Krzys

Indeed it is - and please keep you duh to yourself. However, one complicating factor for me is that some tires may include an edge ply and this will not be listed on the sidewall. For example an "S" rated tire will not have any cap ply while a T rated may get an edge ply. And in this case the sidewall will read the same with no mention of a cap ply.

Along this same discussion, I noted a new "H" rated Douglas tire and the sidewall only shows the "2 steel belts and 1 poly belt" for the tread. (no ply is listed)

It makes me wonder how a lower positioned tire like the Douglas achieves this H rating while examples from all of the major manufacturers (that I've seen in the same size) list a cap ply for their H tires? Seems a bit strange...

 

[CapriRacer]

Originally Posted By: Cressida
Originally Posted By: krzyss
ply count is on the sidewall
Krzys

Indeed it is - and please keep you duh to yourself. However, one complicating factor for me is that some tires may include an edge ply and this will not be listed on the sidewall. For example an "S" rated tire will not have any cap ply while a T rated may get an edge ply. And in this case the sidewall will read the same with no mention of a cap ply.

Along this same discussion, I noted a new "H" rated Douglas tire and the sidewall only shows the "2 steel belts and 1 poly belt" for the tread. (no ply is listed)

It makes me wonder how a lower positioned tire like the Douglas achieves this H rating while examples from all of the major manufacturers (that I've seen in the same size) list a cap ply for their H tires? Seems a bit strange...


First, cap strips - what you called an edge ply - aren't as good as a full cap ply, but they are better than nothing. On a scale of one to 10 where 10 is a cap ply, a zero is nothing at all, cap strips are a 3.

Second, it is possible to get even a non-cap ply tire to pass an H rating - but it is difficult. Cap strips make it easier, but the majority of manufacturers use a full cap ply. I'm guessing that Goodyear feels that the Douglas tire doesn't need a cap ply because it is an economy line and WalMart is solely responsible for returns. (Pretty poor attitude IMHO!)

 

[Hokiefyd]

Originally Posted By: Cressida
Along this same discussion, I noted a new "H" rated Douglas tire and the sidewall only shows the "2 steel belts and 1 poly belt" for the tread. (no ply is listed)


Are you sure about that? So, the tread plies indicate one polyester belt and two steel belts, and the sidewall plies indicate just one polyester belt?

I will, again, summarize a comment that I read many years ago on an engineering forum: tire speed ratings are as much about a tire's market placement than anything else. They don't speed test tires, note the speed at which they fail, and then print a speed rating on them. There can be some very well-made tires that come with a T rating simply because the manufacturer doesn't intend for that tire to be cross-shopped with more performance-oriented tires in its portfolio. And, if the Douglas example above is accurate, there are perhaps some not-so-good tires out there where the manufacturer is trying to sell a tire in the highest category it can while saving as much as possible in the manufacture of the tire with lesser quality (or fewer) materials.

 

[Cressida]

Originally Posted By: Hokiefyd
Originally Posted By: Cressida
Along this same discussion, I noted a new "H" rated Douglas tire and the sidewall only shows the "2 steel belts and 1 poly belt" for the tread. (no ply is listed)


Are you sure about that? So, the tread plies indicate one polyester belt and two steel belts, and the sidewall plies indicate just one polyester belt?


Yes I'm sure - and I was surprized. I was in a Wal-mart and looked at some of the Douglas tires they had out on the floor for display over the weekend.

I suspect you are correct it's probably about the marketing aspect. Nevertheless, you would think this could backfire if they are pushing the envelope to get that H rating. I guess they figure it's good enough to not fail catastrophically and if the H rating gets a few more units out the door that's all that matters. If one of these tires should fail and someone gets hurt, the lawyers may circle around the point about why they were marketing the tire with an H rating if indeed the construction is different than many other examples with the same rating. It doesn't sound like a good business decision from my prospective.

I also was in a Pep-Boys and found it interesting that many of the no-name (those strange name private label examples) tires they had on display were H rated and included the additional nylon cap ply listing on the sidewall. This was even in a 14" size tire and you don't find many of the major names offering anything in size 14" H rating anymore.

It has to be getting harder for the consumer to distinguish between quality as they all look pretty good on the show room floor. And, we have to somewhat guess what materials, details and controls were, or were not used, in making up these private label tires. For example, my eye was drawn to a really nice looking tire in Pep-Boys and then I looked at the name. I had never heard of it before and couldn't tell you what that name was today if my life depended on it.

 

[Hokiefyd]

Originally Posted By: Cressida
I also was in a Pep-Boys and found it interesting that many of the no-name (those strange name private label examples) tires they had on display were H rated and included the additional nylon cap ply listing on the sidewall. This was even in a 14" size tire and you don't find many of the major names offering anything in size 14" H rating anymore.


I think this supports the argument that the speed rating, while it certainly has to be backed up by the physical construction of the tire, has a lot to do with market placement. The smaller and/or house brands often do have at least an H rating on nearly everything they sell. They have a relatively small product portfolio and have to reach as many vehicle applications as they can with the few tire lines they sell. Michelin or Goodyear, in comparison, have many different product lines. You can probably find two or three T-rated tires in any given size, plus a few H-rated tires, etc. They have a lot of product to offer, and can label their tires accordingly.

The speed rating of a tire is, as I understand it, decided LONG before a sample is put on the testing equipment. They know the product placement in the market, they engineer it to meet that criteria, and they test it to affirm that it has met the standard. Douglas has apparently tested their tire and has certified that it meets the performance criteria to have the H speed rating.

Another oddity -- most H-rated tires (and above) have an A rating for temperature. But not all. I've seen a few B-rated tires for temperature that also have an H speed rating. And you've apparently seen at least one H-rated tire without an additional cap ply. All the more reason, in my opinion, to not rely on the speed rating alone as a go/no-go gauge for any one tire. Consider everything you know about the tire (including what little they give you on construction details, traction and temperature grades, speed rating, load index, brand reputation, etc), and make your decision using all of those factors.