Going down one speed rating OK?

[cderalow]

Originally Posted By: labman
If you really wanted to save lives, you would forget the speed rating [censored] and go with traction rated tires.



of course, you'd probably be pretty hard pressed to find tires that aren't at least "A" rated when it comes to traction these days anyway.

So you point is... pointless.

 

[Quattro Pete]

Originally Posted By: labman
If you really wanted to save lives, you would forget the speed rating [censored] and go with traction rated tires.

All passenger tires are rated for traction. It's a government/NHTSA requirement.

 

[Volvohead]

Originally Posted By: labman
If you really wanted to save lives, you would forget the speed rating [censored] and go with traction rated tires.


Traction? Traction don't mean squat when the sidewall blows wide open at 70 mph.

The DOT traction and temperature ratings are unhelpful at best. A lot of crummy tires I'd never ride on carry an A traction rating.

 

[fsskier]

Does everyone only live in the desert??
I asked Leroy, a full time tow truck operator the following question: How come you are towing all those wrecks out of the ditch/median/etc off the interstate, his answer is as follows.

Right now, mostly sliding off the road in the snow.
In the summer, usually the rain.
How many wrecks do you tow every year? "Hundreds."
How many because of blowouts? "right now I don't remember any that caused the cars to lose control and have a wreck" "Of course sometimes people say they blew out, but they didn't"

Yes, there are blowouts, he finds them parked along the road waiting the truck. And, yes blowouts can cause accidents.
But, except for tippy teetery, overloaded and underinflated SUVs they are less of an issue than traction.

Earlier I mention that I had purchased several H rated tires that had nearly 0 traction in cold rain. None, Zilch, unsafe at any speed. Wheelspin in cruise on interstate upgrades. New tires, hydroplaning. Continued retesting at low speeds confirmed that after breakaway traction dropped to zero. When towing a boat
even stops at 20 mph - in the rain - could seem like ice.

Does this issue concern no one else?? I have been involved in SCCA club racing, crewed on Formula cars for years, am not a newbie to the concept of traction or handling. We constantly compared changes of less than 1 percent, now I mention losses that seem to be about %90 and nobody else is interested?

***? What rubber chemistry makes some tires so bad? What rating system failures allow these tires to have A traction ratings?
Incidentally, I am not opposed to speed ratings. Since I support a fleet of trailers, it seems that T and H rated car tires (used on our trailers) never blow out, 50 psi trailer tires blow constantly. Does the DOT testing cause car tires to exceed the quality of trailer tires?
And finally, how much wood could a wood chuck chuck?

 

[labman]

Originally Posted By: cderalow
Originally Posted By: labman
If you really wanted to save lives, you would forget the speed rating [censored] and go with traction rated tires.



of course, you'd probably be pretty hard pressed to find tires that aren't at least "A" rated when it comes to traction these days anyway.

So you point is... pointless.



Yes, but the A rated ones stink.

 

[Quattro Pete]

Originally Posted By: fsskier

Right now, mostly sliding off the road in the snow.
In the summer, usually the rain.

Is that surprising? Obviously traction in snow/wet is not as good as in the dry, regardless of tire/speed rating.

In addition, as I'm sure you know, the pavement is the most slippery right after it started raining - water mixes with dirt and oils that accumulated on the pavement. This is probably when most of the traction loss and accidents take place. Again, all tires are succeptible to this, not just the H/V-rated ones.

Quote:
What rating system failures allow these tires to have A traction ratings?

Traction is tested at some specific ambient temperature range at a government course somewhere in Texas. I'm sure it is well above freezing point - maybe Capri can provide more specific data.

 

[Volvohead]

Maybe not in Iowa, but here in the northeast, the roads are typically bad, and we see plenty of blown out tires and others that are about to blow. The roads are the worst in the winter, when tires are more prone to be underinflated. The pothole pounding and overheating kills some of them.

I honestly don't see the correlation between speed ratings and traction that some others are pressing. The speed and load ratings are indicators relating to tire failure. Traction is a performance indicator that is still subjective to operator factors. My Y rated Michelins grip like velcro in all conditions. Plenty of T rated tires have good traction, but that doesn't make them safe on the wrong vehicle.

 

[fsskier]

Rain Traction:

Yes, of course the worst traction can be at first. The tires that I will nominate as "worst rain tires ever", the Kelly Charger HR's would spin in FIFTH GEAR on a Taurus MT5. This was on the interstate on pavement (not asphalt) during an all day rain.
For the last several years I have pulled a boat up a ramp about 5 days a week, and notice that many tires are hopeless even at starting traction on wet concrete, while others are excellent.

My question remains: Should we not be more interested in rain traction (us non-desert dwellers drive in it a lot) at least as much as certification for speeds of 140 or more mph??
[censored], I spend very little time at that speed!!!
And, do not want to think about the time we spent at 125 mph with monster v8s on l950's tires that would never come close to todays S rated tires!

(OK, that could be another thread. Why would we stick our life savings into a motor, then stick on used tires that we found behind the gas station??)

 

[crinkles]

Originally Posted By: Shannow
Down here, they are supposed to install tyres rated to at least what was supplied by the OEM.

To fit lower rated tyres could expose the owner of the vehicle to unpayable insurances.

It's ludicrous, as in most of the country, the speed limit is 110km/hr tops, and 50km over the limit guarantees no licence for a long time.

So why do they even need to fit tyres rated for over 160km/hr ?



my car came with 94V tyres from the factory, tyre spec sticker says V or H is fine.

they need to spec the speed rating above any speed the car could possibly achieve.

maybe there is an additional fat safety factor in there? and maybe the robustness of the tyre is related to the speed rating and is a "more determining" factor than the speed the car coulda ctually achieve.

I have no qualms fitting H rated tyres to my car... have done so in the past. $80 vs $120 per tyre...

 

[CapriRacer]

First let me apologize. I have been deliberately provocative in order to stimulate discussion. I apparently succeeded. Plus, I am gratified to see that the conversation has turned to the realization that it is difficult to give short, concise “truths” that are universally true – not just true for a certain locale.

For example, there are certain parts of the US where speed ratings become very important – hot climates. In those areas, this is a safety issue in that the risk of a tire failure in several orders of magnitude higher than the risk it is in cold climatic areas – like Minnesota.

This is also true for traction and tire wear. There are parts of the US where the pavement adversely affects wet traction. I don’t know if this is what fsskier is experiencing or not.

But I have noticed that many tires that come on Japanese based vehicles have a higher level of traction complaints than US and European based vehicle manufacturers. I’ve discovered that all Japanese based vehicle manufacturers require traction testing to take place in Japan. I’ve also discovered that our tire engineers are sometimes bewildered when a tire they submit to a Japanese based vehicle manufacturer fails the traction requirement. I suspect the problem is the traction surface that is used in Japan.

I’ve also noticed that there appears to be a tire manufacturer / locale relationship between traction complaints. Put another way, certain tire manufacturers seem to have more traction problems in areas of the US where other tire manufacturers do not – and vice versa. I suspect that this may be the result of differences in tread compounding – things that are peculiar to one tire manufacturer over another – and how those compounds interact with the road surface. I have seen reversals of rank order of tires depending on the road surface.

A question was asked about DOT traction testing. Here’s what Tire Rack has published on the subject:

************************
Traction Grades

UTQG Traction Grades are based on the tire's straight line wet coefficient of traction as the tire skids across the specified test surfaces. The UTQG traction test does not evaluate dry braking, dry cornering, wet cornering, or high speed hydroplaning resistance.

The Traction Grade is determined by installing properly inflated test tires on the instrumented axle of a "skid trailer." The skid trailer is pulled behind a truck at a constant 40 mph over wet asphalt and wet concrete test surfaces. Its brakes are momentarily locked and the axle sensors measure the tire's coefficient of friction (braking g forces) as it slides. Since this test evaluates a sliding tire at a constant 40 mph, it places more emphasis on the tire's tread compound and less emphasis on its tread design.

In 1997, the UTQG Traction Grades were revised to provide a new category of AA for the highest performing tires in addition to the earlier A, B and C grades. Previously the A grade had been the highest available and was awarded to tires that offered wet coefficients of traction above 0.47 g on asphalt and 0.35 g on concrete. Today the grades and their traction coefficients are as follows:

Traction

Grades....Asphalt..... Concrete
AA Above 0.54 0.41
A Above 0.47 0.35
B Above 0.38 0.26
C Less Than 0.38 0.26

Unfortunately the immediate value of this change to tire buyers will be limited. Use of the AA grade will first be seen on new tires that are introduced after the standard was enacted and will then appear later on tires that have had the required wet traction all along, but were introduced when the single A was the highest available grade.

**************************************************************

Filling in some of the details: The test surfaces are in San Angelo, TX. The test requires the use of a control tire – commonly referred to as the SRTT (Standard Reference Test Tire). This is standard tire traction testing protocol as the test surface will vary – over the course of the day, from day to day, and over longer periods of time. The test results are then “corrected” based on the SRTT results. There is also a correction for the ambient temperature conditions.

They monitor the condition of the test surfaces with the SRTT by correlating the results of the repeated use of the SRTT over time to assure that the test surface is still giving consistent results. If not, it is time to repave the test surfaces.

As was asked, there are ambient temperature limitations on test, but I forget what they are. But the fact that there is a temperature correction as well as a correlation to the SRTT pretty much eliminates temperature as a variable.

BTW. to get a rating, the tire has to achieve the levels specified above on BOTH surfaces.

As Tire Rack points out, the test is more or less a test of the tread compound and not a test for the tread pattern. As speed increases, the hydroplaning resistance of the tread pattern becomes a greater and greater factor in the actual traction perceived. Some of the best traction compounds can perform poorly on tires with poor tread patterns.

But road surface also has a major effect on wet traction.

For example: Every day I travel on an Interstate highway that has been specially paved with a porous macrostructure. On a rainy day, you see the air clear of the water mist being kicked up by the tires when you enter that portion of the highway.

If you’ll do a little research on road surfaces, you’ll find studies on the wet traction coefficients of various types of surfaces. Some roads in Texas are reported to be have such low wet coefficients that they are comparable to the coefficients of ice.

But fsskier brings up an interesting question:

****************
“Should we not be more interested in rain traction (us non-desert dwellers drive in it a lot) at least as much as certification for speeds of 140 or more mph??”

*********************

I think what is trying to be expressed is a false assumption that high speed rated tires are not good for wet traction. If you’ll take a look, many V and higher tires have AA traction ratings, and at worse A ratings, where very few S and T rated tires have AA ratings, and in fact some have B traction ratings.

Needless to say, there will be some road surfaces where wet traction will be ….. ah, let’s say, less than acceptable. This has more to do with the individual tire than its speed rating. So I don’t think you have to choose between the 2 – you can have both.

BUT

The most important thing I want to get across about speed rating is that the rating is not an absolute. The actual speed capability of a tire can be quite a bit lower than the speed rating suggests. In fact, there is such a growing concern about this that momentum is gathering to rename this rating in such a way that it removes the "speed" as a number from the rating.

 

[crinkles]

Originally Posted By: CapriRacer
BUT

The most important thing I want to get across about speed rating is that the rating is not an absolute. The actual speed capability of a tire can be quite a bit lower than the speed rating suggests. In fact, there is such a growing concern about this that momentum is gathering to rename this rating in such a way that it removes the "speed" as a number from the rating.



and therefore the need to specify a speed rating MUCH greater than the car can actually achieve (my camry needs V-rated tyres, yeah right!)

maybe a "robustness rating" rather than speed rating.

 

[cderalow]

Originally Posted By: crinkles
Originally Posted By: CapriRacer
BUT

The most important thing I want to get across about speed rating is that the rating is not an absolute. The actual speed capability of a tire can be quite a bit lower than the speed rating suggests. In fact, there is such a growing concern about this that momentum is gathering to rename this rating in such a way that it removes the "speed" as a number from the rating.



and therefore the need to specify a speed rating MUCH greater than the car can actually achieve (my camry needs V-rated tyres, yeah right!)

maybe a "robustness rating" rather than speed rating.



your camry is most likely electronically limited to 120mph or so.

it can achieve those speeds.

I had an older (98) civic coupe that was electronically limited to 115, and could achieve that speed. Before I further modified it, I removed the speed limiter and was able to attain upwards of 120 (I honestly don't know how fast it went, as the speedometer stopped slightly over 120).

My current car (08 Si) is electronically limited to 136mph (and it's seen those speeds). The car is capable of faster (in fact, the 2006 Si's weren't limited, and testing of stock units has gotten people into the 150's). which is beyond the V rating of the factory all seasons, though not beyond the factory summer tires.

 

[fsskier]

Capriracer: Now there is an answer I like!!
Some tires are MUCH poorer in the rain then other tires that seem to have similar ratings, appearance, etc. And I am very interested in avoiding those tires.
Some responders (Quattro Pete) missed the point stating things like: Of course you have less traction in the rain.
Your response certainly added some light to the process used to determine these ratings, and hopefully pressure on the manufacturers to correct the worst tires.

We had a lot of rain last year, (Cedar Rapids was washed away)
and this subject has come up a lot. Local astute drivers often state that Bridgestone/Firestone seems to have many tires in the "no wet/snow traction at all even when new" category, and that seems to match nicely with the Tire Racks owners surveys.
(yes, I know, some of their tires are ok)

Do you want to tackle question number two:
IS trailer tire testing nearly as complete??

We use a lot of 205/70-14 (or close) tires on our trailers.
Clearance issues prevent us from going much larger, and we load them to the max (sadly, sometimes more)

So Far: Titan trailer tires eventually all blow out
Goodyear Marathons occasionally fail
Nanco trailer tires fail so fast we filled out the NHTSA/DOT online stuff, but they did not seem interested as long as nobody lost control!!
T and H rated car tires, blown up to 45 psi
seem to never fail.

Yes, if you make lots of road trips with a fleet of trailers you will be buying whatever you can find along the way!!

And thanks again for your last response!

 

[Quattro Pete]

Originally Posted By: fsskier

Some responders (Quattro Pete) missed the point stating things like: Of course you have less traction in the rain.

Thanks for taking my response out of context. Please go back and re-read the part that I was responding to, regarding your tow truck friend's account of what causes wrecks.

The bottom line is, just because a tire is H- or V-rated, it doesn't mean it's worse in the wet than other speed-rated tires. Hopefully Capri was able to explain it for you.


Originally Posted By: fsskier

H and V rated tires are often very poor in rain, some are just plain dangerous.


Originally Posted By: CapriRacer

Sorry, just the opposite - compared to S and T rated tires, H and V rated tires have much better wet traction - all other things being equal.

 

[CapriRacer]

Originally Posted By: fsskier

..........

Do you want to tackle question number two:
IS trailer tire testing nearly as complete??

........


I’m not exactly sure what you are getting at, but I’ll just start typing and hopefully somewhere along the way, I’ll answer your question.

ST tires:

These are tires where the size starts with the letters “ST” – which stands for “Special Trailer” - as opposed to “TR” after the size which are truck like tires which are designed specifically for semi tractor trailers. “TR” tires are typically sized for “Low Platform” trailers and the tire sizes are pretty small, but they have to carry the same loads as full size truck tires.

ST tires are typically used in light trailer applications – campers, car haulers, etc. – and while they are “sized” like passenger car tires, they use more inflation pressure and carry more load,

For example: An ST 205/75R15 Load Range D has a load carrying capacity of 2150 # at 65 psi, where a P205/75R15 Standard Load has a load carrying capacity of 1598# at 35 psi.

Here are some other statistics:

If a P205/75R15 Standard Load tire is used in a light truck or trailer application, the load carrying capacity has to be reduced by 10% to 1453# at 35 psi. For comparison an ST205/75R15 Load Range D (or C or B) has a load carrying capacity of 1480# at 35 psi.

So you may ask why aren’t these numbers exactly the same – after all, the “size” is the same! This gets into the way the load carrying capacity is calculated.

There is a basic formula that was originally introduced in the 1930’s that uses the physical dimensions of a tire (the size of the air chamber) and the inflation pressure, and then uses adjustment factors to account for different uses.

For example, there will be a factor because this is a light truck / trailer application, and another factor because the speed will be limited to 65 mph, and yet another factor because the tire is for usage on paved surfaces, etc.

By comparison, the same formula is used for aircraft tires for the airlines. What is different is that an aircraft tire is operated for a short period of time, but is subjected to very high speeds and huge impact forces – and the adjustment factors take this into account. Plus, weight and physical dimensions have to be small compared to the loads being carried. As a result, aircraft tires are physically small (compared to tires with comparable load carrying capacities) and use very high inflation pressures (up to 350 psi!).

Here’s where the problem comes in – and it is similar to the speed rating problem.

The standard test for tires is done on a 100°F room on a 67” diameter wheel at the rated load and rated inflation pressure at 50 mph for 2 hours (I think! I need to check on this to be sure, but it is something like that!). This has been the standard for decades and has served the industry well.

However, over the years, it has become evident that tires meeting this standard are not sufficient for certain conditions – in particular climates with high ambient temperatures. The problem is once you have introduced the standard, it is problematic to change it. – there is no "Undo" button.

So over time, passenger cars have gradually been using tires with higher than needed load carrying capacities – what we in the tire industry call reserve load. I can document 3 time periods where there were changes in the way tires were sized for passenger cars.

Unfortunately, this gradual up sizing did not take place in pickup trucks (and SUV’s). This was one of the lessons that came out of the Ford / Firestone situation a few years back and if you’ll notice, pickup trucks and SUV’s are now coming with tires that are larger than the minimum needed.

However, this lesson has not been transferred to trailer manufacturers – for number of reasons.

1) There are a lot of trailer manufacturers and getting them all to agree on a standard is difficult, even if they felt the pressure.

2) Most trailer manufacturers do not buy directly from the tire manufacturers, so it is difficult for the tire manufacturer to apply pressure to make this sort of change.

3) Trailer manufacturers are just not as sophisticated as motorized vehicle manufacturers are. They just don’t do much in the way of vehicle dynamics studies. It is those types of studies that result in studies involving the dynamics of tires.

4) The responsibility for tire failures on trailers falls more on the tire manufacturers shoulders than the trailer manufacturer.

5) Because a tire failure rarely injures anyone, the government regulators do not have enough clout to force anyone to do anything about it.

6) ST tires are very price sensitive.

7) Most ST tire manufacturers are not mainstream tire manufacturers.

I’m not sure how much of this is cause and how much is effect. Surely reason #6 is at least partially the cause of #7.

So, yes, there is less testing done on ST tires, but there doesn’t need to be as much. Further, the real problem seems to a number of factors.

 

[XS650]

CapriRacer,

Thanks for another educational post.

 

[Rolf]

Originally Posted By: CapriRacer
Put another way, if you operate your tires the way you described, there might be a 1 in 10,000 chance that you'll have a tire failure, but if you use an H rated tire the risk is virtually nil.


The bulk of tire failures are of owner origin:

- underinflation

- overloading

- failure to maintain (e.g., unattended sidewall damage, curb damage, potholes at high speeds)

rather than overspeed issues.