Barry's Tire Tech: New/Revised articles

I was looking at a premium tire that had an "H" speed rating but a "B" temperature rating. That seemed a bit unusual as normally I expected to see a "A" temp. rating; unless it was a "T" or lower speed rating.

I guess I still do not understanding the Temperature Test and saw your explanation below. Could you put some numbers as an example? For example if a tire had a load rating of 1,200 lbs. and a 44 psi sidewall rated max pressure then I believe the tire would be tested at 44 psi ? However, I don't understand how or why the load may vary at 88% vs. 93% of rated capacity - not clear on the difference ?

Perhaps more importantly, since one normally is running at a lower than the max sidewall pressure, say 32 - 34 psi or ~10lbs.; does that provide a margin of safety so that a "B" temp. rating is not normally a concern over the life of a tire?

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Temperature Rating Test:
  • The test is run at 88% of the rated load
  • The pressure varies according to the type of tire, but the net effect is the tire is run at 93% load for the pressure.
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And, should one generally be concerned with a "B" temp rated tire if they are being used in the Southcentral and Southwest where speed limits are 80 mph and air temps can be 100F in summer (I suspect asphalt surface temps would be much higher)?
 
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I was looking at a premium tire that had an "H" speed rating but a "B" temperature rating. That seemed a bit unusual as normally I expected to see a "A" temp. rating; unless it was a "T" or lower speed rating.

I guess I still do not understanding the Temperature Test and saw your explanation below. Could you put some numbers as an example? For example if a tire had a load rating of 1,200 lbs. and a 44 psi sidewall rated max pressure then I believe the tire would be tested at 44 psi ? However, I don't understand how or why the load may vary at 88% vs. 93% of rated capacity - not clear on the difference ?

Perhaps more importantly, since one normally is running at a lower than the max sidewall pressure, say 32 - 34 psi or ~10lbs.; does that provide a margin of safety so that a "B" temp. rating is not normally a concern over the life of a tire?

-----
Temperature Rating Test:
  • The test is run at 88% of the rated load
  • The pressure varies according to the type of tire, but the net effect is the tire is run at 93% load for the pressure.
-------
And, should one generally be concerned with a "B" temp rated tire if they are being used in the Southcentral and Southwest where speed limits are 80 mph and air temps can be 100F in summer (I suspect asphalt surface temps would be much higher)?

Cressida,

You've hit upon one of the reasons I don't like the temperature test. This is already confusing, and that test just makes things worse.

Now for some clean up: I want to apologize because I have been saying the speed rating tests were conducted at the wrong pressures. H speed rated tires are tested at 41 psi, and V and higher at 44 psi. - and it's actually more complicated than that!

Barry's Tire Tech: Speed Ratings

And here's a link to the UTQG webpage:

Barry's Tire Tech: UTQG Ratings

Allow me to clear up the load thing first.

Taking your example of a tire with a max load of 1200# with a max pressure of 44 psi.

What is the rated load? 1200#. What is the rated pressure? 35 psi (assuming a Standard Load P metric). Notice it is NOT the max pressure of 44 psi.

There would be load table associated with the tire and it would look something like this:

Pressure ....... Load Limit
35 psi...............1200#
32 psi...............1000#
29 psi............... 800#

(Note: all values made up!)

So if I test at 88% of the rated load, that's 1056#.

If the test pressure is 32 psi, then I am testing at effectively 105.6% load.

That's why the confusion on the load. The test is NOT conducted at the rated pressure, but is conducted at some percent of the rated load. which is different than the load limit for the given pressure. This happens at lot in tire testing.

So now let's look at the 2 tests:

.................Temperature ......... Speed
Room Temp.....95F..................77F
Effective Load...93%..............109%
B Temp = 100 mph minimum
A Temp = 115 mph minimum
H speed = 130 mph minimum

Notice that the tests are challenging in different ways, so it's not clear how a tire would perform in both tests.

My guess is that you've encountered a tire that barely passes an H rating, and doesn't pass the A Temp, so it is B Temp. Normally H rated tires will get into the A rating.

So what about driving in the southwest and south central?

I think this has more to do with the construction - specifically cap plies. H speed rated tires generally have cap plies, but you've encountered a tire that I wonder if it has full cap plies. It might be the B Temp rating is because it only has cap strips over the belt edges.

The states of interest are AZ, CA, NV, TX, and FL. There is data to support the idea that S and T rated tires are prone to failure in these states - less so in neighboring states.

What is MO? Not one of those 5. It might be OK.
 
Tire pressure does drastically affect what the amount of load is that a tire can handle. And this is even more critical on hot days.

I remember when I worked for a cement company back in the '70s and they sent out a flatbed that just had Duallys on the back and the day's temperature was 99 Fahrenheit. That truck ended up blowing out three out of the four back tires. They sent me out with an identical truck but before I got in the truck they told me to overfill the tires by 15 lb above rated. Then they said that I should go to where the truck had broke down and that their mechanic would be following me and have tires for the truck that broke down. We transferred the load of rebar by hand from the broken down truck to my truck. The amount of rebar was approximately twice the capacity of the truck as far as weight goes.

When I started driving away after a while it felt like my back tires were traveling on ice because I could feel the truck sliding sideways somewhat as I was going down the highway. The rubber on them was heating up so badly that they were actually slippery. Every time I realize that that was going on I pulled over and waited 15 minutes for the tires to cool down before going again. I continued on the trip like this and after the sun went down the tires no longer required cool down timeouts.

This was a real Fly by Night kind of quality cement company in Andover Ohio. Back then, Vehicles did not require inspection in Ohio and the maintenance on these vehicles was terrible.

But any how one of the things that stood out about this experience is that the first truck did not have the tires inflated to maximum pressure or even a little over when they were handling an extremely heavy load. And the tires ended up failing. Apparently as soon as one field two others quickly followed.
 
I really like your articles, keep them coming!

Why is a round contract patch associated with low quality tires?
 
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