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Difference between tires with different speed rating?

xnicke (Mechanical) (OP)
15 Jan 09 7:24
Yesterday while searhing the internet for new tires to my car, I started thinking about the speed rating of the tires. I have always just bought acc. to manuf.
If a tire of same brand/modell and size has different speed rating, what in the tire construction differ? Will factors like wear, noise level and traction differ?
CapriRacer (Mechanical)
15 Jan 09 15:48
"Will factors like wear, noise level and traction differ?"

Maybe, but you should be able to determine the effect by looking at the UTQG ratings.

BTW, the noise level is more a function of the tread pattern, so in theory, the same size, etc., that should be the same between speed rating differences.

"....what in the tire construction differ?"

Basically, whether there are cap plies or not.  The following is an extremely simplisitc overview:

S rated tires generally don't have any, T rated tires generally have cap strips over the belt edges, H rated tires have a full cap ply, V and higher rated have 2 cap plies.

There are lots of variations on this.

I can see where a guy with a 4 door sedan might question the use of a V rated tires - and I tend to agree.  However, I personally don't recommend anyone use lower than an H rated tire on anything! (unless it's unavailable in the size needed.)

The short explanation for this is:

Adding a cap ply to a tire seems to disproportionally improve the tire's resistance to tire failure.  Pretty much all tire failures occur in S and T rated tires (H and higher are almost immune).
xnicke (Mechanical) (OP)
15 Jan 09 17:23
I see. That more or less what I thought. I still wonder about if there is a correlation between speed rating and rubber hardness.
Also, when comparing test done by magazines etc. the result often don't seem to be the same. To me it seems not uncommon that a tire getting a top result in one test for e.g. noise could be in mid position in the next test I read. I started to think that it might be because that they possibly tested different sizes/ratings etc.
CapriRacer (Mechanical)
16 Jan 09 8:42
".....if there is a correlation between speed rating and rubber hardness."

Ah ..... well ..........   Ya' see, hardness is not really a good way to judge the traction qualities of rubber - which is what I assume you were refering to.  The short version is that there are many variables in rubber compounding that affect traction and you can get reversals if you are using hardness as the indicator.

".... To me it seems not uncommon that a tire getting a top result in one test for e.g. noise could be in mid position in the next test I read. I started to think that it might be because that they possibly tested different sizes/ratings etc."

I am not at all sure what you are trying to say here.

If you mean that tires rated high for noise might not be rated high for some other property, then you should be aware that there are compromises to be made when designing tires.  Noise, for example, can be improved at the expense of wet traction.

But if you mean that in one test a tire is rated high and in another the tire is not rated high FOR THE SAME PROPERTY, then there are a couple of possibilities:

OE tires - that is tires supplied to the vehicle manufacturer's assembly plants - are designed to that vehicle manufacturer's specifications - and the specifications could be quite different between vehicle manufacturers.

So if you are reading about how tires perform on one new car, and find another test on a different vehicle, the tires are probably designed to different specifications.

Further, the vehicle itself greatly affect the results.  If a tire is judged to be quiet on one vehicle, it just might be that the vehicle is insulated to attenuate the particular frequency that the tires generate.  Put the same tire on a different vehicle that is insulated for a different frequency and the tires could be judged to be noisy.

That is why tires ought to be tested in the lab or in ways that limit the influence of the vehicle.

Further - tire comparisons ought to stay away from OE tires.  
TheBlacksmith (Mechanical)
16 Jan 09 8:53
I think one of the auto manufacturers specs is low cost.  Every vehicle I've ever owned had its handling, traction, and tear wear improved with quality aftermarket tires.
evelrod (Automotive)
16 Jan 09 12:55
I agree that one of the primary concerns of the OEM's is probably 'cost'.  In all instances of the cars I have purchased new, the tires have been substandard compared to quality aftermarket.  
The exception makes the rule?  Well, yes... at least for me.  My 1991 Dodge/Cummins duelly had Goodyear ten plys that lasted 100,000 miles (I'll admit that I "pushed" it a bit from 95,000 to make it).  The second set were 'equivelent' (?) Goodyears that only lasted 60,000.  Im on my third set of tires.  One size larger (235-85-R16 ten ply heavy duty) Uniroyal that have made 40k to 50k and still look "new"...One of them is starting to get some "dry cracking" on the sidewall...Sits in the sun a lot these days...Don't drive it as much as I should, anymore...Gotta look into that, soon!

CapriRacer (Mechanical)
16 Jan 09 15:26
It is a common misconception that "inexpensive" also means "low quality".

Vehicle manufacturers do indeed purchase tires at a much lower price than what you'll find at the corner tire shop.  After all, wouldn't you be able to get a huge discount if you purchased hundreds of thousands of identical tires for 3 years straight, had them delivered on a steady basis every day by the truck load to the same location?  You just can't ask for a better situation from a cost point of view.

On the other hand, that volume gives them the right to be very demanding.  Asking for specially designed tires - and require the testing to back it up.  Asking for things that an ordinary customer might not want.  And since they are going to turn around and sell the tire as a part of something bigger - and they are not going to supply a warranty on the tiret - they will do things like demand low rolling resistance, which would result in a better fuel economy figure for their vehicle, knowing that it hurts traction and/or wear - and since they're not responsible for fielding the complaints - they turn a blind eye if there are sometimes a lot of complaints!

No, it is a myth that OE tires are "cheap" and that explains the performance issues.

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