Tires...what are you running?

[cycleguy55]

Originally Posted by fastd

Add Mickey Thompson SR to the list.

Nope. The MT S/R is not available in 295/50R15. It's available in 26X12.00R15LT (about 0.8" smaller in diameter) and 28X12.00R15LT (~1.2" taller).

Close, but no cigar. Well, at least if you're looking specifically for 295/50R15.

[PDUB]

Originally Posted by Argess

I'd like to say "I don't find the cost of Avons amusing", yet the English language is so weird sometimes. I don't find the cost of Avons amusing, but yet I can also say the price is laughable.



True, but all but braking is a matter of choice. Braking isn't because it could be required during an emergency caused by someone else. Acceleration and braking? You may have a point on the track, but public roads are not a racetrack. I'm sure we all choose to ignore that at times, but I, for one, still can drive in a spirited manner without pushing my car to its limits where the increase of risk is substantially higher.

So... for all of you who have Avons on your car, do you also have the best brake pads money can buy? Or did you get fooled and installed race pads for the street where they won't work well as they don't get hot enough.

What about the best wheel bearings? We don't want a wheel falling of while driving.

There's a lot of things that can make a car safer or more treacherous, but the most dangerous thing of all is the driver.

Anyway, we disagree, but here's some facts I recently posted in another forum and will repeat here:

Coincidentally, I recently bought a durometer…. Just for fun. This one reads rubber hardness on the Shore A scale. So I can check my tires. Softer ought to mean better grip. Unfortunately tire manufacturer’s do not seem to list a Shore rating for their tires. Oddly, many manufacturer’s of Radio Control car tires do. That’s where I got the idea. Hmmm…..



What it is useful for, is to use it on a brand new tire, and then monitor its hardnesss as it ages (and is heat cycled by driving).

Research

I tried doing some research, and here’s some things I found:

1/ According to an old document I found on the net, my BFG Radial TAs have an initial Shore number of 62

2/ From a Corvette Forum:

Mid 50s to 70ish--anything above that & things will get a bit slick, especially on the rears

3/ From a Research Paper:

During a tyre's lifetime, the rubber hardness of individual tyres may increase by up to 15 Shore A, which is equally large as new tyres may differ in hardness due to construction and material design.

4/ From the same source (my interpretation of a chart/table):

Increase in Shore number for tires made in 1990 (with a new Shore rating of 58 ) and stored for 10 years is an increase of 0.9 per year. This was for some unknown model of tire. Other brand tires, or made with newer (or older) technology, or with a different new Shore number would likely vary from this.

5/ From PitStopUSA.com:

I learned that rubber doesn’t have a set shelf life. When stored properly, tires (rubber in general) can last a very long time. Tires can degrade over time but what degrades a tire the most is exposure to heat and light. So if a tire is stored in a dark, cool place it shouldn’t show much signs of aging.

I have been told for most of my life that “Tires get old and should be replaced every five years no matter how they look and how much tread is left.” I have also been told that as a tire ages it gets harder and looses traction. These two things don’t necessarily jibe with what I learned to during my research. Confirming or dispelling what I have been told for so many years seemed relatively simple. Measure the hardness of older tires and compare them to newer tires.

I believe that old tires don’t necessarily need to be discarded just because they are old. I also think I dispelled the myth that older tires get harder as they age. If stored properly tires can have a very long service life. It is not the age of the tire itself that causes problems but extended exposure to the sun and heat that degrades it. Certainly, years of exposure to sunlight and blistering temperatures will ruin a tire and cause it to get hard and crack.

Testing

Before I start, it must be stated that Shore readings increase the colder a tire is and really ought to be measured at room temperature (somewhere I read 23 degC). So my testing doesn’t mean all that much this time of year.

At any rate, I did some testing outside (zero degC), some inside my unheated garage (7degC) and one test at room temp (about 20degC).

First, my BFGs which I bought around 1996 and still look like new due to low mileage and being stored in a dark garage, came in at 78. Even when the summer heat comes around, I doubt I’ll be anywhere close to the “new” value of 62. So they are harder than new, and that means less grip.

Interestingly, using that 0.9 per year figure, mine could be at almost 83, but perhaps lack of sunlight helped. The other source lists a max increase of 15, so that would bring mine up to 77... almost bang on 78.

The 78 number is high based on the Corvette Forum limit of about 70.

I then tested the Michelins on my Toyota, which was outside in the cold and got 62.

It just so happens I had a brand new winter tire inside in the warmth and it measured 58. I then put it outside for about 2 hours, not enough to really get it cold, but enough for the Shore number to increase to 60.

Looking at graphs of tire age vs. Shore values, the hardening of tires (the Shore number) goes up rather quickly over time and starts to level off with a total increase of about 15.

It looks rather exponential with a lot of Shore increase in the first two years. So this means a brand new BFG might have better traction than an Avon that's several years old. Of course that won't happen as the Avons probably won't last that long.

Although Alfa02 (member here) doesn’t appear to like BFGs, I do like his quote:

“…our cars were meant to (Slide) with 15" tires, not stick…”

Interesting stuff... thank you for posting!

[ront49]

Changed out my 14 year old BFG's....had no weather cracks or issues with the TA's just thought they were over due to be replaced.Went to Cooper 245 60 15" fr and 295 50 15" rear. They balanced out nicely and seem to have good handling.

[lnfletcher]

I did the same this last year with my 14yo BFGs. I went to 17" wheels and Mickey Thompson Street Comp 245/45R17 & 315/35R17
Vast improvement on handling.
Still have my 15" wheels that I may go with M/T ST with the letters turned in and buy the lettering for the billboard look.

[Tom Wells]

Argess,

Very nice, comprehensive look at rubber hardness.

Alas, after being involved in tire construction and testing for 7+ years, hardness is not the only factor in tire safety. I definitely agree it's one factor.

Another consideration, perhaps invisible from outside the tire - but not always - is internal adhesion between the various layers of rubber, and between the rubber and its reinforcing tire cord.

Occasionally there can appear a bit of a bulge, or surface irregularity that gives a clue, but often there's no change visible to the casual observer.

As you accurately point out in so many words, the chemical composition of a tire changes over time. You might say it ages. As it does, adhesion can be reduced between the components.

As aging occurs, and it often reaches significant effects around the 5 to 6 year mark, the tire becomes structurally weaker. The rate and the extent of the loss of strength is dependent on a myriad of factors such as its design, materials, original chemical composition, any trauma that may have happened over its life, temperature conditions, and probably ten or twenty other factors.

Agreed, these cars are usually lighter in relation to their tires rated load capacity so the effect of the weakening may take longer to appear. Conversely, speed, acceleration and braking forces may hasten failure, even on a lighter car.

So, as Clint once famously said "How lucky do you feel?"

I change mine every 6 years. Anything more than that is a big dice roll - maybe it adds to the thrill?

Tom

[ACHiPo]

Originally Posted by ront49

Changed out my 14 year old BFG's....had no weather cracks or issues with the TA's just thought they were over due to be replaced.Went to Cooper 245 60 15" fr and 295 50 15" rear. They balanced out nicely and seem to have good handling.

My experience as well.

[MKS427]

Tire pressures are huge as these cars are light. My buddy has BFGs on his Cobra and he had traction issues. Somehow his pressures dropped to 14 psi front and 11 psi rear and he couldn't believe how much "better" his tires had been lately. Obviously, it is not recommended to run that low and when we upped the pressure the tires were slick again.
That said, these cars are light and the tires do not work well with 30-35 psi. I run Nitto NT01s on 17" wheels @ 22 psi per Factory Five's recommendation and they work considerably better at 22 vs 30. I do not know the recommend pressures for 15" wheels/26.5" tires, but I'm guessing somewhere below 30 psi.
I have been told, with the Nitto's, you want to be scuffing to the top of the triangles on the sidewall.
All that said, the best traction additive, I've found so far, is 200 lb plus passenger. ��

[lnfletcher]

Originally Posted by Tom Wells

As aging occurs, and it often reaches significant effects around the 5 to 6 year mark, the tire becomes structurally weaker.

Tom

Taking this into account, I need to do more burnouts to wear them out faster!

[BigGuy]

Had Goodyear Eagles but after 14 years (way over due) time to change out!
Avon’ s are pricy but my issue is they do not last long. (also not available in this area). I like the look of billboards.

So Goodrich T/A’s are on and 245 60 15" fr and 295 50 15" rear.
Talked to my tire guy and 5-6 years should be max for change out.... although
I don’t track. So I was WAY overdue! Not many choices that are DOT rated.
They are a little slick at 48 degrees yesterday, but a little driving and they will work fine.

[IMLost]

Well said Mr. Wells.
It seems like this is another topic where self justification is paramount. I.E. Do i want knock offs or WANT Knock offs'? Wilwood? Not necessary for street but you WANT them, because you WANT to have them to stop your street driven car. Horsepower? How much is enough? How much is too much?
Avons, or Cooper, BFG, get your tires for your driving habits and usage spend as much or as little as you WANT to.
Then go drive the damn thing! Or polish it and go park it at a show.