Some facts about tires

[rob_gendreau]

You might want to take a look at the temperature of the tire casing itself.

Our expert (thanks!) can perhaps tell us, but from experience on the track I expect that seeing high temps is gonna be an early warning of failure. So even if you slowed down, but had a higher than recommended pressure, you might still be getting too much flex in the tire, and that would show up as heat in the carcass, and you'd know you were in trouble.

And the heat cycling of the tires does affect their performance. Watch a F1 race and that's big part of what they talk about, getting them up to temp. But they only have so many cycles in them.

The problem of an undersized spare is interesting; anyone look at the doughnuts that come with some relatively heavy vehicles, like SUVs, to see what the specs are? I imagine that the limitation on how far you should drive on them is related to this.

[Viejo]

So even if you slowed down, but had a higher than recommended pressure, you might still be getting too much flex in the tire, and that would show up as heat in the carcass, and you'd know you were in trouble.

I was under the impression that it was LOW pressure that caused excessive sidewall flex and heat build up.

[Pschitt]

You're absolutely right Rob, temperature is a crucial indication of dynamic condition of a tire. But without a dedicated temp meter and thorough knowledge of tires, it's quite impossible to evaluate the temp and where is the limit. So it's not a criterion indicated for the public...
Contrariwise, it's systematically used in car racing, not only from tire casing but also from thread surface, to indicate how the tire is runing on the road, to maximize its effectiveness by adjusting alignment, toe, camber, pressure, etc...

I was under the impression that it was LOW pressure that caused excessive sidewall flex and heat build up.

That's right Viejo.

[rob_gendreau]

I never got good enough managing my rubber in autocross to gain as much advantage as others, but it was interesting to use a pyrometer and keep detailed records of performance, temps, pressures, etc. You learn a lot, and you can detect differences. Managing the tires was often the differences between the winners and the also-rans.

And at least it got me in the habit of constantly checking my tires.

On another note, what about longevity?

I was recently with a friend who has a Class A. We were all over him to get new tires, since they had visible cracking on the exterior. But some tires didn't and were of 2005 vintage. We couldn't convince him to get those replaced.

When do you replace due to age?

[JoeH]

Originally Posted by rob_gendreau

I never got good enough managing my rubber in autocross to gain as much advantage as others, but it was interesting to use a pyrometer and keep detailed records of performance, temps, pressures, etc. You learn a lot, and you can detect differences. Managing the tires was often the differences between the winners and the also-rans.

And at least it got me in the habit of constantly checking my tires.

On another note, what about longevity?

I was recently with a friend who has a Class A. We were all over him to get new tires, since they had visible cracking on the exterior. But some tires didn't and were of 2005 vintage. We couldn't convince him to get those replaced.

When do you replace due to age?

Most reputable tire shops won't touch those tires if they need repair. Especially in the dry, arid southwest. You can't always see the damage with dry rot. It's not worth the risk to save a few bucks.

[Pschitt]

Originally Posted by rob_gendreau

When do you replace due to age?

Main problems due to age result from exposing to ultra-violet rays that alter the consistency of the rubber in surface. This is what causes cracks often observed on old tires. These cracks are not dangerous in themselves, at least as long as they remain superficial. It's when they join the tire casing (steel carcass), allowing water to infiltrate and thus rust to attack the steel of casing, that the risk appears. You should then replace the tires without delay since rust can cause collapse of the casing in a few weeks only. Problem is the same if you hurt the tire when offroading...
A good way to prevent from cracks is to protect tires from direct sun rays when not driving.