Summer and racing tire storage temperature effects

[coolingchips]

There's an earlier thread here on the effect of low storage temperature on track tires. The conclusion was that the risk is in cracking of the tire. I'd love to see if someone can conclusively say that there are no permanent chemical or structural effects to the tire if it is returned to a temperature in it's elastic range with no cracking.

 

[CapriRacer]

It's been over a week since this was posted, and since no one has commented, I guess I will.

Disclosure: I am not a chemist. I'm a retired tire engineer with over 40 years working for a major tire manufacturer. I've worked along side some very knowledgeable people and have picked up a few things about the chemistry of rubber along the way. I am by no means and expert on the subject, and I would welcome anyone who is knowledgeable to correct me if I get something wrong.

I am under the impression that within the range of ambient temperatures - including arctic conditions - I think there are no permanent affects IF there is no cracking. However, I think the "no cracking" criteria is somewhat misleading. I think there could be microcracks (say at the atomic level) for some types of rubber, so while there might not be visible cracks (that is visible to the naked eye), it is possible there is still undetectable damage.

But I also think that it is possible for there to be no damage at all - and I think this is highly dependent on the type of rubber used.

 

[FeX32]

Or if kept too long. I have personal experience that when leaving winter tires over a few years they loose much of their elasticity. This likely applies to summer tires.

 

[GregLocock]

Hmm, there is a push to define a maximum age limit on tires. I am somewhat interested in this, and although one datapoint is not much help, my Michelin Pilot tires sued daily for 15 years showed no sign of cracking when the car was scrapped. On the other hand 20 year old bicycle tires are usually cracking apart.

Cheers

Greg Locock


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[FeX32]

It is in interesting and useful topic.

The tires I was referring to were top of the line sport winters. After 4 years they were noticeably less elastic. Only used during winter months.

 

[CapriRacer]

Since I seem to be the only one with any kind of background in rubber chemistry, I'll comment. Just bear in mind, I am far from an expert - just a guy who has picked up some info from people who ARE knowledgeable.

If I understand the aging of rubber in tires correctly, 2 things go on.

1) The rubber molecules get attacked by oxygen and the long chains are broken. I'm not sure why this leads to the rubber becoming stiffer and brittle.

2) The oils and waxes in the rubber matrix evaporate (is that the right word?). The waxes and oils lubricate between the rubber molecules and make the rubber more flexible. When those evaporate, the rubber becomes stiff and brittle - and since most of a tire's stiffness (that is, resistance to movement) is from the inflation pressure, the change in rubber stiffness doesn't appreciably change the amount of movement, so the rubber cracks.

And one last thought: There are different types of rubber and each has its own sensitivity to temperature and cracking. Some are very impervious, while others - not so much. Also, different formulations have different properties. It's inadvisable to compare different types of tires as there is so much variation, you can find lots of exceptions and pretty much any "rule" you might develop will be invalidated by the experience of others. A general rule would be to keep tires away from sources of cold, heat, petroleum, and ozone - if you can. Obvious, a winter tire can not be shielded from cold weather.

 

[pwildfire]

Another side note: In my experience, tires that are used regularly last much longer than those which are stored. I am not sure why this is, but having several times left tires unused for 1+ years, have found them invariably to be unusable after that, regardless of whether mounted or unmounted, pressurized or not. On the other hand, tires obviously last much longer than that when mounted on a car and used regularly. Could it be that deformation and/or temperature cycling renews the bonds in the rubber somehow, or is it more of an environmental thing like moisture is absorbed and never rejected?

 

[CapriRacer]

Once again, I am steeping in to address something I know about but am far from an expert on.

My understanding is that within the rubber matrix are antioxidants, antiozidants, and waxes (and a few other things). Flexing the rubber allows those things to move within the rubber matrix - and if I understand this correctly, there is pressure to makes things uniform, so when those things are used up or flake off of the outside, unused chemicals will migrate to take their place.

So when a tire is not flexed regularly, those chemicals can be used up on the surface and not replaced by unused chemicals within the rubber matrix - and once the damage has been done, it can not be undone.

If you are having trouble visualizing how this works, I use the analogy of spaghetti and sauce with the spaghetti as the long chain rubber molecules and the sauce (with the bits of sausage and chunks of veggies) as the stuffed within the matrix. (OK, made myself hungry!)

 

[coolingchips]

Great conversation. I had originally intended the question to address the short term effects of low temperature exposure.

 

[GregLocock]

Capriracer's explanation makes a great deal of sense, and is almost directly equivalent to how asphalt roads work. This is the explanation why our proving grounds need resurfacing so often, they simply don't get enough traffic to move the oils around.



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

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[CapriRacer]

Greg,

I never thought about roads suffering from the same malady, but it makes sense. Asphalt flexes and I can see that the asphalt itself not only absorbs anything dripped on it, but that there would be a bit of non-uniformity throughout that flexing would help distribute.

Very interesting!