Cracks in sidewall of tyre 1

[patprimmer]

In a post I read today in a thread in this forum I saw mention of sidewall cracks in the rubber. This got me thinking about similar but more critical situations.

I have seen some run drag slicks with cracks in the rubber near the bead and parallel to the bead. These tyres had some use but still had plenty of rubber left on the wear surface.

My uninformed opinion is that the rubber in a very thin racing sidewall is contributing very little to strength and so long as no bulges or distortion is evident, the carcase is not significantly compromised for strength and therefore from that point of view is safe to use.

I also have the opinion that if the sidewall is cracked, the rubber will most likely have hardened with age and may well have traction issues due to reduced friction.

Further, hardened rubber and cracked sidewalls may well have various influences on the deflection of the sidewalls during initial acceleration and this might hurt traction and also introduce tyre shake.

As all of this is based on assumption or intuition and it is a major safety issue, I would very much appreciate comment from someone with real data. Capriracer is one who's opinion I would particularly appreciate.

Also, is the age that causes the formation of cracks likely to reduce the bond between the rubber and the fabric or between various layers of rubber.

A further issue is that sometimes a tyre is performing VERY well but has visible cracks. We are then reluctant to change tyres that are hooking up, run straight and do not shake on a particular car, but I am also reluctant to run tyres that have a compromise to their structural integrty.

Regards
Pat
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[evelrod]

Pat, the "cracks" that I spoke of are mostly superficial and do not impact safety to any great extent...At least that is what I am told by my sponsor, a wheel and tire company.

Have a peek at "The Worlds Fastest Indian" for a 'fun' look and "cracked racing tires"...I guess you need to be from NZ to fully appreciate just how crazy going 200 mph on a set of tires that you filled in the cracks with shoe polish appears to the rest of us!!!

Rod

 

[patprimmer]

Rod

I guess I am asking if your sponsor is correct and if the racing application is different to your truck in that regard and when it stops being superficial. My feeling is that so long as the sidewall holds it's shape, structural integrity is OK.

I did see the Worlds Fastest Indian and I liked that line along with a few others. I did attribute some parts of the based on a true story to poetic licence and loose interpretation of based.

Regards
Pat
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[CapriRacer]

Pat,

Indeed! Racing tires are different than street tires. Most racing tires are built very thinly - no extras!

In the case of sidewalls, street tires have an extra layer of .... ah ..... well, let's just call it rubber. This is to provide protection for the cords. For practical purposes, it could be made out of anything - and for practical purposes, it is. It's the disposal site for anything the tire factory can not use elsewhere!

But in a racing tire, the cords on the sidewall are unprotected. So if you have a set of racing tires that are cracking in the sidewall - that's into the structural area of the tires - and that's bad and a good reason to replace them.

BUT!!

The line between pure racing tires and street tires being used for racing is confusing the issue when we talk about "racing tires".

If you are getting circumferential cracks right above the rim line, you probably don't have pure racing tires. (Unless you are being confused by the ends of the fabric.)

And, yes, age degrades the rubber's ability to adhere to the fabric. That's the primary reason everyone is talking about age of tires. Cracking is not the issue. Cacking is only a symptom!

Andyou should be aware that different parts of the tire have different rubber compounds. So cracking in the sidewall might not affect the tread and vice versa.

 

[patprimmer]

These are genuine racing tyres. I will advise they be replaced in both cases.

Regards
Pat
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[CapriRacer]

Pat,

If you can get some photos, that would be even better.

 

[patprimmer]

I am not where the cars are right now

Regards
Pat
See FAQ731-376 for tips on use of eng-tips by professional engineers for professional engineers

 

[CapriRacer]

One last thought.

You ought to get the guys who supply these types of tires to look at them before you decide to throw them out. They are used to seeing these tires and can provide better judgement then I can - especially considering I'm not looking directly at them.

A quick visual will tell an experienced tire guy a lot.