Tyre Failures and Causes
By Dean Smith
Tyre failure is a nagging issue because the retread sector often carries the blame, irrespective of the cause. Throughout my years in the retread industry, I have found there are 8 main reasons for new or retread tyre failures.
Casing failures occur due to the carcass or body of the tyre failing. This could be due to a belt separation, zipper (sidewall lateral rupture), sidewall separation or such which was not found during initial inspection. It has nothing to do with any part of the process (except failure to diagnose at initial inspection), driver fault, or rubber. Many casing failures can be avoided by using Real Time XRay (a new innovation currently being perfected) or Shearography to locate separations etc.
Any retread that fails on the road due to a problem caused during the retreading process. Ordinarily, any process problem will happen within 200 or so miles on the road, anything after this is usually due to other reasons. These process problems could be due to a number of factors such as contamination under the tread, bad skive out repairs, bad repairs or section repairs, curing failures (due to chamber problems) or any other step in the process that does not comply to the recommended quality steps. These are not normal, but do happen if quality is not adhered to.
As with any industry, there are retreaders out there who’s initial objective is quantity and not quality.
A retread has already been proven through at least 1 prior life, so basically is not a proto-type anymore, but an excellent candidate for retreading. Unlike new tyres, a retread is a separate entity and not a part of a mass production facility. Thus, new tyre manufacturers may have to recall thousands of tyres, the retreader may (if a chamber problem goes unnoticed) may have to recall 22- 25 tyres, but this is very rare and problems are normally found before the tyres leave the factory by observing the chamber charts and good final inspection.
We all know through past experience, that the recommendations by tyre and retread companies about specific application of tread pattern and sizes is often ignored by trucking fleets etc.
There are obvious factors that limit such applications. If a tread shows groove cracking, lug chunking, shoulder wear or such, the application is probably wrong. One of the most destructive applications for a truck tyre is on spread axle. The capability of a 40 foot + trailer with wheels spread so far apart to turn, defies the ability to rotate in such a small area but tends to drag. Therefore a rounded shoulder will assist. Not the use of lugs, super wide tyres or 24.5” tyres.
If for logging or quarry work etc, find the correct pattern; rib designs for haulage were not conceived to do this work, and specific ribs and lugs and such to do this job.
Incorrect or no fleet maintenance
This is due to fleet negligence and lack of proper tyre maintenance. I have no idea where to start with this particular issue. TRIB is constantly trying to lay this baby to rest, but seems to be fighting an uphill battle which I hope, with persistence, will prevail.
Tire maintenance and monitoring is the lifeline to trucking!
High blood pressure, low sugar, high cholesterol are all terms we are more than familiar with. It’s a part of modern everyday life. Yet. Low air pressure, overloading, wrong application etc, seems to escape us. There is no pill for tyre maintenance, just common sense!
These occur when truck drivers run over objects, kerb the sidewalls, over/under inflate, overload, puncture and run flat etc. According to truck drivers though, these never happen…..but we, as retreaders, know differently.
Repair material problems
Although very rare, they do happen. Contaminants can enter patches etc in the construction process, cements can be faulty, extruder rope used for filling can be out of date etc.
Cushion gum/AZ strip-stock problems
This is again rare, but when cushion gum or strip-stock has exceeded its shelf life and is either partly or fully cured, the tyre will fail. This could be due to the manufacturer of the gum or stock shipping faulty goods, or the retread factory not storing in a cold room or not paying attention to the expiry dates (this then becomes a problem! Is it a process problem?). Mainly; it is due to not storing at a low temperature, or not allowing the cushion gum removed from the cool room to reach ambient temperature (this removes the sweating, just as a can of soda taken from a refrigerator will create condensation on the can when placed in warmer air, rubber removed from the cool room will do the same).
Faulty tread rubber
This again is also very rare. Tread rubber suppliers can have a number of problems with the tread they supply. Pattern sharpness deficiency (due to lack of rubber in the press, air pockets etc) which will not cause a failure, and is usually only a cosmetic issue. Failures can however occur due to:
Porosity in the tread rubber due to lack of cure, lack of pressure etc. When cut the rubber shows many little air pockets or honeycombs. If the underside of the tread is contaminated with excess mould release lubricant.
If the underside of the tread has not been buffed (rubber will not bond to rubber that has not been prepared).
If the buffed surface has not been cemented to prevent oxidation. The easiest thing in the world is for the retreader to blame the suppliers (which happens very often), finding the reason for a retread failure is not easy, but with the correct training it becomes a detective scenario. A clear reason can be found 99% of the time. It all boils down to trust and experience, and if a rubber company can supply a technical person to inspect the failures, then it becomes a sort of crime scene investigation, and evidence usually is favor of the rubber company…but sometimes not.