October 19, 2011
Knowing what not to repair
RMA procedures take the guesswork out of tire service
By: Kevin Rohlwing
Here is an example where the injuries are in the crown area, but they are so close to each other that the repairs unit would have to overlap. In this instance the driver got lucky because the tread eventually wore out. If this tire had failed, these repairs would probably be blamed.
Nobody wants to tell a customer that a flat tire with good tread depth is junk. In fact, most drivers will accept any repair as long as the tire holds air long enough for them to get back on the road. They will even promise to get it changed out as soon as they get home, but usually return weeks later with the same tire in the same position and a mysterious case of temporary amnesia.
In the old days, the consequences of a marginal tire repair were relatively minor. You would just write “No Guarantee” on the invoice if the injury was in the shoulder or sidewall. If the customer came back and demanded a refund because the tire failed, it was easy to explain that the repair was temporary, therefore, the driver was out of luck. Times have definitely changed.
First of all, there really is no such thing as “No Guarantee” anymore. Every commercial tire dealer is an expert in the eyes of the law, so using these words on an invoice or work order basically amounts to an admission of guilt. While it may prevent a refund in some instances, it certainly won’t play out well in a courtroom should an accident occur as a result of the failed tire.
Just imagine how the testimony will go when the dealer explains why they would not guarantee their work. Look at it like a plumbing company that makes a temporary repair on the natural gas line to someone’s house. One minute the employee falls for a hard luck story by doing a favor for a person who appears to be in need, the next minute the company is in court trying to explain why their employee blew up the house and took out half the block.
“So your employee knew the repair might not hold, but he went ahead and jeopardized the lives of the occupants and the neighbors so the homeowner could save a few bucks?”
Repair guidelines
The primary authority for radial truck tire repair is definitely the Rubber Manufacturers Association (RMA) wall chart. (A sample of the chart can be downloaded for free at website www.rma.org under the Publications tab.) Since RMA guidelines reflect a unanimous consensus among the tire companies, they are virtually indisputable from a legal perspective. As far as commercial tire dealers are concerned, the only type of repair that can be installed in the field is referred to as a puncture, or nail hole, repair.
Puncture repairs are limited to the crown area of the tire, which is the center of the tread approximately 1 to 1.5 inches in from each shoulder. Puncture repairs are also restricted by size and cannot be larger than 3/8 of an inch in diameter. And while truck tires have no finite limits with regards to the number of nail hole injuries that can be repaired, the RMA wall chart says, “The number of repairs may be limited by application, economics, and/or manufacturers’ recommendations.” Regardless of the number of repairs, the repair units cannot overlap (see photo 1) and if the repairs are directly across from each other so that the same radial body cable is injured more than once, the tire cannot be repaired in the field. The reason is that the cable in between the injuries becomes a “floater” that is not anchored by either bead. This creates instability that often leads to a belt separation when repaired with puncture repair materials.
Step by step
As far as procedures are concerned, RMA is very clear on the necessary steps for a puncture repair. While each step in the process is important, there are a few that are vital to restoring the original condition of the tire.
The first is removing the damage using a carbide cutter mounted on a low speed drill with a recommended tool speed of 1,200 rpm or less.
You’ll never find the words “hand-reamer” or “drill bit” in any credible tire repair resource. A carbide cutter is specially designed to cut the damaged steel belt and body cables flush with the surrounding rubber. This stabilizes the area so the void can be filled with a cured rubber insert, which is the second key step.
The RMA is specific on the requirements for filling the void. If the material is not vulcanizing material or a cured rubber stem, then it doesn’t meet industry recommendations. The final step is to seal the injury on the innerliner with a repair unit.
Notice I didn’t use the word “patch.” Repair units are divided into two categories: rubber-reinforced and fabric-reinforced.
While I personally lean toward a fabric-reinforced repair unit in a truck tire, I will acknowledge that the rubber-reinforced variety perform equally as well in the field.
Regardless, the repair material manufacturer has a specified repair unit for every size injury. If that guideline is not followed, then the tire repair will definitely be considered improper.
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