Some repairs are possible but, when in doubt, throw it out.
“We can fix that” is what every customer wants to hear when a flat tire is on the menu, but of course, that isn’t always possible. For your customer’s safety, and for the reputation of your shop, it’s important to know what can and can’t be fixed, and when it’s time for a new tire.
Inspecting the tire
Don’t count on the customer being entirely truthful about how long the vehicle was driven on a flat. Always inspect the tire first for abrasions on the sidewall that indicate driving on it. If you see this, it’s time to look closer.
Even if the tire went flat because of something other than a puncture, such as a leaking rim or valve, take the tire off the rim and check internally for damaged cords or crumbled rubber. If you find this type of internal damage, no matter what caused the flat, the tire must be replaced. The tire should always be dismounted for any repairs, even seemingly minor ones.
The general industry standard is that punctures can be repaired if they are no more than a quarter-inch (6 mm) in diameter (three-eighths for a light truck tire), and located only within the tread face between the outermost grooves, or within two inches of the shoulder. Punctures should never be repaired if they’re in the sidewall or shoulder.
Punctures should be repaired with a patch/plug combination, either two-piece or one-piece, depending on the size and position of the puncture. A plug or patch should never be used by itself.
Manufacturers usually set recommendations for the maximum number of repairs a tire can undergo, and the minimum distance apart. Even so, shops may want to set a policy of no more than two repairs on a tire. The new repair should be at least 16 inches apart from an existing one, and should not be directly opposite the previous repair.
Cuts and tears
Only very small cuts can be repaired. As with punctures, they can be no more than a quarter of an inch long, and in the tread face. They can be repaired like a puncture, providing there’s no evidence of internal damage. If the tears are any longer than a quarter-inch, or in any other area, the tire is scrap.
The customer may be looking at the nail in the tread, but you’re looking at the tread itself, too. If the tire is close to or at the minimum tread depth, don’t bother fixing it, even if the puncture is repairable otherwise. Steer the customer over to some new rubber.
Run-flats open an entirely new conversation on tire repairs because it can be difficult to determine if the tire has suffered internal damage.
The first thing is to check the tire manufacturer’s policy. Some require tire replacement, no matter what. Others may permit repairs under certain circumstances, such as being driven with some air pressure inside, but with such restrictions as only a single repair per tire.
While damage is often visible, such as crumbled rubber inside the tire, it’s possible that the structure has been compromised even though it may not appear to be. Any time a run-flat has been driven when low, and you’re in doubt about its condition, replacement is always the safest step.