Establishing the repairability of a tire begins with a visual inspection. Always inspect tires before doing any repair on the tire itself.
Tires that are worn to the tire’s treadwear indicators -- or to 2/32nds-inch remaining tread depth in any area of the tread -- should not be repaired. If the tire has more miles left on it, move forward with the evaluation.
Before removing the tire from its wheel, check the location of any leaks on the tire’s surface and around its valve stem. Use a soapy solution or water; bubbles will indicate any leak(s).
Once located, mark the injured area with a tire crayon, then deflate the tire and remove it from the wheel. Be careful not to cause further damage, especially to the bead area. Spread the beads to get a good look inside and mark the injury area on the inner liner with a tire crayon.
Good lighting is necessary, especially on the surface area being inspected. A hand-held inspection light often provides enough light to inspect both inside and outside the tire properly.
When an object, such as a nail, breaks through a tire’s innerliner, the immediate concern is the loss of inflation, but the long-term risk is the instability around the injury site that can lead to tread separation.
Many times, a nail in the tread can cause severe damage to the sidewall -- damage that cannot be seen on the outside of the tire. Note that only damage to the crown or tread area of the tire can be repaired. If there is damage to the sidewall or other parts of the tire, the tire must be scrapped.
Never repair tires with a tread puncture larger that ¼-inch (6mm).
Never repair a tire that has a non-recommended previous repair.
If the injuries to the tire overlap, the tire cannot be repaired and should be replaced.
Assuming the tire can be repaired properly to industry standards, the final step is inspecting the work that was performed, paying attention to the location of the repair, the beads and the valve. If the tire is still losing air, rework the repair as necessary until the issue is solved or another recommendation is made.