Flat Tire Repairs - Past the Point of No Return(Lea en español)
Whether it occurs during a tire's first mile of use or after thousands of miles of driving, a single cut or puncture can make it necessary to replace a damaged tire that can't be repaired.
The first consideration of evaluating if a tire can be repaired is based on how quickly the driver recognizes they have a problem and how promptly they respond to it.
Because tires require appropriate inflation pressure to carry the load of the vehicle, standard tires should never, ever be driven while low on air or flat (while run-flat tires offer extended mobility in the event of complete air loss, even they may not be suitable to return to service after being driven on while flat).
The telltale external sign of a tire that has been driven on while flat or very low on pressure is circumferential scuffing on the tire's inboard and outboard sidewalls, but external inspection is not enough. Any repairs without removing the damaged tire from the wheel are improper because inspecting the inside of the tire for hidden damage greatly reduces the risk of returning a weakened tire to service. Without dismounting the tire, any hidden damage would likely be missed.
The second consideration when evaluating if a tire can be repaired is to confirm the size, type and location of the damage.
Industry guidelines allow repair of punctures of up to 1/4" in diameter in a tire's tread area. Some manufacturers limit the number of repairs permitted (usually two) and how close they can be (no closer than 16" apart). Repair of any punctures in the shoulder and sidewall areas are not permitted.
Repair of larger tread punctures, long straight cuts and irregular gashes are not permitted. Long cuts have sliced through the tire's steel belts, reducing strength and durability.
While having a flat tire is an inconvenience, returning a permanently weakened or incorrectly repaired tire to service (even as a spare tire) can ultimately have catastrophic results. If there is any doubt, replacing a questionable tire is far safer than repairing one.