When Does a Flat Tire Need to be Replaced?
Here’s when you’re going to have to replace a flat tire rather than having it patched:
- The tire has a sudden loss of air and you drive on it flat.
- The tire is making a “fwump, fwump, fwump” sound when it rolls. This is a sign of internal damage, such as tread separation, which can’t be fixed.
- The sidewall has a puncture, a cut exposing the cord, or a visible bubble or bulge.
- The shoulder has any damage, even if it’s a small puncture.
- You spot a bulge on the tread (often following an impact).
- There’s a gash deep enough to have cut into one of the steel belts.
- The size of the wound in the tread is greater than one-quarter inch.
- You have some types of run-flat tires.
- The tire has been repaired before and the new injury is close to the previous patch. Or the manufacturer doesn’t recommend one or more repairs. (Check your owner’s manual and/or tire warranty.)
- The tread is worn to the treadwear indicators or to 2/32 inch tread depth.
Today’s tires have lower profiles. Their shorter sidewalls mean it’s easier to permanently damage a tire when it’s driven while underinflated. The heat generated is so great it can break the sidewall down in seconds. Rolling on a severely low tire for as little time as it takes to move from the fast lane to the shoulder can make it beyond repair.
Slow Leaks in the Contact Patch Can Be Repaired
If you have a slow leak from a nail or screw that stays lodged in the main part of the tread, chances are good that the tire can be fixed. It may cost you nothing (depending on your warranty) or up to around $35. Done right, your repaired tire should be safe to drive on for its full tire life.
Tire repair is a job for a professional, to protect the nylon and steel cords inside from more damage. First, the tire technician will identify the location of the leak and make sure there are no others by submerging the tire and wheel in water. Then they'll demount the tire, inspecting it inside for structural problems and outside to make sure there's sufficient tread left. If the hole is too close to a previously patched area or on the same body cord as a previous repair, the tire will be too weakened for a new repair.
If the flat is repairable, they’ll start by buffing the injured area being careful to avoid any damage to the liner. Buffing too deep could expose the cords and ruin the tire. Then they’ll use vulcanizing compound and a one- or two-piece plug patch combination to fill the hole and seal the liner.
This method ensures an airtight seal.
What About Plug or Spray Repair Kits?
If your vehicle doesn’t have a spare, you may be relying on a tire plug or sealant kit when you get a flat. These aren’t substitutes for proper repair.
Driving a plug in at the wrong angle can break more of the internal cords that provide tire strength, causing permanent damage. Aerosol sprays may get you out of an emergency situation on the side of the road but they may also cost you. Such sprays can damage TPMS sensors, which run $45 to $200 to replace.
When You’re Not Sure About Replace vs. Repair
Go to any reputable tire store. You should get an answer in minutes on whether a flat is beyond repair. (Les Schwab Tire shops also fix most flats free.)