Spare Tire Check, Mounting and Repair

Vehicles come with one of four setups: a temporary compact spare, a full-size spare, run-flat tires with no spare, or a sealant and inflator kit with no spare. Each one gets you home differently. Checking the trunk floor, under the cargo area, or under the rear of a truck tells you which one you have.

A full-size spare gets measured like a road tire when it comes out. Wear bars sit at 2/32 inch, which is where NHTSA advises replacement, and wet grip is already fading by around 4/32 inch.

Owners of cars with only a kit sometimes add a spare later. Ask us whether one fits your vehicle and what it would take.

Read the sidewall of your temporary spare. Most list a maximum speed, commonly 50 mph, and the owner manual lists how far you should drive on it. These tires have shallow tread and a light build, so treat them as a way to reach a shop, not a way to finish a road trip.

While the spare is on:

• Stay under the speed printed on it
• Avoid long freeway stretches when you can
• Expect longer stopping distances and softer handling
• Check its pressure, often about 60 psi, which is far above what your road tires take
• On AWD vehicles, follow the owner manual, since some limit distance to protect the drivetrain

Get your regular tire repaired or replaced soon. Our flat tire repair page explains what happens next.

A spare can be flat, cracked or years past its prime when you need it most. Pressure also falls about 1 psi for every 10 degrees Fahrenheit the outside air drops, so a spare that read right last August can be low in January. We check its pressure against the number on its sidewall, read its date code, look for cracks, and make sure the jack and wrench are present. On trucks with an underbody carrier, we also check the cable and winch, which can rust and seize.

Our spare check:

1. Pressure set to the spare's own rating
2. Date code read. See tire date code guide.
3. Sidewall and tread inspected for cracks and damage
4. Jack, wrench and wheel lock key located
5. Underbody winch and cable checked on trucks and SUVs
6. TPMS sensor noted on full-size spares that have one

Ask for a spare check with any tire service or oil change.

We look at the damaged tire first to see if it can be repaired. Then we mount the repaired or replacement tire, balance it, torque the lugs, and put the spare back in its place with the right pressure. If the TPMS light is on, we check whether a relearn is needed after the swap.

If the tire cannot be repaired, we quote a replacement that matches your others. On AWD vehicles, tread depth matching matters, and the gap is measured in 32nds of an inch against the other three. Whether the old tire can be fixed at all comes down to published repair standards: a puncture 1/4 inch (6 mm) or smaller, in the tread crown only, never the shoulder or the sidewall. See patch versus replace for how that decision works.

If sealant was used, tell us. We clean it out and check the sensor.

Get fully off the road first, even if that means rolling slowly on the flat for a short distance. Turn on your hazards, set the parking brake and put the car in park. On a freeway shoulder with traffic close by, stay in the car and call for roadside help instead of working next to live lanes.

Basic steps:

1. Find the spare, jack and lug wrench. The owner manual shows the jacking points.
2. Loosen the lug nuts a half turn while the tire is still on the ground.
3. Raise the car only enough to remove the flat tire.
4. Mount the spare and snug the nuts by hand in a star pattern.
5. Lower the car and tighten the nuts in the same star pattern.
6. Check the spare's pressure as soon as you can.
7. Have the lug nuts torqued to the foot-pound figure for your vehicle and the flat inspected soon. A re-torque about 50 to 100 miles later is standard practice.

If you have wheel locks, the key is usually in the glove box or with the jack. Without it, that wheel stays on. Our wheel lock page covers what to do if the key is lost.

It depends on the vehicle, and some cars have none. Pickups and many SUVs carry the spare underneath, lowered by a crank through a hole near the bumper or tailgate. That lowering mechanism can rust and seize after years without use, which is a bad thing to discover on the side of the road.

If your car has only a sealant kit, learn how it works before you need it. Sealant can make a later repair harder, so tell us if you used it. Our electric vehicle page has more tire notes for EV owners.