Spare Tire Types: Full-Size, Donut, Repair Kit and More

Find out before you need it

The worst time to learn what your car carries for a flat is on the shoulder, in the rain, with traffic going by. Lift the trunk floor or check the owner's manual this week, and you'll know which of these four you're working with.

Full-size spare

A full-size spare is a fifth tire and wheel the same size as the four on the car. Goodyear splits these into two kinds:

• Matching. Same tire and wheel as the other four. Goodyear notes it also keeps the car looking the way it should.
• Non-matching. Full size, but a different tire or a plain steel wheel. It works as a spare; treat it as a way to get to a shop.

The trade-off is space and weight, which is why fewer cars carry one. The upside, as Goodyear puts it, is that you may not have to drive straight to a repair shop after a flat.

Two things to check on a full-size spare: pressure, against the door placard, and age. A spare that's never touched the road still ages. Our guide to the DOT date code shows how to read when it was made.

Compact temporary spare (the "donut")

This is the most common spare: a narrow tire on a small wheel, built to get you off the road and to a shop.

Goodyear describes compact temporary spares as lightweight with a shallow tread depth, with much smaller dimensions than a regular tire. Michelin adds that they have less load capacity than your regular tires and aren't built for normal driving.

The limits are printed on it

Temporary spares carry their limits on the sidewall or on a label nearby. NHTSA's interpretations of the federal tire standard describe temporary-use spares marked with wording like "Temporary use only", an inflation pressure, and a 50 mph maximum speed.

What the makers say:

• Speed. Michelin says not to exceed 50 mph on a compact spare, and to avoid aggressive acceleration, hard braking and sharp cornering.
• Distance. AAA's general advice is to drive no more than 50 miles on a donut-type spare before replacing it with a regular tire.
• Your car's numbers win. Michelin's advice is to check the spare's own sidewall for its restrictions, because they vary. The owner's manual has them too.

In practice, a donut is a ride to a tire shop, not a plan for the rest of the week.

Run-flat tires

Some cars carry no spare because the tires themselves are the plan. A run-flat keeps carrying the car for a limited distance after it loses pressure.

The limits are set per product. Bridgestone and Michelin both quote up to 50 miles at up to 50 mph for their run-flat lines, and Goodyear says driving deflated on its run-flat tires is restricted to a maximum of 50 mph for up to 50 miles. Load, heat and how you drive affect how far you actually get.

Because a run-flat can look normal when it's flat, it depends on a working TPMS warning. Our run-flat tire guide covers how they work and when they can be repaired.

Sealant and inflator kit

Many newer cars come with a kit instead of a spare: a bottle of sealant and a small 12-volt compressor. AAA's 2017 research found nearly one-third of new vehicles were sold without a spare tire.

AAA's view of the kits is clear about the limits:

• They can temporarily repair small punctures.
• They can't fix sidewall damage or blowouts, or larger leaks.
• The sealant has a shelf life; AAA puts it at four to eight years, so check the date on yours.

Use only the sealant your vehicle maker specifies. Tesla's manual, for example, warns that other sealants can damage the tire pressure sensors. A sealant fix is temporary; the tire still needs a shop inspection afterward. Our patch vs plug guide explains what a permanent repair involves, and the repairability check shows where your puncture falls.

EVs often fall in this group. Teslas generally don't come with a spare; see our guide to a Tesla flat with no spare, and our EV tire guide for how EV tires differ.

Checking the spare's pressure

NHTSA's advice is to check pressure monthly on every tire, spare included, with the tires cold. The spare is the one everybody forgets, and a flat spare is no spare.

1. Find the right number. A full-size spare usually matches the door placard. A compact spare usually needs much more air: Goodyear says generally 60 psi. The spare's sidewall or label, or your owner's manual, has the figure for yours.
2. Check it cold with a gauge, the same way you check the other four.
3. Look it over. Cracks or bulges are reasons to have it inspected. A bubble in any tire is a stop sign; our sidewall bubble guide explains why.
4. Check the jack and tools are where the manual says they should be.

After you've used the spare

Get the original tire inspected promptly. If it can be repaired, the shop does it from the inside with the tire off the wheel. If it can't, you'll need a replacement that matches the size, load index and speed rating on your door placard. The Tire Size Finder reads that sticker for you, and you can shop tires by size.

Extreme Tires installs at the Sunrise shop or by mobile van in Miami-Dade, Broward and Palm Beach counties, so a mobile van can come to you if you're on a donut. Anywhere else in the 48 contiguous states and DC, we ship to your address for a local installer. See how installation works, or call (954) 773-1896.