How long can you drive on a spare tire?

What kind of spare do you have?

Most cars carry one of two spares: a small temporary "donut" or a full-size tire that matches the others. The rules are very different, so check which one you have first.

• Donut (temporary spare): narrow, light, often on a plain steel wheel. Its sidewall says "temporary use only" and shows a top speed.
• Full-size matching spare: same size and type as your other four tires, often on the same style of wheel.
• Full-size non-matching spare: full size, but a different brand, tread or wheel. Treat it with some care.
• No spare at all: many newer cars carry a sealant kit instead. See a flat tire with no spare.

Not sure? Look at the spare's sidewall. A donut has a size starting with "T", like T125/70D16. The USTMA booklet calls these T-type temporary spares.

How fast can you drive on a donut spare?

No faster than the speed printed on the donut's sidewall or the label near it, and often that is 50 mph. Your owner's manual may set a lower limit, so read it.

A donut is smaller than your normal tire. It turns faster to cover the same road, runs hotter and grips less. That is why the speed limit is low.

• Stay in the right lane on the interstate, or take surface streets.
• Leave more room to stop. Braking and cornering are weaker.
• Avoid potholes and curbs. A donut has thin sidewalls.
• Slow down more in rain. The narrow tread clears less water.

How far can you drive on a donut?

Only as far as you need to reach a tire shop or get a new tire fitted. Common general guidance says around 50 to 70 miles, but your owner's manual is the rule for your car.

The USTMA booklet says there may be limits on the speed, mileage and placement of a temporary spare, and to check the owner's manual. Car makers set those limits for each model. Some are shorter than the rule of thumb.

Plan the shortest trip that fixes the problem:

1. Put the donut on and check its air before you drive far.
2. Drive gently to where the car will sit until the fix.
3. Get a full tire fitted as soon as you can.
4. Put the donut back in the trunk, with its air topped up.

A tire tech can also come to the car with a new tire in your size. See mobile tire replacement.

Can you drive normally on a full-size spare?

Yes, if it matches your other tires in size, type and load rating, and it has good tread and the right air. Then it works like any of your tires.

USTMA suggests a matching full-size spare join your normal tire rotation. That keeps its tread close to the others.

A full-size spare that does not match is different. Drive it with care and replace it soon, especially on all-wheel drive.

Is a donut safe on an all-wheel-drive car?

Only briefly, and only as your owner's manual allows. On 4WD and AWD cars, even small differences in tire size can strain the drivetrain, USTMA warns.

Some car makers say to put the donut on the rear, or to switch off a 4WD mode while it is on. Others give a very short distance. Your manual has the exact rule.

• Never drive a long way on a donut with AWD.
• Never use two donuts on one car at the same time.
• Use the donut only on its own wheel. USTMA says T-type wheels are made for T-type tires.

Is your spare even good?

Often it is low on air, because spares sit for years without anyone checking them. Check it monthly with a gauge, the same day you check your other tires.

USTMA says to check spare pressure monthly and before long trips. A T-type temporary spare needs 60 psi. That is much higher than a normal tire, so add air in small amounts and do not overfill.

What else to look at on the spare

• Cracks: fine cracks in the sidewall or tread grooves mean age.
• Date code: the last four digits of the DOT number give the week and year it was made.
• The wheel: rust or bends on the rim can leak air.
• The tools: jack, lug wrench and any locking lug nut key.

USTMA says a tire's service life can't be judged by its age alone. Heat, storage and use all matter. Follow your car and tire maker's advice, and have an old spare looked at.

What if the spare is flat too?

Don't drive on it. A flat donut can come off the wheel or ruin the rim, so you need air, a new tire or a tow.

• If you have a small air pump, fill the spare to the pressure on its label.
• If it won't hold air, leave the car where it is safe.
• A mobile tire service can bring a new tire if your size is on hand. We check before quoting.

Read what to do with a flat and no spare for the other options.

How do you put a spare on safely?

Only on firm, level ground, well away from traffic, with the parking brake on. If the only spot is a narrow shoulder next to fast traffic, don't do it yourself.

1. Pull off the road as far as you can. Hazards on.
2. Put the car in park and set the parking brake.
3. Find the jack point in the owner's manual. Using the wrong spot can bend the car's body.
4. Loosen the lug nuts a little while the tire is still on the ground.
5. Jack the car up until the flat tire just clears the ground.
6. Swap the tires and tighten the nuts by hand, in a star pattern.
7. Lower the car, then tighten each nut firmly, again in a star pattern.
8. Check the spare's pressure before you drive anywhere.

Never get under a car held up only by the small jack from the trunk. It is made for lifting a wheel, nothing more.

Many cars have one locking lug nut on each wheel. Its key is usually in the glove box, the center console or with the jack. Without it, the wheel can't come off.

What should you tell a tire tech about your spare?

Say which spare you have, roughly how far you have driven on it, and the size of the flat tire. That tells the tech whether the spare can wait and which tire to bring.

• Donut or full-size spare.
• Miles driven on the spare so far.
• The full size code from the flat tire.
• Whether the flat tire has a nail, a cut or a bulge.
• If you have the locking lug nut key.

A photo of the flat tire's sidewall and the hole helps a lot. A small nail hole in the tread may be repairable, so you might not need a new tire. See a nail in your tire.

Keep the flat tire. Even if it can't be repaired, the size code on it is the simplest way to order the right replacement.

When should you stop driving on the spare?

Stop and pull over if the car shakes, pulls hard to one side, or the spare looks low. Those are signs the spare is damaged or losing air.

USTMA's advice for any sudden vibration is to slow down gradually, without hard braking or sharp turns, then pull off where it is safe and look at the tire. If you are on a busy road and feel unsafe, call 911.

More on staying safe at the roadside: a flat tire on the interstate.

When to contact us: Spare on and need a full tire? Send us your details with the size from the tire's sidewall and where the car is parked.