Spare Tires Decoded: Donut, Full-Size, and How Long They Really Last

Most Calgary drivers don't think about their spare tire until they need it. By then it's flat, the wrong size, or in the case of a lot of newer vehicles, not actually there at all. Spare tires come in three flavours these days — donut, full-size, and "we replaced your spare with an inflator kit" — and each has different rules for how long you can drive on it, how fast, and what to do when the spare is also done. Here's the honest breakdown of donut vs full-size spare tires, what's in your trunk right now, and the maintenance you should be doing on the spare you've ignored for the last five years.

Table of Contents

• The Three Types of Spare in Modern Vehicles
• Donut Spares: Rules and Limits
• Full-Size Spares: When You Have Them, How to Use Them
• If You Don't Have a Spare at All
• Calgary Spare Tire FAQs

The Three Types of Spare in Modern Vehicles

Walk into the trunk or under the cargo cover of any vehicle sold in Canada in the last 15 years and you'll find one of three setups.

1. Compact "donut" spare. A skinny tire on a small wheel, designed for short-distance, low-speed emergency use only. Most common in passenger cars and small SUVs. The donut is intentionally smaller than your regular tires to save trunk space and weight.

2. Full-size matching spare. A regular tire on a regular wheel, identical or very similar to the four on your car. Common in trucks, larger SUVs, and some traditional sedans. Mounted under the bed, in the cargo well, or hung off the rear in the case of trucks and Jeeps.

3. No spare — sealant kit and inflator instead. Increasingly common in newer cars (especially BMWs with run-flats, hybrids, and EVs) for weight and space reasons. The "spare" is a can of tire sealant and a 12V inflator that can fix a small puncture but does nothing for a sidewall blowout, a bent rim, or a hole bigger than the sealant can plug.

Check yours now if you don't know what you have. Lift the cargo cover, pull up the trunk floor, or look under the rear bumper.

Donut Spares: Rules and Limits

Donut spares are designed for "get to the tire shop" use, not "drive the QE2 to Edmonton" use. The standard limits printed on most donut sidewalls:

• Maximum speed: 80 km/h (50 mph)
• Maximum distance: 80 km (50 miles)
• Inflation pressure: 60 PSI cold (much higher than your regular tires)
• Acceptable use: Front or rear axle, single corner only — never two donuts at once

Why the limits? The donut has a smaller diameter than your other tires, which throws off the speedometer, ABS, traction control, and (on AWD vehicles) the differential. Driving on it longer than the spec abuses the drivetrain. The smaller contact patch and stiffer construction also handle worse than a regular tire.

If you're driving on a donut and you have to take Deerfoot or Stoney Trail to get to the tire shop, stay in the right lane and do 70 km/h max. Get the proper tire sorted that day, not next week.

Full-Size Spares: When You Have Them, How to Use Them

Trucks, larger SUVs, and most Jeeps come with a real full-size spare. The good news: you can drive on it indefinitely, at full speed, without abusing the drivetrain. The catch: full-size spares need maintenance most owners never do.

The maintenance you owe a full-size spare:

• Check the pressure every 3 to 6 months. Spares slowly lose air just like the tires you drive on.
• Read the DOT date on the sidewall. A 12-year-old spare is past its useful life regardless of how new it looks. See our DOT date guide.
• Inspect for UV cracking. Spares mounted exposed to the sun (Jeeps, some SUVs with rear-mounted spares) age much faster from UV.
• Rotate it into the regular tire rotation if your truck supports it. Some trucks support 5-tire rotation.

If your full-size spare is the same size as your other tires, you can technically use it as a permanent replacement after a tire failure — though our 20% rule guide covers when one spare is enough vs needing a full set.

If You Don't Have a Spare at All

If your car came with a sealant kit instead of a spare, here's the practical reality:

• Sealant works on small punctures in the tread. A nail in the centre tread, no problem.
• Sealant does nothing for sidewall damage, blowouts, or bent rims. All of which are common in Calgary.
• Sealant can void some tire warranties. Once injected, the tire often has to be replaced rather than properly repaired.
• Roadside assistance is your real backup. CAA, your manufacturer's roadside, or your insurance company.

Many Calgary drivers in this situation buy an aftermarket compact spare and a basic tool kit to keep in the cargo well. For run-flat-equipped vehicles, see our run-flat tire breakdown for what your tires can handle without a spare.

Calgary Spare Tire FAQs

How long can I drive on a donut spare?
80 km at 80 km/h max. After that the wheel bearing on the spare's axle starts to overheat and the tire itself isn't designed for sustained use.

Can I use a donut on a snowy day?
You can, but reduce speed even further (40 to 50 km/h) and stay off highways. Donuts have very poor snow performance.

What pressure should my spare be at?
Donut spares: usually 60 PSI cold (check the sidewall). Full-size spares: same as your regular tires per the door-jamb spec. Either way, check every 6 months.

If I have run-flat tires, do I need a spare?
Most cars with run-flats don't include a spare from the factory.

Can I use a regular tire as a spare on an AWD vehicle?
Only if it's the exact same size and similar tread depth as the other three. Otherwise, the AWD differential will be damaged. See our mismatched tires guide.

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Free spare tire check

When was the last time you checked your spare? Bring the car in and we'll pull the spare, check pressure, read the DOT date, and inspect for damage. Five minutes, no charge.

Prince Tires
111 42 Ave SW, Calgary, AB
(403) 452-4283
Book your appointment