If you've had the unfortunate experience of getting a flat tire, perilously changing it on the side of the road and then driving away on a much smaller temporary replacement (commonly known as a donut) you've probably wondered how long it's safe to drive on it.

While some models of light trucks still come with a full-sized spare tire, most modern cars are only equipped with a temporary spare or no spare at all. There are many reasons for this, including space-saving in smaller vehicles, cost-cutting for manufacturers and also the fact they weigh less which means better fuel economy.

So while donuts have some advantages, the disadvantage is that you cannot drive on it for very long or very fast, meaning that once you've gone to all the trouble of replacing your flat tire (or waited for roadside assistance to come and do it for you) you’re still going to have to drive directly to the closest tire dealership to get a full-sized tire installed. 

What makes a donut different from a regular tire?

Like the name suggests, a donut is small, round, and thick, resembling an actual donut, and looks distinctly different from a regular tire. Because it is narrower and more lightweight, handling and braking are reduced and they can damage your drivetrain if you drive too fast. It is recommended that you drive at a speed of up to 50 mph and a maximum distance of 50-70 miles over the course of one to two days at most. Ideally, you would drive to the nearest tire dealership as soon as you can and change out the punctured tire with a full-sized replacement, but in certain situations this might not be possible. I.e., you get a flat tire late at night and nothing is open. In this case, you’d make the second trip on the day you can schedule a time to get a regular tire installed. 

If you’ve just purchased a vehicle or are using a rental, you should check first of course, that you have a spare tire. Check your trunk or manual to determine the type of spare tire (if any) you have. If you don’t have a spare, consider carrying a tire repair kit or portable air compressor with sealant as a backup. And regularly check the pressure in your donut because even then they are unused, they lose air over time.

What if you have run-flat tires?

Run-flat tires are special tires designed to keep working temporarily even after a puncture or complete loss of air pressure, so you don’t have to pull over right away to change a flat.

They have reinforced sidewalls or internal support rings that allow them to carry the vehicle’s weight for a short time without air pressure. Similarly, you can only drive up to 50 mph and no further than a 50-mile distance (for most), which gives you less driving time than a donut, but at least you don’t have to pull over to the side of the road and change a tire.

How do you know if you have run-flat tires?

Typically, the sidewall will indicate if it’s a run-flat tire with a code or terminology such as:

RFT (Run-Flat Tire)

ROF (Run On Flat) – used by Goodyear

ZP (Zero Pressure) – used by Michelin

SSR (Self-Supporting Runflat) – used by Continental

DSST (Dunlop Self-Supporting Technology)

If you’re still unsure, you can also ask the manufacturer whether it was originally equipped with run-flat tires. If your car has no spare tire or tire tools and came with a tire repair kit or inflator, it's likely equipped with run-flats. If you provide your VIN to the manufacturer, they’ll be able to check this. Additionally, if you know the brand and model of your tire, you can look it up on their website to confirm whether it's a run-flat tire.

Regardless of whether your vehicle has a spare or run-flats, you’ll want to check your vehicle’s manual for manufacturer-specific limits. If you’re not sure what you have, check your trunk, undercarriage, or tailgate or look in your owner’s manual under the “tires” or “spare tire” section.

And as a good back-up, it's generally a good idea to have roadside assistance coverage and have their number saved in your phone.

To read more safe driving tips, check out this previous blog article:

Checklists for Safe Driving in all Seasons

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