What is a run-flat tire?

Editor: Ilkka

Last updated: February 7, 2022

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“No no, not now!” is a common phrase people use when they hear a whoosh from their vehicle’s tires while driving. You can already feel what is being talked about here – a flat tire has a way of disorganizing one’s schedule. 

You may not have a spare, the tool kit, or don’t know how to replace a flat tire. Even if you know how to fix it, you may not want to take on such a dirty task on the clothes you’re wearing. 

Whether you can fix it or not, you surely must waste time you can’t get back. To curb these inefficiencies, auto manufacturers have started making run-flat tires.

What are run-flat tires?

Run-flat tires allow drivers to continue driving even when the tires have lost air pressure due to a puncture. While you can’t drive them for a long distance, they can carry you until you get to a repair shop or to a safe place to replace the tire yourself. 

Generally, one can drive 50mph up to 50 miles without air on run-flat tires. However, to play it safe, it’s best to check the manufacturer’s specifications on how long and at what speed one can drive with the run-flats. 

Run flats have existed for a long time, but only recently they have become more popular. Most automakers now make it standard equipment in newly manufactured cars. In fact, run-flats are standard tires in about 14% of new vehicles.

How run-flat tires work?

Run-flat tires work even without air in them, primarily in two ways. They either work as a self-supporting, or with a support ring system. 

In a self-support system, the tires are manufactured with reinforced sidewalls, four to six times thicker than on a conventional tire. If these tires lose their air pressure, they can continue carrying the vehicle’s weight (due to thicker sidewalls), allowing drivers to continue driving for a short distance.

In contrast, the support ring system utilizes a hard rubber. This means that when there is a loss of air pressure, the hard rubber can carry the vehicle’s weight. However, you must use them according to the manufacturer’s specified speed and distance.

Pros and cons of run-flat tires

Pros

You can continue driving with a punctured tire

A run-flat tire will allow you to drive even after losing air pressure due to a nail puncture or other sharp objects. This allows you to continue your journey and get wherever you’re going on time or possibly get to a tire shop. 

In some cases, if your journey will be more than 50 miles, you can drive to a safe place then call a tow truck or roadside assistance. But the fact remains that you’re not stopping immediately because of a deflated tire. This is obviously the major benefit of driving run-flat tires.

punctured tire

Safety

Conventional tires will send a strong signal to the driver when it gets deflated quickly, resulting in a harsh maneuver that can lead to an accident. However, run-flats will keep the vehicle more stable and still run relatively well despite the complete loss of air pressure.

Again, you won’t have to get stuck in a quiet or unsafe place because of a deflated tire. Run-flat tires can also save you from getting crushed. Reports have it that in the US, at least every three to four days, people are killed or injured while trying to change tires by the roadside. Run-flat tires will allow you to drive to a safer spot or to a repair shop before you start replacing the tire.

mechanic replacing a tire in a tire shop

Less weight, more space & improved fuel economy 

Most cars running on run-flat tires usually do not need a spare tire in their vehicles. The absence of a spare wheel or spare tire reduces weight and allows more space in the car for other things. Less weight also helps improve fuel economy. 

Cons

Cost

Run-flat tires are more expensive to replace than conventional tires. They are also prone to fast and uneven wear, which means users will change them faster than the traditional tires. And since you can’t repair them, you will need to buy a new set sooner.  

Vehicles utilizing run-flats must ensure all wheels are fitted with run-flat tires. This means you will need to change all other tires along with the faulty ones.

Availability issues

Most run-flat tires come as original equipment tires. Only a few manufacturers make them as replacement tires. When they experience severe sidewall damage, finding a pair that matches the former is sometimes difficult. Even if you can find one, it’s usually expensive since only a few manufacturers offer them.

Harsh ride

Since run-flats have stiffer sidewalls, they give a hard ride, especially when going through bumps. Though recent run-flats have improved ride quality, they still can’t match the comfort a regular tire gives. 

What kind of vehicles use run-flat tires?

Theoretically, any vehicle can use run-flat tires since they have the same dimensions as regular tires. However, you must ensure your wheels are fitted to use run-flats, else they can overheat.

In addition, it is worth noting that vehicles with run-flats as original equipment comes with TPMS. The tire pressure monitoring system helps notify a driver when one of the tires gets punctured.

So if you intend to use run-flats on vehicles that had regular tires as a standard, you’ll need to install an aftermarket TPMS. It’s the only way to tell if you’re driving a deflated tire since you may not notice the puncture on a run-flat tire otherwise.

tpms

Self-sealing tires

The use of self-sealing tires is another way manufacturers protect new cars from tire blowout inconveniences. However, self-sealing tires should not be mixed with run-flat tires. Even though they accomplish the same goal, they have different working mechanisms. 

Unlike run-flat tires, self-sealing tires make sure the air doesn’t escape from the tire in the first place. These tires are made with a sealant inside. If the tire gets punctured by any sharp objects, the sealant covers the hole immediately after the object flies out or is removed.  However, in order for self-sealing tire to work as intended, the puncture should be near the center of the tread and not wider than 5 millimeters. 

How long is it possible to drive with a flat tire?

As a rule, run-flat tires that lose tire pressure can be driven for the next 50 miles, but at a maximum speed of 50mph. However, it’s best to check out the manufacturer’s specification on miles and speed to drive on flat tires.

With regular flat tire you shouldn’t drive at all. If you continue driving with a flat, regular tire, you may damage the wheel very quickly. If you damage the wheel, you may need to replace that as well – and usually replacement wheel will cost you much more than a replacement tire.

Can run-flat tires be repaired?

Run-flat tires cannot be repaired; most of the manufacturers do not recommend it.  In fact, in many run-flat tires, you will see a text on the sidewall that reads “do not repair.”

This is because detecting the degree of damage inside the tire is extremely difficult, even with the tires removed from the wheel.

Can you mix run-flat tires with conventional tires?

Ideally, it is not recommended to mix run-flats with conventional tires. Combining them can affect the handling characteristics and overall ride quality of the car negatively. This includes driving stability, steering response, and cornering. In most cases, stopping distance is also increased.

Is run-flat technology worth it?

The safety and convenience that come with run-flat tires are a big thing for most drivers and even manufacturers. To them, the benefits of having run-flats are bigger than the downsides. Manufacturers are now adding run-flat technology also to their best tires, which explains how much they have faith in it. But in the end, it boils down to what you prefer.

Make an informed purchase

While run-flat tires have many advantages, the also have some downsides. To ensure you do the necessary research before going for it, at least to know which tire comes standard in a car before purchasing. The best place to get honest answers about a tire’s performance is through users’ reviews.

Final words

Run flats have several advantages. You may need a run-flat tire if you want to avoid changing tires along the roadside, or drive without inconvenient surprises. It can also save you time since you don’t need to wait for roadside assistance or a tow vehicle.  

More importantly, it saves you from getting stranded in an unsafe place or even at night, giving you enough time to reach a safe place to fill air into the tires or replace them. However, people tend to be skeptical about it since it results in harsher rides, coupled with higher replacement cost and availability issues on some sizes and models.

FAQs

How can you tell if a tire is a run-flat?

The best way to tell if a tire is run-flat is by conducting physical inspections. Check out the tire sidewalls for markings or words like run-flat, run on flat, DSST, SSR, RFT, HSR, RF, ZP, etc. 

Are run-flat tires good or bad?

Run-flat tires can increase safety in many situations. They keep the vehicle stable when a blowout occurs,  reduce weight and prevent you from changing tires in unfavorable conditions. However, they also have their downsides which are good to have in mind when making a purchase decision.