What Are Run Flat Tires and How Do They Work?

The world of tires is an ever-expanding nexus of increasingly specialized compounds for any situation. There are tires for everyday roads, snow, rain, summer, racing, off-roading and tires that attempt to handle multiple terrains.

A smaller slice of the tire market is the run flat tire, which usually appears on luxury or heavy vehicles. Basically run flat tires have a contingency built in that allows a driver to continue on the road if it experiences a puncture, allowing them to get somewhere safely for a replacement.

But what exactly is a run flat tire, how do they work and how do you know if you need one? Here's a rundown.

Bridgestone DriveGuard Plus
The Bridgestone DriveGuard Plus is an auxiliary-supported run flat tire. Bridgestone

What is a run flat?

What sets a run flat tire apart from the average road tire is its ability to travel certain distances after receiving a puncture and losing air. This allows you to safely find the nearest auto shop or tire seller for a replacement. Typically they can go about 50 miles at about 50 mph.

The first run flat tires sprouted up in 1935, when Michelin adapted technology used for trains to make a road tire that would run on a safety rim on built-in foam lining when the tire was punctured.

In the 1950's, Chrysler and Goodyear collaborated on the Captive Air run flat tire, which was advertised as having an inner emergency tire that could travel for more than 100 miles if the outer wall was punctured.

Every major tire manufacturer operating today makes run flat tires.

Bridgestone DriveGuard Plus
The Bridgestone DriveGuard Plus comes in most common sizes. Bridgestone

How do run flat tires work?

There are three main technologies used in run flat tires: self-supporting, auxiliary-supported and self-sealing.

The most common choice is the self-supporting run flat. This type of run flat features a reinforced sidewall construction, which has an increased chance of supporting the car in the event of air pressure loss. The sidewall maintains its connection to the rim.

Popular options in this category include the Bridgestone RFT, Goodyear EMT, Michelin ZP, Yokohama Run-Flat and Pirelli RFT.

Auxiliary-supported run flats contain a ring of rubber or a similar material on the interior of the tire, which picks up the slack of the deflated outer tire. This type of run flat is usually found in heavier segments, like military or armored vehicles.

These include Pirelli Scorpion Zero Run Flats, Goodyear Eagle Sport tires, Bridgestone DriveGuard and Michelin Pilot Sport all-seasons.

Bridgestone recently announced the DriveGuard Plus, billed as an improvement on its existing line of run flats.

The company says that the tire, when new, is 12 percent more likely to resist hydroplaning than its DriveGuard counterpart. As the tire wears, it only slips to 8 percent.

Self-sealing run flats come with an extra lining just beneath the tread containing a puncture sealant. That sealant deploys automatically if the tire gets a puncture, usually fixing a hole up to 3/16ths in diameter.

Continental ContiSeal, Pirelli's Seal Inside and Michelin's Selfseal are prominent examples.

Bridgestone DriveGuard Plus
The Bridgestone DriveGuard Plus can go 50 miles after a puncture. Bridgestone

What happens when a run flat tire gets a puncture?

In an ideal scenario, a self-supporting run flat tire would be able to continue driving and support the weight of a vehicle due to the reinforced sidewall.

For an auxiliary-supported run flat, the weight of the flat tire rests on the backup's treads. According to tirerack.com, that shifts the mechanical responsibility of driving on a run flat to the more-sturdy wheel, lifting some of the burden off of the tire itself.

If a self-sealing tire gets a puncture, it depends on if the object sticks to the tire or not. If it remains, the compound forms around the obstruction and seals it off from the rest of the tire. If it doesn't stick, the sealant forms around the hole.

How soon after a puncture do you have to change a run flat tire?

Every tire manufacturer recommends that when arun flat system is being used, you should use the limited distance it affords you to reach a mechanic or tire shop for an immediate replacement.

Keep in mind that while 50 miles and 50 mph is the recommended distance and speed of a run flat tire, it's ideal to keep speeds lower and the distance you have to drive shorter to have a better chance of not having a full blowout.

Bridgestone DriveGuard Plus
Bridgestone

How do you know when you need to change a run flat tire?

Since self-supported run flats have a reinforced sidewall, it can remain stiff despite the natural loss of air pressure over time. Keep a tire pressure gauge handy and check each tire regularly.

If functioning properly (and if you don't feel the sudden loss of pressure), you should be alerted to the problem by a gauge cluster alert from the tire pressure monitoring system.

What cars come with run flats?

Many models sold from Mercedes-Benz, Infiniti, Lexus, BMW, Mini and some Cadillac models come with run flat tires. And manufacturers say that run flat tires are useful on sedans, trucks and SUVs alike, such as the 2022 BMW 3 Series, the 2022 Kia Telluride and 2022 Ford F-150.

The 2020 Ford Explorer became the first vehicle to feature Michelin's Selfseal run flat.

Should I get run flats for my car?

There are several pros and cons to weigh when considering switching to run flats.

On the upside, getting that extra mileage in the event of a puncture could save you some extra hassle in calling a tow truck or changing the tire yourself. It also frees up any space that may have been taken up by a spare tire.

The immediate presence of a backup system also means that the car will be easier to drive, even if it's deflating.

On the other hand, run flat tires are usually more expensive than other tires. For example, a set of four Pirelli P Zero Run Flat tires for a 2022 BMW 3 Series can cost $1,270.40, according to TireRack. A set of non-run flats for the same car, like four Michelin Primacy Tour all-seasons, run for $960. They also represent a small slice of the overall tire market, so supplies may be limited, especially with ongoing supply chain issues affecting every facet of the automotive industry.

Additionally, many cars that come standard with run flat tires don't include a spare. And with a stiffer sidewall, run flat tires ride noticeably more harshly than standard tires. Each buyer will have to weigh the pros and cons, and decide if the premium is worth the payoff.