What Are Run-Flat Tires and Are They Right For You?
Run-flat tires have been around for decades, but that doesn't mean everyone knows what they are. We're here to get you up to speed, so to speak.
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First introduced in the 1930s as a safeguard against blowouts, today’s run-flat tires are a variant of years of race car innovation and technology. And like other innovations, like disc and antilock brakes, fuel injection and steering wheel controls, one day these tires may become standard equipment on some vehicles. For now, run-flat tires have pros and cons, so let’s see if they are the right choice for you.
What Are Run-Flat Tires?
Simply put, run-flat tires allow you to drive safely to a repair shop or level area when a tire is punctured and loses air pressure. These tires are designed and constructed to support the weight of your vehicle with little or no air pressure. In regular car tires, the air pressure supports the weight of a vehicle. It is not supported by the tire itself.
There are two types of run-flat tires
Self-supporting run-flat tires are most commonly used on today’s passenger cars and may have a symbol that resembles a snail on the sidewall. According to Jim DeLeo, Northeast Division Manager for Hunter Engineering, sidewalls on run-flat tires can be four to six times as thick as a conventional tire sidewall. The denser sidewall keeps a deflated tire from collapsing.
Supporting-ring system run-flat tires employ a stiff rubber (or other rigid material) ring attached to the tire or wheel bead. (The bead is where a tire seals itself to the wheel assembly.) The tire’s tread rests on the support ring that carries the vehicle’s weight if a tire losses air pressure. This design is used on heavy-duty trucks and military vehicles, and comes with a symbol that looks like Pac-Man eating a hot dog.
Don’t confuse run-flat tires with self-sealing tires. Self-sealing tires are conventional tires with a layer of sealant that coats the inside of the tire over the tread area.
Run-Flat Tires vs. Regular (Conventional) Tires
- Radial-ply construction;
- Same numeric marking scheme and physical dimensions;
- Sustain interior sidewall damage from overheating when driven with low/no air pressure;
- Sustain exterior sidewall damaged from hitting a pothole, bouncing into a curb or getting walloped in an accident;
- Should always be replaced in pairs.
- Sidewalls are strongly reinforced with Polyimide and glass fibers having very high tensile strength to support the vehicle if a tire loses air pressure.
- Due to their stiff, reinforced sidewalls, run-flat tires have different handling characteristics.
- More expensive to replace. For example, at a major online tire retailer, a run-flat all-season tire costs almost $100 (or one-third) more than its same-size conventional counterpart.
Additional unique features of run-flat tires:
- Wheels designed specifically for run-flat tires have a second bead (called a safety bead) that helps keep run-flats well secured and properly seated onto the wheel when driving with low/no air pressure;
- Steering and handling will remain close to normal after losing tire pressure;
- To reduce weight and increase gas mileage, a spare tire and tire changing tools may be optional on vehicles that come with run-flat’s as standard equipment;
- Trained technicians using sophisticated equipment are needed to dismount/mount run-flat tires.
Can Run-Flat Tires Be Patched Or Repaired?
Most tire manufacturers do not recommend repairing run-flat tires. After driving a severely underinflated run-flat tire, even with the tire removed from the wheel, detecting and confirming internal tire structural integrity can be extremely difficult. In fact, many run-flat tires have “Do Not Repair” imprinted on the sidewall.
What Kind of Vehicles Can Use Run-Flat Tires?
In theory, because run-flat tires have the same physical dimensions as conventional tires, any vehicle can use them. However, unless your wheels are designed for run-flats, they can overheat and separate from the wheel bead — the same as a conventional tire — when driving with low/no air pressure. In addition, because you may not recognize if one of your tires is flat, your vehicle needs a working tire pressure monitoring system (TPMS). All vehicles that come with run-flats as standard equipment are required by law to come with a TPMS. If you plan to install run-flat tires on a vehicle that came standard with conventional tires, easily installed after market TPMS are available.
CAUTION: A brass valve core will corrode when used in an aluminum tire pressure sensor valve stem. Use nickel-plated valve cores with aluminum tire pressure sensor valve stems.
How Long Can You Drive on a Run-Flat Tire When Flat?
If your TPMS shows low or no air pressure, the rule of thumb is you can drive up to 50 miles at 50 MPH on a run-flat at zero air pressure. Once there is no air pressure, run-flats can’t be driven on indefinitely. Get to a repair shop, or if you have the optional spare tire, install it as soon as possible.
Can Run-Flat Tires Be Replaced With Conventional Tires?
Yes, and you can use the run-flat wheels. But be aware, if run-flats came as standard equipment:
- Replacement conventional tires should meet your vehicle’s manufacturer recommended size, speed rating, load capacity and inflation pressure specifications to ensure wheel, TPMS, speed and anti-lock brake sensor readings are not affected;
- Your vehicle probably did not come equipped with a spare tire, or tire changing tools, so you’ll have to purchase them;
- Suspensions tuned for run-flat tires will have a different road feel with conventional tires.
Can You Mix Run-Flat Tires With Conventional Tires?
Unless it’s an emergency or a short-term fix, never mix run-flats with conventional tires on the same vehicle. Mixing run-flat and conventional tires can negatively impact steering response, driving stability, cornering and it can increase braking distance.
The Final Word
If you want to avoid changing a flat tire and live within 50 miles of a repair shop, run-flats may be a good option for you. Many people enjoy the benefits of run-flat tires. They increase safety if you are unable to change a flat tire, especially on a highway or at night, and they may save you from having to wait for road service assistance because your alloy wheels are corroded and stuck onto steel axle hubs. However, some people question their value due to the harsher ride and higher replacement cost, and choose to replace them with conventional tires.