Run-Flat Tires: How Do They Work?
They're rated to drive up to 50 miles at 50 mph after a puncture.
A tire’s basic construction hasn’t really changed all that much since its invention. There have been upgrades, sure, but one of the biggest technological leaps for tires occurred with the creation of run-flat (RF) tires.
We’ve all been by the side of the road, cars and semis whizzing past our heads as we pray that the spare we’ve neglected in our trunk is still inflated. After popping the trunk, we find that we used it ages ago on the other side of the car. Now stranded and without an extra spare or can of Fix-a-Flat, all we can do is curse the heavens and call a tow. It is this type of situation that run-flats aim to fix.
As the name suggests, run-flats are tires that can be used even when punctured. These tires can be run for a specific distance even while “flat.” But do you know how they work? Never fear, Car Bibles’ editors are here. Let’s discuss run-flat tires and why they’re both a boon for motorists and despised by enthusiasts.
How Do Run-Flat Tires Work?
A run-flat tire is similar to your standard pneumatic tire, except it’s been designed to continue working after being punctured. The magic does have its limitations, though, as you can only drive on run-flats at reduced speeds, roughly 50 mph or slower, and short distances, about 10-50 miles or shorter, to get somewhere safe so the tire can be replaced or fixed.
Run-flat tire construction can be broken into three different types: self-supporting, auxiliary-supported, and self-sealing systems. Here’s how the three work and differ.
Self-supporting run-flat tires are actually an older design, with origins dating back to the 1930s. The basic design premise of a self-supporting run-flat tire is that the sidewall is reinforced, and an inner lining prevents air loss when punctured. These were originally marketed to banks and the military as “bulletproof” tires.
Self-sealing run-flat tires are pretty simple in their design. What you have is an extra lining within the tire’s construction designed to seal around a puncture. That’s it.
Auxiliary-supported run-flat tires work differently than the self-supporting and self-sealing systems. Instead of reinforcing the tire or material designed to seal punctures, auxiliary-supported run-flat tires feature a ring of hard rubber or other materials outlining the wheel’s rim. The idea is that this material can and will support the weight of the car, including its passengers, when there is a sudden loss of air in the tires due to a puncture.
These types of run-flat tires are now used mostly by the military and security industries since they guarantee safe and continued travel.
Benefits of Run-Flat Tires
Safety is the biggest benefit. On average, they can get you from the initial point of puncture to a safe location up to about 50 miles away. That should be enough for you to reach the nearest auto-repair shop.
Another good thing about them is that you don’t have to panic when your tire-pressure monitoring system (TPMS) on your car’s dashboard starts blinking. With run-flats, you don’t have to do anything dangerous such as switch lanes right away or attempt to swap a tire with traffic whizzing past you.
Drawbacks of Run-Flat Tires
Although RF tires can be beneficial in the case of an emergency or flat tire, they aren’t without a few shortcomings. First off, they tend to be more expensive than regular tires, so they increase the costs of regular maintenance.
Another downside is that the driving experience isn’t as good as conventional tires. Because these tires are designed differently, they don’t provide a smooth driving experience. Noise, vibration, and harshness all reverberate more easily into the vehicle’s cockpit. This is particularly true when you are riding on a road full of potholes.
Because of their construction, run-flat tires tend to be heavier than normal tires. This translates to lower fuel efficiency and more unsprung weight, reducing the car’s handling.
How To Identify Run-Flat Tires
The simplest way to identify a run-flat tire is look at the tire’s sidewall. It might literally say “run flat” on it, or it might have letters that are specific to the manufacturer. For example, you might see ZP, SSR, ROF, EMT, RSC, RFT, or DSST.
How Long Can You Drive on a Flat Tire?
Most RF tires are designed to run a maximum of 50 miles after a puncture while driving at 50 mph or slower. Check your exact tire’s specifications for more information. As a rule, drive as slow and as short of a distance as possible to get to your house or garage.
Can Run-Flat Tires Be Repaired?
According to Tire Rack, “even a trained tire specialist may be unable to confirm internal structure damage resulting from a run-flat tire having been driven in a severely underinflated or zero pressure condition.” That’s not always the case, however. Goodyear says that certain models of its run-flat tires can be repaired. If it were up to us, we’d always replace a damaged tire, but consult a tire professional.
Do Run-Flat Tires Last as Long as Normal Tires?
Conventional tires last approximately 40,00-50,000 miles, though this largely depends on where you drive, how you drive, and various other factors. Different run-flat tires have different ratings, so their lifespans are also different, though it’s not dramatically different from conventional tires. As with any tire, just monitor your tire tread and replace when necessary.
FAQs About Run-Flat Tires
Car Bibles answers all your burning questions.
Q. Are run-flats available for all cars?
A. You can get a run-flat tire for most cars, but you’ll need to check that the tire manufacturer makes a model for your car’s specific tire size.
Q. What is a tire-pressure monitoring system (TPMS)?
A. A tire-pressure monitoring system (TPMS) is now standard on every new car and is designed to show you your tire’s air pressures. This helps alert you when they’ve lost pressure or have more pressure than the manufacturer-specified amount.
This system links pressure sensors within your tire to your car’s ECU and either details the specific pressures through a car’s infotainment hub or will alert of a pressure change with a triangle and cross-section of a tire with an exclamation point symbol in the car’s dash for older vehicles with TPMS sensors.
Q. Can you put regular air in run-flat tires?
A. Run-flat tires take the same type of air your normal tires do, including those that run with nitrogen.
Learn More From This Video Tutorial About Run-Flat Tires
Not everybody is a text-based learner, so we made sure to include a video explanation as well. Check it out below.
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