How Do I Know if a Run-Flat Tire is Flat?

So you recently got run-flat tires installed on your vehicle. Smart move! These innovative tires allow you to drive up to 50 miles with zero air pressure if you get a flat. But there’s a catch – with run-flats, you can’t always tell just by looking if one of them has lost air. Not sensing an underinflated tire can lead to damaged wheels, reduced control, and safety issues. Thankfully, there are easy ways to check if your run-flat is flat or failing.

Here’s a quick answer:

Unlike normal tires, run-flats can lose significant air pressure without appearing underinflated. Watch for subtle signs of a flat run-flat like sudden vibration, your tire pressure warning light activating, rapid tread wear on one tire, or reduced fuel mileage. The only way to truly check is by using an air pressure gauge to measure PSI and compare to recommended inflation levels for your tires.

What are Run-Flat Tires?

Run-flat tires contain reinforced sidewalls that stay rigid enough to support your vehicle’s weight even with no internal air pressure. They allow you to keep driving if you get a puncture until you can safely pull over out of traffic. Table 1 below shows the key benefits of run-flat tires:

Table 1: Benefits of Run-Flat Tires

BenefitDescription
No need to immediately stopYou can drive up to 50 miles to get to a safe place for repair
Avoid being strandedNo need to change a flat tire on the side of the highway
Maintain controlRigid sidewalls provide stability and prevent wheel damage

Modern run-flats first appeared in the late 1990s on high-end vehicles but have since become common on many models. The reinforced sidewalls give you crucial extra mileage if a tire failure occurs. But this rigid construction also means you can’t detect an underinflated run-flat just by looking at it or feeling how firm it is.

Warning Signs of a Run-Flat Tire Issue

With normal tires, you might notice thinning tread or a very soft sidewall indicating loss of air pressure. But run-flat tires always feel firm and hold their shape even when completely flat. Instead, watch for these subtle signs of trouble:

Vibration or Pulling – If one run-flat tire loses pressure, it can create vibration through the steering wheel or cause the vehicle to pull to one side. Pay attention to any new vibration or handling issues that start suddenly.

TPMS Warning Light – Most modern vehicles have a tire pressure monitoring system (TPMS) with a warning light on the dash indicating low pressure. This should alert you if a run-flat drops 25% or more below its recommended air pressure.

Reduced Fuel Economy – An underinflated run-flat tire creates more rolling resistance which reduces gas mileage. If your fuel consumption suddenly decreases for no apparent reason, it could signal a tire issue.

Excessive Tread Wear – Low pressure in a run-flat concentrates more vehicle weight on a smaller contact patch. You may notice uneven or rapid tread wear signaling an underinflated tire.

While these warnings do not definitively confirm a run-flat tire problem, they indicate the need for a full air pressure check.

Methods to Check Run-Flat Tire Pressure

Since you can’t determine the inflation level just by looking, you need to use a pressure gauge. Here are a few ways to measure run-flat tire pressure:

Tire Pressure Monitoring System (TPMS) – As mentioned earlier, most modern vehicles have a TPMS that shows tire pressures in real time on your dash console. If equipped, the TPMS should warn you of any under-inflation well before it becomes critical.

Digital Pressure Gauge – For frequent checks, get your own digital tire pressure gauge with a built-in LED screen costing around $10-15. Compare readings across tires watching for discrepancies of 8 psi or more.

Tire Shop Air Tower – Every auto service center and most gas stations have an air tower cabinet allowing you to check pressures on all tires. Drive up, connect the gauge pipe, and get accurate psi readings for free.

I recommend verifying run-flat inflation at least once per month when the tires are cool. Compare the measured pressures to the vehicle or tire manufacturer’s recommended level, usually found on a placard inside the driver’s door jamb. If any tire shows at least 25% under the listed inflation level, it likely needs immediate re-inflation.

When to Request Repairs

What if you confirm one of your run-flat tires has lost significant air pressure? As long as the reinforcement allows it to hold shape and enables safe driving, get the tire re-inflated or repaired based on these general guidelines:

  • at least 8 psi under recommended level – add more air
  • at least 25% under recommended level – inspect inside and outside of tire for punctures or other damage
  • 50% or more under recommended level – take to tire shop for replacement evaluation

Losing up to half the air from a run-flat is not uncommon and it should still function with reinforcement intact. But a flat run-flat can fail after driving over 50 miles. At that point, the excessive flexing can cause serious internal damage or result in coming apart. If you must drive an underinflated run-flat over 25 miles, keep speeds under 40 mph while heading to the nearest shop for inspection or replacement.

Re-inflating spreads out pressures evenly but does not fix punctures. So if a shop finds external damage like nails or bulges indicating internal problems, they may recommend replacement instead of patches or plugs.

Extending Run-Flat Tire Life

Here are a few key maintenance tips to maximize performance and longevity from run-flat tires:

  • Check inflation pressure at least monthly to catch any under-inflation right away
  • Have wheels aligned when installing new run-flat tires to prevent uneven wear
  • Rotate tires every 5,000 to 7,000 miles driving to distribute wear patterns evenly
  • Clean tires and wheels regularly to remove grease, road oils, and grime
  • Avoid hitting curbs, potholes or objects in the road which can damage rigid sidewalls
  • Replace run-flat tires after 5 to 7 years regardless of visible tread wear

The reinforced construction gives run-flat tires improved puncture resistance in the crown area. But sharp side impacts against curbs or debris can still cause irreparable damage. With proper maintenance and inflation, quality run-flat tires typically achieve life spans between 30,000 to 40,000 miles.

Drive Confidently with Run-Flat Tires

Equipped with run-flat tires, you should not panic if you pick up a nail or have a blowout. Just remain composed, monitor for any vehicle instability or warning lights, and head to a safe place at moderate speeds. But don’t ignore potential pressure issues — always investigate signs like reduced fuel efficiency or vibration that can signal under-inflation. Know the limits of run-flat capability and remember they absolutely require replacement if driven completely flat for over 50 miles.

Proactively maintaining correct tire pressures maximizes safety and saves money down the road. So follow the guidelines to check your tire pressures regularly, paying special attention to run-flats lacking outward signs of under-inflation. Address any under-inflation promptly, rely on tire monitoring systems, and drive on confidently with innovative run-flat tire technology!

FAQ

1. How much can I drive on a run-flat tire?

Most run-flat tires (RFTs) can be safely driven at speeds up to 50 mph for about 50 miles after a puncture occurs. However, some RFTs may provide a shorter or longer distance capacity, so check your vehicle specifications.

2. Why do I feel vibrations after a run-flat tire is punctured?

A punctured run-flat will cause the tire to become underinflated. Driving on the underinflated RFT can cause vibrations or pulling due to uneven contact with the road surface. You likely need to replace the damaged RFT as soon as possible.

3. If I refill air in a run-flat tire, is it OK to drive on?

No, while a run-flat can hold air after a puncture, the tire is still compromised and should not be re-inflated and driven on for any extensive distances. Even with the sidewalls partially holding shape, an underinflated run-flat has reduced stability and could come apart at higher speeds.

4. Do I have to replace all my run-flat tires at once if one fails?

No, you can safely replace just the failed run-flat tire as long as the replaced tire matches the make, model, and wear level of the other 3 tires. It’s best to replace all 4 RFTs simultaneously for optimal performance, but not required if others show even wear without damage.

5. How do I dispose of a damaged run-flat tire?

Most service shops will remove and properly dispose of your damaged run-flat when replacing it. For at-home disposal, you need to deflate the run-flat fully then take it to your local recycling center or tire disposal facility. Never place old tires with unmatched wear levels or defects back into use on a vehicle.

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