Out-of-Round Tires: Symptoms and Testing Methods

What is an out-of-round tire?

A tire is designed to be a geometrically smooth and uniform circle. When a tire is out-of-round, its tread radius varies around the circumference. This means that as the wheel spins, the tire effectively gets slightly taller and shorter with each revolution. The tire industry uses the terms radial runout and lateral runout to describe these deviations.

Radial runout is the variation in the tire's radius when measured from the center of rotation. Lateral runout is the side-to-side wobble of the tread or sidewall. Both types of runout create a rhythmic imbalance in the rotating assembly, leading to vibration that is often speed-dependent.

The internal structure of a tire, including the carcass and belts, can contribute to runout. For example, a radial ply tire has cords that run at substantially 90 degrees to the centerline of the tread, per the National Highway Traffic Safety Administration's Federal Motor Vehicle Safety Standard No. 139. If the belts or carcass are not perfectly concentric, the tire may exhibit runout.

How radial and lateral runout cause vibration

When a tire rotates, any radial runout forces the wheel to move up and down slightly. That vertical motion is transmitted through the suspension to the vehicle's body. At certain speeds, this motion can excite a resonance in the chassis, producing a noticeable shake. Lateral runout causes the tire to push sideways, which can make the steering wheel shimmy or pull to one side.

The severity of the vibration depends on the amount of runout and the speed. Even a small amount of runout can be felt at typical highway speeds. Because the tire is the only contact patch with the road, any geometric irregularity becomes a source of force variation.

It is important to note that a tire can be perfectly balanced (no weight imbalance) and still cause vibration if it is out-of-round. Balance machines spin the tire to find heavy spots, but they do not measure the tire's roundness. For more on balancing, see tire balancing.

Common symptoms of an out-of-round tire

The most obvious symptom is a vibration in the steering wheel, the seat, or the floorboard that appears at certain speeds and often disappears at others. The vibration may be constant or occur in a pulsing rhythm.

Other signs include a low-frequency rumble or thumping noise that increases with speed, uneven tread wear that appears as flat spots or scalloped wear, and a vehicle that seems to bounce or hop at highway speeds.

These symptoms can also be caused by other issues, such as wheel imbalance, bent rims, or suspension problems. That is why proper diagnosis is essential. If you feel vibration mainly at speed, see tire vibration at speed.

Shop tests to confirm an out-of-round tire

To confirm that a tire is out-of-round, a professional technician will typically use a tire uniformity machine. This device mounts the wheel and tire assembly, spins it under a load, and measures radial and lateral force variations. It provides a numerical reading of runout, often in thousandths of an inch, and flags the tire if it exceeds the manufacturer's tolerance.

A simpler method is to use a dial indicator on the tire's tread and sidewall. The technician places the dial indicator against the tread and slowly rotates the tire, recording any deviation. This method measures actual geometric runout rather than force variation.

Balancing the tire first can rule out weight imbalance, but it does not cure runout. Some shops also perform a road-force test, which simulates the tire rolling under load on a drum, to identify runout that only appears under load.

According to the Tire Industry Association, proper training of service technicians is critical for accurate diagnosis. Their training programs emphasize that a tire should be inspected both on and off the vehicle to isolate the cause of vibration.

Interpreting test results and acceptable limits

Tire manufacturers set limits for both radial and lateral runout based on the tire's size and type. These limits are part of the tire's specifications and are usually found in service manuals or manufacturer publications. A tire that exceeds these limits is considered defective and should be replaced.

It is important to remember that a tire that is slightly out-of-round may be acceptable in some cases, especially on larger or more aggressive tread patterns. The technician will compare the measured values to the vehicle manufacturer's recommendations.

If testing reveals that the tire is within limits, the vibration is likely coming from another source, such as a bent wheel or an issue with the suspension. In that case, further diagnosis is needed.

Repair or replace an out-of-round tire

Unlike a simple puncture, an out-of-round condition is a structural issue. It cannot be repaired by patching or shaving the tread. The only reliable fix is to replace the tire.

If the tire is still under warranty, the manufacturer may replace it at no charge. Otherwise, you will need to purchase a new tire. When selecting a replacement, consider your driving conditions and the other tires on the vehicle.

For most passenger cars and SUVs, a quality all-season tire is a practical choice. If you live in a snowy climate, a winter tire may be better for the cold season. Always match the replacement tire's size and speed rating to the other tires.

What to pick for your use

Questions

Can an out-of-round tire be balanced?

Balancing adds weights to correct weight imbalance, but it does not fix a tire that is physically out-of-round. A severely out-of-round tire will still vibrate even after balancing.

How much does it cost to test for out-of-round?

Most tire shops charge a diagnostic fee to test and measure runout. Some may waive the fee if you purchase a new tire from them. Costs vary by shop and location.

Will an out-of-round tire damage my car?

Yes, driving on an out-of-round tire can cause accelerated wear on suspension components, wheel bearings, and may cause uneven wear on the other tires. It is best to replace it promptly.

Can a tire be shaved to fix out-of-round?

Shaving is sometimes done to correct radial runout on new tires, but it is a temporary fix and not recommended for general use. Most manufacturers do not approve shaving for out-of-round tires.

How long can I drive on an out-of-round tire?

It is not safe to continue driving on a tire that causes significant vibration. The vibration can be a sign of internal damage, and the tire could fail. Replace it as soon as possible.

Are out-of-round tires covered by warranty?

Most tire warranties cover defects in material and workmanship, which includes out-of-round conditions, if the tire is within the specified mileage and tread depth limits. Check with the manufacturer or your dealer.