How to know which tire has low pressure?

The quick answer is that a Tire Pressure Monitoring System (TPMS) warning alerts you that one or more tires are underinflated, but you’ll need to measure each tire’s pressure with a gauge and compare it to the vehicle’s recommended PSI (usually found on the driver’s door jamb or in the owner’s manual) to identify the exact tire. After a warning, check all tires while they’re cold to confirm which one is low and by how much.

Understanding the warning and what to look for

The TPMS can vary in how it communicates which tire is low. In some cars the system points to a specific tire on the dashboard, while in others you’ll only get a general underinflation alert. Regardless of the system, you should measure each tire with a reliable gauge to identify the low-pressure tire accurately.

Direct vs indirect TPMS

Direct TPMS uses sensors inside each tire to report the actual pressure and can sometimes indicate which tire is low. Indirect TPMS relies on wheel-speed sensors and may only flag “low pressure” without specifying the tire. Even with direct TPMS, confirming the exact tire with a gauge is a best practice.

• If your dashboard indicates a specific tire position (e.g., front left or rear right), note that as a starting clue, but verify with a measurement.


• If the alert doesn’t identify a tire, proceed to measure all four tires (and the spare, if you carry one) with a gauge.


• Look for visual signs of underinflation, such as flattened contact patches, bulging sidewalls, or uneven wear compared with the other tires.


• Check wear patterns to help confirm underinflation history; underinflation often causes more wear along the outer edges or in the center of the tread depending on usage.

By combining the TPMS information with precise pressure readings, you can reliably determine which tire is low and take corrective action.

Step-by-step: test and bring tires to the proper pressure

Prepare to check all tires systematically and adjust to the recommended pressure. The steps below ensure accuracy and safety.

• Find the recommended PSI for your vehicle from the door jamb sticker on the driver’s door or in the owner's manual. Do not inflate to the tire’s maximum sidewall pressure—the recommended value is what you should use for everyday driving.


• Check tires when they are cold, meaning the car hasn’t been driven more than a mile or two recently. If you must check after driving, add 1–2 PSI to account for heat, but verify after the tires cool down.


• Use a reliable tire pressure gauge (digital, dial, or pencil gauge) and measure each tire’s pressure at the valve stem. Remove the valve cap first and replace it securely afterward.


• Inflate each tire to the recommended PSI, starting with the tire that read the lowest on your gauge. Use a pump with an accurate gauge and monitor the pressure as you inflate.


• Recheck all four tires after inflation to confirm they’re at the recommended pressure. Do not forget the spare if you carry one, as it may be used in an emergency.


• Put the valve caps back on and drive briefly, then recheck the pressures again once the tires have cooled to ensure they’ve settled at the correct level.

Regularly checking and maintaining proper tire pressure improves fuel efficiency, handling, and tire life, and reduces the risk of a blowout on the road.

Tips, best practices, and special considerations

Keep these practical tips in mind to maintain correct tire pressure and stay safe in varying conditions.

• Temperature affects tire pressure: in cold weather, pressures drop; in hot weather, they rise. Check pressures when tires are cold for consistency.


• Seasonal changes and load can alter required PSI. If you routinely carry heavy loads or passengers, verify whether you should adjust the target PSI to accommodate the load.


• Run-flat tires and dynamic conditions can complicate readings. Use a quality gauge and follow the vehicle’s guidance for your specific tire type.


• If you notice persistent loss of pressure in a tire (even after inflation), or you see sidewall damage, a slow leak, or punctures, consult a tire professional promptly.

Summary

To determine which tire has low pressure, rely on the TPMS as an alert, then confirm by measuring each tire with a reliable gauge against the manufacturer’s recommended PSI. Inflate low tires to the specified pressure, recheck after they cool, and maintain regular checks to ensure safety, fuel efficiency, and tire longevity.

Is the penny test for tires accurate?

The penny test is a reasonably accurate and quick way to determine if your tires have reached the legal minimum tread depth of 2/322 / 322/32 of an inch. If you can see the top of Lincoln's head when you place a penny upside down in the tread, your tires are worn and should be replaced. While useful, it's less precise than using a tread depth gauge, and many safety experts recommend replacing tires when the tread depth reaches 4/324 / 324/32 of an inch for better performance in wet conditions, a threshold that the quarter test can help you assess.
 
How to perform the penny test

1. Find a penny with President Lincoln's head facing you. 
2. Insert the penny into a tire tread groove with Lincoln's head pointing down. 
3. Check if the top of Lincoln's head is visible. 
4. If you can see the top of his head, your tread depth is 2/322 / 322/32 of an inch or less, and your tires need to be replaced. 
5. If his head is completely covered, you have sufficient tread. 
6. Repeat the test in several spots on each tire to check for uneven wear. 

Why the quarter test is recommended as well

• The space between the top of George Washington's head and the edge of a quarter is approximately 4/324 / 324/32 of an inch. 
• Tires with less than 4/324 / 324/32 of an inch of tread have significantly reduced traction, especially in wet conditions. 
• Performing the quarter test is a proactive way to know when your tires are approaching a dangerous level of wear, rather than waiting until they are bald. 

How do I know which tire is unbalanced?

Imbalanced tires can wobble or hop up and down, causing vibration. If a front tire isn't properly balanced, you'll likely feel vibrations in the steering wheel. If the problem is in the rear, you'll feel shaking in the seat or floor.

How does a car know which tire is low?

Indirect TPMS uses your car's Antilock Braking System (ABS) wheel speed systems. When the pressure in a tire drops, that tire will spin at a different speed, which sends a message to your car's computer system and triggers an indicator light.

How can I tell which tire is bad on my car?

You can tell a tire is bad by checking for shallow or uneven tread, visible cracks or bulges in the sidewall, excessive vibration when driving, or an unusual amount of noise. Regularly inspecting your tires for these signs can help you identify a bad tire before it leads to a more serious problem. 
Visual and tactile inspection

• Shallow or uneven tread: Use the penny test or check for the built-in tread wear indicators. If Lincoln's head is fully visible when the penny is inserted upside down, the tread is too low and the tire needs immediate replacement. 
• Cracks or bulges: Look for any cracks, cuts, scrapes, or blisters on the tire's sidewall or surface. Bulges indicate a compromised internal structure that could lead to a blowout. 
• Uneven wear: Check if the wear pattern is uneven across the tread. This can indicate issues with your car's alignment, suspension, or tire pressure. 

Driving and performance checks

• Vibration: Feel for excessive shaking or wobbling in the steering wheel or through the rest of the vehicle while driving. A steady vibration can be a sign of a bad tire. 
• Noise: Listen for any new or unusual noises, such as a constant humming or flapping sound, which can signal a problem with the tire. 
• Frequent pressure issues: If a tire repeatedly loses air, it may have a slow leak or other damage that requires attention. 
• Poor handling: The vehicle may feel sluggish, pull to one side, or take longer to stop than usual.