Tire Pressure and Tread Depth: How to Check Your Tires at Home
Tires are the only part of your vehicle that touches the road, yet they are one of the most overlooked. Correct pressure and healthy tread improve braking, handling, fuel economy and tire life. The good news is that checking both takes only a few minutes and very simple tools.
Why Tire Pressure Matters
- Under-inflated tires flex more, build up heat, wear on the outer edges and increase rolling resistance, which lowers fuel economy. Severe under-inflation can lead to tire failure.
- Over-inflated tires have a smaller contact patch, which reduces grip and makes the ride harsher. They tend to wear in the center.
- Correctly inflated tires give the best balance of grip, comfort, fuel economy and even wear.
Where to Find the Correct Tire Pressure
Use the pressure listed on the tire placard, usually a sticker on the driver's door jamb, or in your owner's manual. Do not use the number molded on the tire sidewall; that is the maximum pressure the tire can safely hold, not the recommended pressure for your vehicle. Some vehicles list different pressures for front and rear tires or for heavy loads.
How to Check Tire Pressure
- Check when the tires are cold, ideally before driving or after the car has been parked for a few hours. Driving warms the air inside and raises the reading.
- Remove the valve cap and press a tire gauge firmly onto the valve stem.
- Read the pressure and compare it with the placard.
- Add air in short bursts if needed, rechecking as you go. If you overfill, press the center pin of the valve briefly to release air.
- Replace the valve cap, which keeps dirt and moisture out.
- Do not forget the spare tire if your vehicle has one.
Check pressure at least once a month and before long trips. In the Heber Valley, check more often in fall and winter, because tire pressure drops roughly one to two psi for every 10°F drop in outside temperature.
What About the TPMS Light?
Vehicles sold in the United States since the 2008 model year are required to have a tire pressure monitoring system (TPMS). The warning light, which looks like a horseshoe with an exclamation point, turns on when one or more tires is significantly under-inflated. A steady light means check your tires; a flashing light that then stays on usually means the system itself has a fault.
TPMS is a helpful safety net, but it is not a substitute for regular checks. The light often does not come on until a tire is already well below the recommended pressure.
Understanding Tread Depth
Tread depth is measured in 32nds of an inch. Many new passenger tires start at around 10/32" to 11/32". Most states, including Utah, treat 2/32" as the minimum legal tread depth, but tires lose much of their wet and snow traction well before that point. Many experts recommend considering replacement around 4/32" for wet roads and around 5/32" to 6/32" if you regularly drive in snow.
The Penny Test and the Quarter Test
You do not need a special gauge to get a quick idea of tread depth:
- Penny test: insert a penny into a tread groove with Lincoln's head upside down and facing you. If you can see the top of his head, the tread is at or below 2/32" and the tire should be replaced.
- Quarter test: insert a quarter with Washington's head upside down. If you can see the top of his head, the tread is about 4/32" or less, and it is time to start shopping for tires, especially before winter.
Check several spots across each tire: the inner, center and outer grooves. Most tires also have tread wear indicator bars molded into the grooves. When the tread is level with these bars, the tire is worn out.
Reading Wear Patterns
| Wear pattern | Possible cause |
|---|---|
| Both outer edges worn | Under-inflation |
| Center worn | Over-inflation |
| One edge worn | Alignment (camber or toe) |
| Feathered or saw-tooth tread | Alignment (toe) |
| Cupping or scalloped patches | Worn suspension parts or imbalance |
If you see uneven wear, read signs your car needs a wheel alignment. Fixing the cause protects your next set of tires.
Check Tire Age, Too
Rubber ages even when a tire has plenty of tread. Look for the DOT code on the sidewall; the last four digits show the week and year of manufacture. For example, "2421" means the 24th week of 2021. Recommendations vary by manufacturer, but many suggest having tires inspected annually after about six years and replacing them by about ten years regardless of tread. Cracks in the sidewall or between tread blocks are a sign of aging.
Other Things to Look For
- Nails, screws or other objects in the tread
- Bulges or bubbles on the sidewall, which mean internal damage and require replacement
- Cuts or gouges in the sidewall
- A tire that keeps losing air, which may have a slow leak at the puncture, bead or valve
Many punctures in the tread area can be repaired properly with a plug and patch, but damage to the sidewall or shoulder generally cannot. If a tire goes flat on the road, see our roadside safety guide.
Rotate Your Tires
Front and rear tires wear differently. Rotating them at the interval your manufacturer recommends, often every 5,000 to 7,500 miles, helps them wear evenly and last longer. Many drivers rotate tires at every oil change.
Tire help in Heber City: Tracy's Auto Repair offers flat tire repair, winter/summer tire changes and wheel alignment. Our signature semi-synthetic oil change includes a free tire rotation and balance. Book online.
Conclusion
Once a month, check pressure with a gauge and look at your tread with a penny or quarter. Watch for uneven wear, damage and aging rubber. These small habits keep you safer on wet and snowy roads and help your tires last as long as they should.
Frequently Asked Questions
Should I use nitrogen instead of air in my tires?
Nitrogen may leak slightly more slowly than regular air, but regular air works well for everyday driving. The most important thing is checking pressure regularly and keeping it at the recommended level.
Why does my TPMS light come on in the morning and go off later?
Cold overnight temperatures lower tire pressure. As you drive, the tires warm up and pressure rises, turning the light off. Add air to bring the cold pressure back to the recommended level.
Can I replace just one or two tires?
Sometimes, but it depends on the tread depth of the remaining tires and your drivetrain. Many all-wheel-drive vehicles require all four tires to have very similar tread depth. Replacing in pairs on the same axle is the minimum.
How long does a tire plug and patch last?
A proper repair from the inside of the tire, using a plug to fill the puncture and a patch to seal the inner liner, is designed to be permanent for punctures in the repairable tread area.