Underinflation: Too little air in a tire causes the center to sag inward and experience less contact with the road, leading the edges of the tread to wear down more quickly.
Overinflation: Too much air in a tire causes the center of the tread to bulge outward, where it bears the brunt of road contact and wears down more quickly.
Misaligned wheels: A misaligned wheel focuses friction on one side of the tire, leading it to wear down more quickly.
Wheel balance/suspension: Worn-out suspension parts (usually shocks or struts) or wheel-balance issues allow a tire to bounce in and out of contact with the road, creating "scalloped" grooves.
Issues while driving
Vibrating, humming, or thumping: Such noises can indicate cupping, flat spots on a tire, out-of-balance wheels, or a tire with a separated internal belt.
Pulling to one side: If the car pulls to one side while driving at a steady speed, there may be an underinflated or damaged tire on the side it pulls toward.
Front tires and rear tires handle different amounts of acceleration, steering, and braking wear. For example, the front tires on front-wheel drive cars absorb the brunt of both acceleration and braking, so to prevent the front tires from wearing out long before the rear tires, the front tires must periodically be swapped to the back and the rear tires to the front. (The exact way the tires are rotated usually depends on whether the vehicle is front-, rear-, or all-wheel drive.)
Check your vehicle’s owner’s manual for mileage recommendations; rotation is usually recommended between every 5,000 and 8,000 miles.
Tires depend on grooves in their treads to maintain traction and shed water on wet roads. Depth is measured in 32nds of an inch, with most new tires starting out at 10/32” or 11/32”. Measuring your remaining tread depth is one of the most important car inspections you can do; you should do it monthly to uncover excessive or uneven wear before it becomes a safety hazard.
The easiest and most accurate way to check tread depth is with a dedicated tread depth gauge, available at auto parts stores. But if you have some spare change handy, you can also use a quarter or penny to measure depth.
In many states, it’s illegal to drive on tires with less than 2/32” of tread, so seeing the top of Lincoln’s head means your tires need immediate replacement.
Even tires that pass the penny test may be worth replacing, however. The Tire Rack, America’s largest independent tire tester, found significant performance differences between tires that only passed the penny test and those that passed the quarter test as well. In one test, pickups traveling at 70 mph that only passed the penny test needed 499 feet to stop on wet pavement, while pickups that passed the quarter test needed 377 feet, a 24 percent improvement.
In turn, AAA's own research has found that all-season tires that pass the quarter test exhibit an average increased stopping distance of 87 feet and about a one-third reduction in handling ability compared to new tires. Tested side-by-side at 60 mph, vehicles with worn tires are still going 40 mph when vehicles with new tires have come to a complete stop.
Given these results and others, AAA suggests using the quarter test to determine when it’s time for new tires.
Having the wrong tire pressure leads to uneven wear and lower gas mileage, so you should check your car’s tire pressure at least once a month to make sure it’s at the manufacturer-specified level.
1. If you don’t already have one, get a tire pressure gauge. There are digital, dial, and pen-type varieties, with the digital and dial models generally being easier to use.
2. Check the tires before the vehicle has been driven. Warm tires will give higher readings than tires at rest.
3. Remove the tire’s valve cap, press the gauge over the valve stem, and press firmly until there’s no air hissing out.
4. Note the tire's current pressure on the gauge. Compare it to the pressure specified by the manufacturer, usually found in the owner's manual or in the driver's door jamb.
5. If the pressure is below normal, add air, rechecking with the gauge that way you don't add too much.
6. If the pressure is above normal, or you overfill the tire, release air by pushing on the metal stem in the middle of the valve with a fingernail or pen.
7. Replace the valve cap and repeat for the other tires. If your vehicle has a spare tire, check it as well. Keep in mind that some spares require higher inflation pressure.
Every month, you should:
Every 5,000 to 8,000 miles:
When you get new tires: