Longer-lasting tires make safety checks more critical than ever. While yesterday's tires typically wore out in 30,000 miles or less, many of today's are warranted for two to three times that mileage. That means they may still have lots of tread even though heat, the environment, and potholes may have weakened them.
Underinflated tires can also get hot and weaken, increasing the chance of a blowout. A 10° F drop in outside temperature lowers pressure by about 1 pound per square inch. What's more, all tires tend to leak over time. Pressure loss averaged 6 psi for 36 all-season models we checked after one year.
To help keep your tires safe:
- Check the air pressure each month when the tires are cold (before they've been driven more than a couple of miles). Be sure that they're inflated to the air pressures listed on the placard on the doorjamb or inside the glove compartment or fuel-filler door.
- Look for cracks, cuts, or bulges in the sidewall or tread and replace tires that have them.
- Check for uneven tread wear, which typically denotes poor wheel alignment or worn suspension components, and have both checked by a shop. Also have your vehicle's alignment and suspension checked before mounting new tires to prevent them from wearing prematurely.
- Stay within the vehicle's weight capacity listed on the doorjamb placard. Overloading makes tires run hotter, increasing the chance of a failure.
- It used to take a penny to check the tread depth of your tire. We're suggesting it should really take a quarter.
It has long been the standard that tires are worn out when their tread depth reaches 1/16 inch (or 2/32 inch as found on standardized tread-depth gauges). The easiest way to measure this, if you didn't have a gauge, was to hold a penny upside down in the tread. If the top of Lincoln's head was visible, you needed new tires. See test results of foul weather comprises with worn-out tires.
But CR's tests show that using a penny is too stingy and that most consumers should consider replacing their tires when the tread reaches 1/8 inch.
To get a handle on how much tread depth makes a difference, we tested two models of V-rated performance all-season tires, a kind widely available on new cars. We subjected sets with full tread, 1/8 inch, and 1/16 inch to our standard battery of tests. Tires were shaved to simulate a worn condition, although the effects of tires' aging could not be taken into account.
Though performance on dry pavement actually improved a bit, the 1/8-inch tread was notably worse in hydroplaning resistance and in snow. By the time only 1/16 inch remained, wet-pavement cornering and braking had also dropped. This suggests that when your tires have less than 1/8 inch of tread left, it's a good time to start shopping for replacement tires.