Tires are the only part of the car that touches the road, and almost everything else, from braking to steering to stability control, depends on them. Yet they are easy to forget because they wear slowly. Here is what to check and when.
Replace tires when the tread is down to 2/32 of an inch (the legal minimum in most US states), or sooner at around 4/32 if you drive in rain or snow often, or when they are about six years old and showing their age.
Tread depth: the numbers
Tread depth in the US is measured in 32nds of an inch. A new passenger car tire usually starts at about 10/32 to 11/32. NHTSA says tires are no longer safe once they are worn down to 2/32.
That is the floor, not the target. Shallow tread cannot push water out of the way, so the tire starts to float on wet roads. AAA research found that hydroplaning risk rises once tread drops under about 4/32, and snow traction suffers below about 6/32. If you drive in wet or wintry weather, budget for new tires before you reach the legal minimum.
Three ways to check tread
- Treadwear bars. Molded into the grooves are small raised bars. When the tread is worn flush with them, the tire is at 2/32 and done.
- The penny test. Put a penny into a groove with Lincoln’s head upside down. If you can see the top of his head, the tread is at or below 2/32.
- A tread depth gauge. It costs a few dollars at any parts store and gives you an actual number. Measure the inner, middle and outer grooves.
Measure more than one spot. If the inside edge is much more worn than the outside, or the middle more than the edges, that points to alignment or pressure problems that will eat the next set too.
How old are your tires?
Rubber hardens and cracks with age, even on a tire with plenty of tread. A car that is not driven much, or a spare that has never touched the road, can have old tires that look new.
The age is printed on the sidewall at the end of the DOT code: the last four digits are the week and year it was made. 2321 means the 23rd week of 2021. NHTSA notes that some tire manufacturers recommend replacing tires after 6 to 10 years regardless of tread. A common rule is to have them inspected from year six and to replace them by year ten no matter what.
Pressure: the free maintenance
Underinflated tires wear faster at the edges, run hotter and cost fuel. Check pressure about once a month and before long trips, when the tires are cold. Use the pressure on the placard on the driver’s door jamb or in the owner’s manual, not the maximum printed on the tire itself.
Rotation
Front and rear tires wear differently, especially on front-wheel-drive cars. Moving them around evens out the wear so all four last longer and can be replaced together. A common interval is every 5,000 to 7,500 miles, which many people line up with every oil change or every other one. Your manual gives the exact interval and the right pattern.
Other reasons to replace a tire now
- A bulge or blister on the sidewall
- Cuts or cracks deep enough to catch a fingernail
- A puncture in the sidewall or shoulder (only tread punctures can be repaired properly)
- A vibration that balancing does not cure
Keeping track
Log the date and mileage when you buy tires and each time they are rotated. Then you know their age without reading sidewalls, and you can see whether a set is wearing out faster than it should. In Badger, tires sit in the same maintenance schedule as everything else, so rotation and replacement show up when they are due.
Common questions
Do I have to replace all four tires at once?
Not always, but tires on the same axle should match. Many all-wheel-drive cars need all four to be close in tread depth, so check your manual before replacing just one or two.
Are new tires better on the front or the back?
Tire makers generally recommend putting the newer pair on the rear axle, whichever wheels drive the car, because grip at the back helps prevent a spin on wet roads.
How long do tires last in miles?
It depends on the tire, the car and how you drive. Many all-season tires carry a treadwear warranty of 40,000 to 80,000 miles. Age can end a tire’s life before the tread does.
