Tires: pressure, tread, age, rotation and replacement

Set pressure from the door placard, read tread against the lines different sources draw, find each tire's age in its DOT code, and know what the warning light does and does not tell you.

Pressure: the placard, cold tires and a monthly check Understand

Tire pressure is the one tire check every owner's manual leaves to the owner, and the one with the clearest sources. Three questions settle it: which number, measured when, and how often.

Which number: the placard, not the sidewall

Your car's recommended pressures are printed on the tire placard, the Tire and Loading Information label on the driver's door edge or door post, and in the owner's manual. NHTSA, the federal vehicle safety agency, says to use that label, not the number on the tire itself (NHTSA, Tires). The number molded on the sidewall is the maximum pressure: in NHTSA's winter guidance, the most the tire can hold, not what your car wants (NHTSA, Winter Weather Driving Tips). fueleconomy.gov, run by the Department of Energy and EPA, says the same: use the door-jamb pressure and do not use the maximum printed on the sidewall (fueleconomy.gov, Keeping Your Vehicle in Shape). Convention

The placard often gives different front and rear figures, and a separate figure for the spare. It also gives the original tire size (for example a code such as 215/55R17), the load index (a number standing for how much weight the tire is rated to carry) and the speed rating (a letter for the top speed it is rated for). Copy all of it to the car facts sheet; you need the size and load figures when you buy tires (buying tires).

Pressures are given in psi, pounds per square inch, and often also in kPa. A compact spare can be very different from the road tires: the 2025 Kia Sorento's owner's manual sets its compact spare at 60 psi (Kia, 2025 Sorento owner's manual: compact spare). That is one model's figure. Product-specific Your spare's figure is on your placard or in your manual.

When: cold

A tire's pressure rises as it warms up from driving, so the placard figure is a cold figure. NHTSA defines cold as a tire that has "not been driven on for at least three hours"; the U.S. Tire Manufacturers Association (USTMA), the tire makers' trade group, says parked for at least three hours (USTMA, Tire Care Essentials). First thing in the morning, before you drive, is the easy time. Physical principle

If you have to add air when the tires are warm, at a gas station after a drive, NHTSA says to fill to the cold placard pressure and recheck once the tires are cold. Slightly low beats significantly low.

Outside temperature moves the reading too. USTMA puts it at one to two psi for every 10 degrees of temperature change. A tire set correctly on a warm October afternoon can read several psi low on a cold December morning, which is why NHTSA's winter page lists a pressure check among its winter steps. Physical principle

How often: monthly, spare included

NHTSA and USTMA both say to check at least once a month and to include the spare. USTMA adds a check before a long trip, a heavy load or towing. NHTSA suggests keeping a tire pressure gauge (a small hand gauge that reads the pressure at the valve) in the car. Your own gauge means the same instrument every month. Put "tire pressure, monthly" on the schedule sheet; the sheet already has a row for it. Convention

What pressure does for you, by the sources' own measures: fueleconomy.gov estimates that keeping tires at the recommended pressure improves gas mileage by about 0.6 percent on average and up to 3 percent in some cases, and that mileage falls about 0.2 percent for every 1 psi drop in the average of all four tires. Those figures assume an average under-inflation of 10 percent across the tires. The safety reasons are in the next sections: low pressure is one of the causes of the irregular wear and damage NHTSA lists as reasons to stop using a tire.

The low tire pressure light (TPMS)

A tire pressure monitoring system (TPMS) watches the tires and lights a yellow warning on the dash when one is low. NHTSA says it has been required on all passenger cars, light trucks and vans from model year 2008, and that some 2006 and 2007 models have it.

The federal standard sets when the light must come on. Under FMVSS 138, the TPMS light has to come on within 20 minutes once a tire is 25 percent below the maker's recommended cold pressure, or below a floor set in the standard's table, whichever is higher (49 CFR 571.138, FMVSS 138). On a car whose placard says 35 psi, 25 percent below is about 26 psi, unless the table's floor is higher. So the light can stay off while a tire runs well under the placard figure.

• Light on and steady: NHTSA says at least one tire is significantly under-inflated. Check all the tires with your gauge as soon as you safely can.
• Light on during a cold morning, off after driving: NHTSA says it can do that. The tire is low when cold, which is when the placard figure applies; check and set it cold.
• Light flashes for about a minute, then stays on: NHTSA says a flash of 60 to 90 seconds followed by a steady light means the system itself has a malfunction, so it may not warn you of low pressure. See the dealer or a shop.

USTMA says the warning comes at 25 percent under-inflation and "may be too late to prevent damage," and that TPMS does not replace monthly checks. NHTSA says the system is not meant as a substitute for regular tire maintenance. Two sources, one point: the light is a backstop, and the gauge is the check. Convention What every dash light means, and which ones mean stop, is in Warning lights and codes and the warning lights table.

Tread depth: measure it and write it down

Tread depth is the depth of the grooves in the tread, measured from the top of the tread to the bottom of a main groove. In the US it is given in 32nds of an inch. Consumer Reports, the nonprofit testing organization, says all-season tires typically start at 10/32 to 11/32 in. (Consumer Reports, worn tires and wet traction). The grooves carry water out from under the tire, so as they get shallower, grip on wet and snowy roads falls. Continental, a tire maker, says wet and snow braking decline progressively as tread wears (Continental, Replacing tires). Physical principle

How it is read

• A tread depth gauge. A tread depth gauge is a small probe that you press into a groove; it reads in 32nds (and often millimeters). It gives a number you can write down and compare next time. It is this chapter's default.
• Wear bars. A tread wear indicator, or wear bar, is a raised bar molded across the bottom of the grooves. USTMA's care manual says the bars appear at 2/32 in. (USTMA, Care and Service of Passenger and Light Truck Tires), and Michelin puts its wear indicators at 2/32 in. (1.6 mm) (Michelin, When Do I Need New Tires?). When the tread is level with a bar, the tire is at that line.
• A penny and a quarter, as rough gauges. With a penny upside down in a groove, seeing the top of Lincoln's head means about 2/32 in. is left; with a quarter, seeing all of Washington's head means about 4/32 in. (NHTSA; Consumer Reports). A coin tells you which side of a line you are on, roughly. It gives no number to log, so use it between gauge readings, not instead of them. Test it

Measure each tire in more than one groove, across the width (inner, center and outer), and write the lowest reading by position: left front, right front, left rear, right rear, spare. Writing it by position is this manual's convention; it lets you see uneven wear and compare one visit with the next. This manual's convention The recommendations sheet has a "what they saw" column for a shop's readings, and the same format works for your own.

The lines, and what each one is for

Sources draw different lines, and they mean different things. Here is the short version; the full side-by-side, with who says what, is in Tires in depth.

2/32 in., worn out. NHTSA says tires at 2/32 in. "are not safe and should be replaced"; USTMA's care manual says to replace tires worn to 2/32 in. anywhere on the tread face; USTMA's consumer page says 2/32 is the time to go to a tire shop. Where the agency and the tire makers agree, this is the line that ends a tire's use. Convention

4/32 in., start shopping. AAA tested all-season tires worn to 4/32 in. against new ones. On wet pavement, the worn tires needed on average an additional 87 feet to stop a passenger car, 43 percent farther, and handling fell by a third (AAA, Tread Lightly, June 2018). In stops from 60 mph, at the point where the cars on new tires had stopped, the cars on worn tires were still going about 40 mph. AAA's report recommends that drivers "begin shopping" for replacements at 4/32 (AAA, All-Season Tire Testing report), and Consumer Reports says the same with the quarter test. AAA wore its test tires artificially, which it calls a best case with no aging effects. Test it

Your own tires. The tire's maker can say more for its own product than any general line, and your owner's manual may add the car maker's view. Michelin's page, for example, says to follow the vehicle maker's replacement advice for the tires that came on a new car. Product-specific

So the default here is plain: measure, write the depth down by position, and plan with the shop. At 4/32 in., start comparing written quotes, as Priya does in See it; at 2/32 in., the tire is done by NHTSA's and the tire makers' measure. Between those lines, how soon you replace is your call, with your tire maker's guidance, your roads and the shop's reading of the tire in front of it.

State minimums vary

Each state sets its own legal tread minimum, if it sets one, and the figures differ. AAA's report says most states that require periodic inspections mandate replacement at 2/32 in. California's Vehicle Code, as one example, bars using a tire with less than 1/32 in. of tread in any two adjacent grooves, requires 6/32 in. on snow tires used in place of chains where traction controls are posted, and bars dealers from selling or installing tires below those depths (California Vehicle Code section 27465). The only federal tread minimum we found applies to buses and trucks, not passenger cars (Tires in depth). A legal minimum is a floor, not a target: California's 1/32 in. is half of NHTSA's worn-out line. For your own state's rule, ask your state's motor vehicle agency or its inspection program. Ask the authority

Damage and uneven wear

Depth is one reason to stop using a tire; damage is another. NHTSA lists cuts, cracks, bulges, and irregular wear from under-inflation or overload as reasons to stop using a tire. Ford's tire page lists bulges, groove cracking, cuts, sudden pressure loss, pulling and sudden vibration as reasons to have tires inspected (Ford, How often should I replace the tires on my Ford?). Michelin says sidewall damage is not repairable. Whether a damaged tire can be repaired is a question for a tire professional who has the tire in front of them.

Tire age: reading the DOT date code

NHTSA says you cannot detect tire aging by looking at the tire, and names the tires most at risk from it: those on low-mileage cars, collector cars and RVs, and tires that sit in sunlight or warm climates. Its risk list is a reason age matters even for a tire that is rarely driven, and the age is printed on the tire.

Reading the code

Every tire sold in the US carries a DOT code, also called the tire identification number (TIN): a string that starts with the letters DOT and runs 12 or 13 characters (USTMA, Tire Registration). The last four digits are the date code: two for the week, two for the year. NHTSA's example is 0308, the third week of 2008; Michelin's is 3520, week 35 of 2020. The federal rule defines week "01" as the first full calendar week of the year, Sunday to Saturday (49 CFR 574.5). Convention

The same rule requires the full code on one sidewall only, so it may face in toward the car. NHTSA says to look on both sides. A flashlight helps on the outer side; for an inner sidewall, ask the shop to read it at your next visit rather than crawling under the car. Type each tire's four digits, spare included, into the tire age calculator, which gives the week, the year and the age today, and write the dates on the car facts sheet by position.

How old is too old: follow your tire maker and your car maker

No federal rule sets a tire's age limit, and the tire makers and car makers we read do not agree on one. This manual does not set a default age. Read the guidance from the company that made your tires, and from your car's maker in your owner's manual, and follow it. Product-specific

Across the six, none says a tire is safe or unsafe on its age alone, and Michelin, USTMA and Ford's second page all send older tires to a professional for inspection. Where your tire maker and your car maker give different ages, ask the tire maker's customer line or the shop which one applies to the tires on your car; Michelin's own page, for instance, defers to the car maker for original tires. Ask the authority Why the two Ford pages differ, and what USTMA's position means for the others, is in Tires in depth.

The spare

The spare ages on the same clock as the road tires and is the one most often forgotten. Michelin, Continental and Ford include spares in their age guidance; NHTSA and USTMA include them in the monthly pressure check; Ford's second page says to inspect it even if unused. A compact spare (a temporary, smaller spare) has its own limits: the 2025 Kia Sorento's manual, for example, says not to drive on it over 50 mph and to replace it with a proper tire at the first opportunity. NHTSA says not to use a full-size spare to replace worn tires except in an emergency. Write the spare's pressure figure and DOT date on the car facts sheet with the others. Product-specific

Rotation, alignment and buying tires

Rotation: your manual's interval

Rotation means moving each tire to a different position on the car, in a pattern the maker sets, so the tires wear more evenly. The interval comes from your owner's manual or maintenance schedule. Three examples show how widely they differ:

• The 2025 Hyundai Sonata's normal schedule rotates the tires every 8,000 miles or 12 months (Hyundai, 2025 Sonata normal maintenance schedule).
• Tesla's maintenance page rotates every 6,250 miles, or sooner if the tread depths differ by 2/32 in. or more (Tesla, Vehicle Maintenance).
• Honda's Maintenance Minder shows code 1 when rotation is due, instead of a fixed mileage (Honda Canada, Maintenance Minder schedule).

Where the maker recommends rotation but you cannot find an interval, NHTSA and USTMA both give every 5,000 to 8,000 miles, and NHTSA adds sooner if wear is uneven. NHTSA also says rotation is not recommended for some vehicles, and that different front and rear tire sizes may prevent it. Your manual decides; the generic figure is only a fallback. Product-specific Copy your interval, in miles and months, onto the rotation row of the schedule sheet, with the manual page as the source. Electric cars have their own rotation figures, covered in Hybrids and electric cars.

Alignment and balancing

Alignment is the setting of the angles at which the wheels meet the road. NHTSA says correct alignment keeps a car from veering on a straight road, and USTMA says to have it checked at signs such as pulling. Balancing adds small weights to a wheel so it spins without vibrating; NHTSA says new tires should be balanced when installed. Alignment is usually an inspection item or a response to a symptom rather than a fixed interval; check your schedule. A pull or a vibration goes on the symptom log with when it happens, as Sounds, smells, leaks and feel describes.

Buying tires: size, load and where the new pair goes

USTMA says to match the size, load index and speed rating recommended by the vehicle maker or the tire maker, and not to go smaller or lower in load capacity (USTMA, Replacing Your Tires?). Those figures are on the placard you copied. When two shops quote, check that both quote the same size and load; the estimates sheet keeps quotes side by side, and Reading a repair estimate covers reading each line.

USTMA recommends replacing all four tires at once. If you replace only two, USTMA says the new pair goes on the rear axle, for wet grip and to resist oversteer, and Ford's tire page says the newest go on the rear as well. Placement on your car is the installer's job, with your car maker's guidance; ask where the new pair will go and why. Ask the authority

Register the tires

Tire registration links a tire's DOT code to your name and address so its maker can reach you if the tire is recalled. USTMA says makers use it to contact you in the event of a recall. Federal rules require the registration form to tell you that the maker can reach you about a recall only if it has your name and address. They require an independent dealer to give you a form with the full DOT code and the dealer's name filled in, or to register the tires for you at no charge within 30 days of the sale, or to do it electronically (49 CFR part 574). USTMA's recall checker searches by DOT code, for its member companies only (USTMA, Tire Recalls). A recalled tire's free remedy has a 180-day window and an age limit; both are in Recalls, warranties and service contracts.

See it: Priya's front tires See it

Priya's tire line goes on the recommendations sheet as "not now, buy within two months" with the depth and the two quotes. How she decides on the rest of the list (brake pads at 3 mm, brake fluid, coolant, a fuel injection service) is in Discussing recommendations; the brake measurements are in Brakes, battery, wipers and lights.

• NHTSA, Tires: the placard, cold pressure, the penny test, TPMS and reading the DOT date.
• AAA, Tread Lightly: the wet-braking test of tires at 4/32 in. against new ones.
• USTMA, Tire Care Essentials: the tire makers' monthly checks, wear bars and rotation fallback.
• Michelin, When Do I Need New Tires?: one tire maker's age and tread guidance, with a worked DOT date.

Practice: pressure, tread and dates Practice

Minimum: the placard pressures and tire size on the car facts sheet, all five tires checked cold and set to the placard, each tire's DOT date (or "ask the shop" for an inner sidewall), and a monthly pressure row and the rotation interval on the schedule sheet. Time: about 30 minutes, after the car has been parked for at least three hours. Materials: a tire pressure gauge, a tread depth gauge (a penny and a quarter if you have no gauge yet), a flashlight, access to air (a home inflator or a gas station), your owner's manual, and the car facts, schedule and recommendations sheets (or paper).

Work with the car parked on level ground, in park with the parking brake set, out of traffic. Nothing in this practice needs a jack or a tire off the car.

1. Read the placard. Open the driver's door and find the Tire and Loading Information label on the door edge or post. Write the front, rear and spare pressures, the tire size, the load index and the speed rating on the car facts sheet. If the label is missing or unreadable, use the owner's manual's tire section.
2. Check each tire cold. Remove a valve cap, press the gauge on squarely, read it, and write the reading by position. Do all four and the spare. Then add or let out air to reach the placard figure, recheck, and put the caps back.
3. Measure the tread. On each tire, read the gauge in an inner, a center and an outer groove, and write the lowest by position on the recommendations sheet with the date. Note any tire whose readings differ across its width. If a wear bar is level with the tread, write that.
4. Look, without touching anything sharp. Walk around each tire with the flashlight and note bulges, cuts, cracks or anything stuck in the tread. Do not pull out a nail or screw; write where it is and show the shop.
5. Read the DOT dates. Find the code starting "DOT" on each sidewall you can see, and read its last four digits. Type them into the tire age calculator and write each date by position on the car facts sheet. For a code facing inward, write "ask the shop."
6. Fill in the schedule. Add "tire pressure, monthly" and the rotation interval from your manual, with the page, to the schedule sheet.

Your car Your car

Check your work Check your work

Criteria

• Does the car facts sheet have the placard pressures (front, rear, spare), the tire size, load index and speed rating, and where they came from?
• Were the pressures read cold, with your own gauge, on all four tires and the spare, and set to the placard rather than the sidewall?
• Is each tire's tread depth written down by position with a date, as a gauge reading where you have one?
• Does each tire have a DOT date, or "ask the shop" for one you could not read?
• Does the schedule sheet have a monthly pressure check and your manual's rotation interval, with its source?
• If any tire is near a line, is the next step written as a question for the shop or a plan with a date, not as a verdict?

Worked example

Priya's sheets read: placard pressures and size copied from the door label; pressures checked cold one morning and set; front tires 4/32 in. by the shop's gauge, rears "ask at next visit"; two DOT dates read from the outer sidewalls and two marked "ask the shop"; rotation interval from her online manual on the schedule sheet; the tires on the recommendations sheet as "not now, buy within two months," with two written quotes on the estimates sheet. It passes. It does not say the front tires are safe for two months; it says the plan holds under the assumption of no damage, and the shop's look at the tires settles that.

Common mistakes

• Inflating to the sidewall number. That is the tire's maximum. The placard figure is the one for your car.
• Checking after a drive. Warm tires read high. Check cold, or fill to the placard and recheck cold later, as NHTSA says.
• Waiting for the TPMS light. It comes on at about 25 percent low, and USTMA says that may be too late to prevent damage.
• Reading a coin as a measurement. The penny and quarter tell you roughly which side of 2/32 or 4/32 you are on, and nothing to log.
• Treating one age figure as a rule. Six years is one Ford page; ten is Michelin's and Continental's; USTMA knows of no data for any fixed life. Your tire maker's guidance governs your tires.
• Forgetting the spare. It needs the monthly pressure check and has a DOT date like the others.

What is still unresolved

Whether a particular tire is fit to keep is settled by a tire professional looking at it. Your state's legal tread minimum is settled by your state's motor vehicle agency. Which age guidance applies when your tire maker and car maker differ is settled by asking them or the shop. Whether to buy two tires or four, and from which quote, is your decision; Discussing recommendations and Reading a repair estimate carry the method. Tire recalls and their 180-day window are in Recalls, warranties and service contracts, and an electric car's rotation figures are in Hybrids and electric cars.

Knowledge check and scenario

Checklist

• The car facts sheet has the placard pressures, the tire size and each tire's DOT date, and the schedule sheet has a monthly pressure check and the rotation interval.
• I checked all four tires and the spare cold with my own gauge and set them to the placard.
• Each tire's tread depth is written down by position, with the date.
• I typed each DOT date into the tire age calculator and know whose age guidance applies to my tires.
• I looked up my tire maker's own age and tread guidance and wrote it on the car facts sheet. (Go deeper; optional)
• I rechecked the pressures in a colder or warmer season and compared the readings. (Go deeper; optional)