How Long Do Tires Last? The Sidewall Number Is Not a Mileage, and the Legal Floor Is Not a Safety Line

On 23 August 2026 I pulled the first twenty organic results for how long do tires last and for uneven tire wear in the United States, downloaded the pages, and read the bodies. Thirty-four organic results came back across the two searches. Not one of them is a government source.

Here is what they are instead.

What the result is	Slots (of 34)
Sells tires or tire service	10
Manufactures tires, suspension parts or tire-shop equipment	8
Car dealership blog	7
Forum, video or social post	5
Insurance company	2
Independent editorial testing	2
Government	0

Twenty-five of the thirty-four belong to a business whose revenue depends on the answer. That is not an accusation of dishonesty — some of those pages are careful and I quote two of them below. It is a statement about what is missing.

Twenty of the thirty-four served a readable page to a plain fetch; the other fourteen returned 403, 502 or nothing, and I make no claim about what is on them. Of the twenty I could read:

• zero contain the string “CFR”, in any form;
• zero mention FMVSS, or Standard No. 139, or Part 570, or Part 393;
• zero contain “one sixteenth” or “1/16”, which is the depth the wear bars in your tires are actually molded to;
• zero contain “1/32”, which is the legal minimum tread depth in the most populous state in the country;
• two contain the string “UTQG”, and in both cases it is a navigation link to another page, not a sentence on this one.

So the twenty pages that will tell you how long a tire lasts contain no reference to the regulation that grades tire wear, no reference to the standard that puts the wear bars there, and no reference to the statute that decides when your tire becomes illegal. The number they mostly repeat — 2/32 of an inch — turns out to be, in the federal government’s own words, a criterion that “does not in itself impose requirements on any person.”

This piece is the other version. Everything below comes from the Code of Federal Regulations, from three state statutes I read directly, and from one federal traffic dataset. Where a manufacturer or an independent tester is the better source, I say so and quote them.

The number stamped on your sidewall is not a number of miles

Look at the outer sidewall of almost any passenger car tire sold in the United States and you will find three markings: TREADWEAR, then a number; TRACTION, then a letter; TEMPERATURE, then a letter. Almost everybody reads the first one as a mileage promise. It is not one, and the regulation that creates it is unusually blunt about that.

The system is Uniform Tire Quality Grading, 49 CFR 575.104. The treadwear grade is defined there, in the exact words that the regulation requires to be printed on the label sold with the tire:

“The treadwear grade is a comparative rating based on the wear rate of the tire when tested under controlled conditions on a specified government test course. For example, a tire graded 150 would wear one and one-half (1 1/2) times as well on the government course as a tire graded 100.”

Comparative. Against a reference tire graded 100. On one specific course. And then, in the same mandated text:

“The relative performance of tires depends upon the actual conditions of their use, however, and may depart significantly from the norm due to variations in driving habits, service practices and differences in road characteristics and climate.”

How far a tire is actually driven to earn that number

This is the part that is worth knowing, because it changes what the grade means.

The course is real and it has an address. Section 575.104(e)(1)(i) says tire treadwear “is evaluated on a specific roadway course approximately 400 miles in length, which is established by the NHTSA both for its own compliance testing and for that of regulated persons.” Appendix A describes it as “three loops of a total of 400 miles.” The regulation’s note to paragraph (e)(2)(ix)(C) names it: the agency runs its reference tires “for 16 circuits over the San Angelo, Texas, UTQGS test route 4 times per year.”

The candidate tires are broken in for “two circuits of the test roadway (800 miles).” Then, section 575.104(e)(2)(viii): “Drive the convoy on the test roadway for 16 circuits (approximately 6,400 miles).”

That is the whole of it. A treadwear grade is earned over 6,400 graded miles, after 800 miles of break-in — 7,200 miles of driving in total, all of it in west Texas, in a convoy of cars driven nose to tail.

	Miles
Break-in, 2 circuits	800
Graded phase, 16 circuits	6,400
Total driven	7,200
Same distance, as a share of a 60,000-mile treadwear warranty	10.7%
Same distance, as months of average U.S. driving	7.0 months

The last two rows use the only official figure for how much an American vehicle is driven: the Federal Highway Administration’s Table VM-1 for 2023 puts the average at 11,026 miles per year for light-duty short-wheelbase vehicles, across 197,134,299 of them.

The grade is then extrapolated. The regulation instructs the tester to fit a line through the tread-depth measurements and “determine the slope (m) of the tire’s wear in mils of tread depth per 1,000 miles“, correct it against the reference tires run in the same convoy, and then — section 575.104(e)(2)(ix)(F) — “round off the percentage to the nearest lower 20-point increment.”

So a tire graded 500 and a tire graded 519 carry the same number. And the number itself is a projection from about seven months of one kind of driving, on one road, in one climate. It is a genuinely useful comparison between two tires. It is not a forecast of your car.

And the traction letter excludes the thing tread is for

While you are reading the sidewall: the traction grade is measured by towing a test trailer at 40 mph on a wetted surface, locking one wheel, and recording the friction coefficient “between 0.5 and 1.5 seconds after lockup.” The tires are broken in for 200 miles first, so they are essentially new.

And the regulation requires this warning to be printed alongside the grade:

“The traction grade assigned to this tire is based on straight-ahead braking traction tests, and does not include acceleration, cornering, hydroplaning, or peak traction characteristics.”

Hydroplaning is the single failure mode that tread depth exists to prevent. The one letter on the sidewall that says “traction” tells you, by law, that it did not measure it.

What “worn out” means legally, and why there is no single number

Almost every page on this topic says the same thing: the minimum is 2/32 of an inch, and the Department of Transportation says so. The first half is roughly right in most places. The second half is wrong in an interesting way.

The federal 2/32 lives in 49 CFR 570.9(a): “The tread on each tire shall be not less than two thirty-seconds of an inch deep.” That is the complete federal in-use standard for tread depth. The whole of section 570.9 — tread depth, tire matching, general condition, damage, with inspection procedures for each — is 236 words long, heading included, and it was last amended in 1974.

But Part 570 says of itself, at section 570.3:

“This part does not in itself impose requirements on any person. It is intended to be implemented by States through the highway safety program standards issued under the Highway Safety Act (23 U.S.C. 402)…”

Its purpose, per section 570.2, is “to establish criteria for the inspection of motor vehicles by State inspection systems.” It is a yardstick offered to states. What makes your tire illegal is your state’s own vehicle code — and the states do not agree.

Three states, read directly

Jurisdiction	Minimum tread depth for a passenger car	Source
Federal criterion for state inspections	2/32 in	49 CFR 570.9(a)
Virginia	2/32 in, in two adjacent major grooves at three equally spaced intervals	Va. Code § 46.2-1043(A)(1)
Washington	2/32 in, in any two major tread grooves at three locations	RCW 46.37.425
California	1/32 in, in any two adjacent grooves	Cal. Veh. Code § 27465(b)(1)

California’s statute is worth reading in full, because the same section sets three different numbers:

• § 27465(b)(1) — the everyday case: “One thirty-second (1/32) of an inch tread depth in any two adjacent grooves at any location of the tire.”
• § 27465(b)(2) — commercial vehicles: “Four thirty-second (4/32) of an inch tread depth at all points in all major grooves on a tire on the steering axle” of a vehicle listed in section 34500, “and two thirty-second (2/32) of an inch tread depth” on the other axles.
• § 27465(b)(3) — snow tires used instead of chains in a posted control area: “Six thirty-second (6/32) of an inch tread depth at all points in all major grooves.”

One statute, one state, and a six-fold spread between the legal floor for your commute and the legal floor for a snow tire in a chain-control zone.

And the federal government requires twice as much on a truck

49 CFR 393.75(b): “Any tire on the front wheels of a bus, truck, or truck tractor shall have a tread groove pattern depth of at least 4/32 of an inch when measured at any point on a major tread groove.” Paragraph (c) sets 2/32 for everything else on those vehicles.

Line the numbers up and the picture is not subtle:

Vehicle and position	Legal minimum
Front wheels of a truck, bus or truck tractor (federal)	4/32 in
All other truck positions (federal)	2/32 in
Passenger car, Virginia and Washington	2/32 in
Passenger car, California	1/32 in

The front tire of an eighteen-wheeler is required to carry four times the tread that a car tire in California is required to carry. The truck is heavier and its steering failure is more catastrophic — that is the reasoning, and it is sound. But the number on your own car is not a safety threshold that engineering arrived at. It is the point at which a state decided to write a citation.

The wear bars are a manufacturing requirement, not a recommendation

Inside the main grooves of your tire there are small raised bridges of rubber. When the tread wears down until those bridges sit flush with the surrounding tread, the tire has reached a specific depth. That depth is set by federal standard.

FMVSS No. 139, which governs new radial tires for vehicles of 10,000 pounds GVWR or less — that is, the tires on almost every car in the country — says at S5.4:

“Except in the case of tires with a 12-inch or smaller rim diameter, each tire shall have not less than six treadwear indicators spaced approximately equally around the circumference of the tire that enable a person inspecting the tire to determine visually whether the tire has worn to a tread depth of one sixteenth of an inch.”

The older FMVSS No. 109 puts it in millimetres: the tire “shall incorporate a tread wear indicator that will provide a visual indication that the tire has worn to a tread depth of 1.6 mm (1/16 inch).”

One sixteenth of an inch is two thirty-seconds. Michelin’s own replacement guidance says the same thing from the other direction: “When the tread surface wears down to the same level as these indicators, 2/32 inch (1.6 mm), the tire has reached its minimum tread depth and should be replaced.”

Now put that next to California. In California, a tire whose wear bars are already flush with the tread is still legal, and stays legal for another 1/32 of an inch. One thirty-second of an inch is 31.25 mils, so at a wear rate of 5 mils per 1,000 miles that is 6,250 more miles driven on a tire that the manufacturer, the federal manufacturing standard and every tire maker in the search results all consider finished.

That is the single most useful thing on this page, and none of the twenty readable results contains the string “1/32”.

How to check tread depth, and where the regulations say to measure

The measurement is the easy part. Where you measure is what people get wrong, and the regulations are specific about it.

The gauge. A tread depth gauge calibrated in thirty-seconds costs a few dollars and is the only method that gives you a number rather than a verdict. Virginia’s statute assumes one: it specifies a reading “by a tread depth gauge calibrated in thirty-seconds of an inch.”

The penny. Insert a penny into a groove with Lincoln’s head pointing down and toward you. If the top of his head is visible, the tread is below roughly 2/32 and the tire is at the wear bars. This is the test the tire industry teaches and it is a pass/fail, not a measurement.

The quarter. Same idea with Washington’s head, which sits deeper — roughly 4/32. Bridgestone’s page, one of the two manufacturer results, recommends this one for wet-weather driving: reaching Washington’s head means “you have at least 4/32″, which is recommended for safe driving in wet weather.”

The wear bars. Free, always present, and by S5.4 there are at least six of them around the tire. Flush with the tread means 2/32.

Where to put the gauge, per the rules themselves:

• In two adjacent major grooves, not one. California, Washington and Virginia all say so. A single groove can be the one groove that is fine.
• At three locations spaced approximately equally around the tire. Washington and Virginia both require this, and 49 CFR 570.9(a)(1) describes the same procedure. A tire can be legal at the valve stem and bald a third of the way round.
• Not on the tie bars. Every one of these texts carries the same exclusion — California § 27465(c): “The measurement of tread depth shall not be made where tie bars, humps, or fillets are located.” Tie bars are the raised connectors between tread blocks. Measure on them and you will read a depth the tire does not have.
• Across the width, not just in the middle. Inner shoulder, centre, outer shoulder. If those three disagree, you do not have a tread depth problem, you have the problem described further down.

The arithmetic that turns tread depth into your own number

Here is the calculation nobody in those thirty-four results performs, and it is the one that answers the question in the headline. It uses the federal government’s own unit.

A tire has a fixed budget of usable rubber. It is the difference between the depth it left the mould with and the depth at which it is finished:

Usable tread = new depth − minimum depth

A common new all-season passenger tire is around 10/32 to 11/32 of an inch deep; performance tires are shallower, light-truck and winter tires deeper. Read the spec for your own tire, or measure a new one, rather than taking the example below as a fact about your car.

Take 10/32 new and 2/32 as the end point. That is 8/32 of an inch, which is a quarter of an inch, which is 250 mils — the mil being the thousandth of an inch, and mils per 1,000 miles being exactly the unit 49 CFR 575.104 uses to express tire wear.

Life in miles = usable mils ÷ wear rate in mils per 1,000 miles × 1,000

You get your own wear rate the same way the government gets its: measure the tread, drive, measure again, divide. Two measurements six months apart is enough. Here is what the answer looks like, with the years column computed at the FHWA average of 11,026 miles per year.

Wear rate (mils per 1,000 mi)	Life from 250 mils of tread	Years at 11,026 mi/yr
3.5	71,400 mi	6.5
4.0	62,500 mi	5.7
5.0	50,000 mi	4.5
6.25	40,000 mi	3.6
7.0	35,700 mi	3.2

And read that table the other way round, because it contains the real answer to “how long do tires last”:

Tread life in miles	Years at the U.S. average
30,000	2.7
40,000	3.6
50,000	4.5
60,000	5.4
70,000	6.4
80,000	7.3

The crossover matters. A tire sold with a 60,000-mile tread life reaches it after five years and five months of average American driving. A tire that genuinely delivers 70,000 miles takes six years and four months — by which point the age question below has already arrived. For the average driver, a long-life tire does not last longer in years. It just changes which of the two limits gets there first.

If you drive appreciably less than 11,026 miles a year — and a great many people do — then the calendar, not the tread, is what will retire your tires. That is a different decision, and it is the next section.

Age: the four digits almost nobody has looked at

A tire has a birthday and it is stamped on it. 49 CFR 574.5(b)(3):

“The date code, consisting of four numerical symbols, is the final group. The date code must identify the week and year of manufacture. The first and second symbols of the date code must identify the week of the year by using ’01’ for the first full calendar week in each year… The third and fourth symbols of the date code must identify the last two digits of the year of manufacture.”

The regulation even works an example: “0109 means the tire was manufactured in the first full calendar week of 2009, or the week beginning on Sunday, January 4, 2009, and ending on Saturday, January 10, 2009.”

So 3223 is the 32nd week of 2023. The four digits are the last group of the Tire Identification Number, the string that begins with the letters DOT.

Two things about it are worth knowing, and only one of them is on the tire-industry pages.

First: it is required on one sidewall only. Section 574.5(a)(1) obliges the manufacturer to “conspicuously label on one sidewall of each tire it manufactures”. There is no requirement that it be the outward-facing one. Roughly half the time, on a given wheel, the date code is pointing at the suspension and you will not see it without getting under the car or turning the wheel to full lock. If you have checked your tires’ age and found nothing, this is almost certainly why.

Second: no federal rule retires a tire by age. Not 570.9, which is 236 words about depth, matching, condition and damage, with no mention of age. Not 393.75. Not Part 571. The only age information federal law requires is those four digits — and then it says nothing about what to do with them.

The guidance that exists comes from the manufacturers, and Michelin states it plainly on the page that ranks for this search:

“After five years of service, tires should be thoroughly inspected at least once a year by a trained tire professional.”

“As a precaution, Michelin recommends replacing tires ten years after their date of manufacture, regardless of remaining tread depth or apparent condition. This recommendation includes spare tires.”

Five for inspection, ten as a hard stop, and explicitly including the spare — which is the tire most likely to be a decade old, because it has never been looked at. Many vehicle manufacturers publish a six-year figure in the owner’s handbook instead. Both are recommendations, not law; check the handbook for your own car before assuming either.

There is a small irony here that is worth naming fairly. Michelin’s own guidance says to stop “relying on mileage alone” — and Michelin’s own sidewalls, like everyone else’s, carry a treadwear number that reads exactly like a mileage. Both things are true at once, and the sidewall is the one people read.

Uneven wear: what the pattern is telling you

If the three measurements across the width of a tire disagree, the tire is not wearing out. Something is wearing it out. The pattern names the cause, and two of the four are pure geometry.

What you see	What it usually means	What to do
Worn strip down the centre, shoulders fine	Over-inflation: the tread crowns and rides on its middle	Set to the door-jamb placard pressure, cold
Worn both shoulders, centre fine	Under-inflation: the tread bows and rides on its edges	Same, and find out why it lost the air
Worn one shoulder only	Camber or toe out of specification	Alignment measurement — pressure will not fix it
Feathered edges, sharp one way and rounded the other	Toe error, felt as a sawtooth when you run a hand across the tread	Alignment
Cupping or scalloping, dips at intervals around the tire	The wheel is bouncing: worn dampers, or a serious imbalance	Suspension inspection; Monroe, a damper manufacturer on this search, describes the same mapping
Flat spots in one or two places	Locked-wheel braking, or long storage on one spot	Inspect; a flat-spotted tire is often finished

The first two rows are not a matter of opinion. An over-inflated tire is a rounder tire, so its contact patch narrows onto the centre rib. An under-inflated tire flattens, its centre lifts, and the shoulders carry the load. You can predict both from the shape of the thing.

Your tire pressure warning light is not an early warning

This is the part that connects inflation to wear, and it is written into the standard that created the warning light.

FMVSS No. 138, at S4.2(a), requires the system to:

“Illuminate a low tire pressure warning telltale not more than 20 minutes after the inflation pressure in one or more of the vehicle’s tires, up to a total of four tires, is equal to or less than either the pressure 25 percent below the vehicle manufacturer’s recommended cold inflation pressure, or the pressure specified in the 3rd column of Table 1 of this standard…, whichever is higher.”

Twenty-five percent below placard. On a car whose door jamb says 35 psi, the light is not required to come on until the tire is at 26.25 psi.

Placard pressure	Light not required until	Air you can lose in silence
30 psi	22.5 psi	7.5 psi
32 psi	24.0 psi	8.0 psi
35 psi	26.25 psi	8.75 psi
36 psi	27.0 psi	9.0 psi

Every psi in that gap is a tire running flatter than it should, wearing its shoulders, running hotter and costing fuel — with the dashboard perfectly dark. The system was designed after a series of underinflation-related tread separations; it is a blowout warning, and it is a good one. It is not a maintenance tool. A five-dollar gauge once a month is, and it is the single cheapest thing on this page.

If fuel economy is what you care about, this is where a measurable part of it goes, and it interacts with everything else in the cars with the best gas mileage comparison — where the EPA’s own figures assume a properly inflated tire.

How often to rotate: what the government does when it is measuring

The standard advice is every 5,000 to 7,500 miles, or at every oil change. That advice is fine. What is missing is why it exists, and the regulation answers that better than any of the search results do.

When NHTSA measures how fast a tire wears, section 575.104(e)(2)(viii)(A) instructs:

“After every circuit (approximately 400 miles), rotate each vehicle’s tires by moving each front tire to the same side of the rear axle and each rear tire to the opposite side of the front axle.”

Every 400 miles. Sixteen times over the 6,400 graded miles. That is between twelve and nineteen times more often than the interval anyone recommends to a driver — and the reason is not that the agency is fussy. It is that wear is a property of the position, not of the tire. The front tires of a front-wheel-drive car steer, brake harder and carry the engine; left them in place, they would wear out while the rears still looked new, and the measurement of the tire would be contaminated by the corner. The convoy also rotates the cars themselves every 800 miles, for the same reason.

Note the pattern in that sentence, because it is the one the government uses: fronts go straight back to the same side, rears cross over to the opposite front corner. That is the rearward-cross pattern, and it is the standard one for rear-wheel and four-wheel drive. Front-wheel-drive cars usually use the mirror image, forward cross. Directional tires, and staggered fitments where front and rear are different sizes, restrict what is possible — check the handbook.

The practical translation is simple. Rotation does not make tires last longer in total rubber. It makes all four arrive at the end together, which means you replace four at once instead of two and two, and it means the wear pattern you read in the table above reflects the car rather than one corner of it. When rotation belongs in the rest of the service calendar is laid out in car maintenance schedule, along with the question of who actually decides those intervals.

Two tires or four, and which axle

If only two tires need replacing, the answer is not the intuitive one.

Michelin’s guidance on the page that ranks for this search: “The ideal is always four matching tires. If only one is damaged or worn, the replacement should match the other three as closely as possible in brand, model, size, and remaining tread depth. If replacing two, fit both on the rear axle.“

New tires go on the back even on a front-wheel-drive car. The reasoning is about what happens when grip runs out in the wet: if the front loses grip first the car pushes wide, which is alarming and correctable with the steering; if the rear loses grip first the car rotates, which is neither. Deeper tread on the rear axle keeps the failure in the direction a driver can handle.

The all-wheel-drive case is stricter. Michelin: “Replacing a single tire on an AWD or 4WD vehicle requires extra care, as significant differences in circumference across the four tires can stress the drivetrain.” A worn tire is a smaller tire, it turns faster for the same road speed, and a permanently-coupled differential reads that as slip. Some manufacturers publish a maximum tread-depth difference across the axles; that number is in the handbook and it is worth finding before buying one tire.

What a tire actually costs you per mile

The honest answer to “how long do tires last” ends in money, because that is what the question is usually about.

Tires are one of the few running costs that are genuinely and cleanly proportional to distance. Fuel is too. Depreciation is partly. Insurance and registration are not proportional to anything you do. So tires belong in the per-mile column, and the arithmetic is one division:

Cost per mile = price of the set, fitted ÷ miles the set delivers

Set price, fitted	40,000 mi	50,000 mi	60,000 mi
$600	1.50 ¢/mi	1.20 ¢/mi	1.00 ¢/mi
$800	2.00 ¢/mi	1.60 ¢/mi	1.33 ¢/mi
$1,000	2.50 ¢/mi	2.00 ¢/mi	1.67 ¢/mi
$1,200	3.00 ¢/mi	2.40 ¢/mi	2.00 ¢/mi

Somewhere between one and three cents a mile, for most cars. Set that beside the IRS standard mileage rate, which is 72.5 cents for 2026 — the full mechanics of that number are in IRS mileage rates 2026 — and tires are on the order of one and a half to four percent of what a mile of driving officially costs. It is not the biggest line. It is, however, the one where a purchase decision and a maintenance habit both show up directly in the number, which is not true of most of the others. The method for assembling the whole figure for your own car is in car cost per mile.

There is a second, larger sum hiding in the same table: buying a $1,000 set that delivers 60,000 miles beats a $600 set that delivers 30,000 by a third of a cent a mile, and buying the cheap set twice costs more in fitting alone. The treadwear grade is the only comparative signal you get about which is which before you buy — which is why it is worth understanding what it is, and worth not mistaking for a guarantee.

The one check to do when you buy a used car

Before leaving this: a set of four matching tires with the same date code and even wear tells you something real about how a used car was kept, and a set of four mismatched tires tells you something else. It costs thirty seconds and it is one of the few claims about a used car that cannot be talked away, because the evidence is molded into the rubber.

Check the date codes on all four — remembering that the code may be on the inboard sidewall — and run the penny test at three points on each. Four tires from four different weeks, or one new tire among three worn ones, is not necessarily a problem, but it is a question with an answer that you are entitled to hear. That check sits alongside the others in questions to ask when buying a used car, and the reasoning for why the odometer beats the model badge is in best cars for resale value.

The one independent measurement in the search results

It is only fair to name the exception. Of the thirty-four organic results, exactly two are independent testing, and one of them publishes its method.

Consumer Reports runs its own treadwear programme, and the scale is worth putting next to the federal one. Its page for this search reports “More than 350,000 vehicle miles were logged this year to generate” its treadwear ratings, and gives 2023 as the worked example: “eight almost identical Toyota Camrys were used in” the treadwear test “over a six-month period”, covering “64 tires for a total of 1,024,000 tire miles that year”.

Divide it out: 16,000 miles on each tire, against the 6,400 graded miles of the federal protocol. An independent magazine drives each tire two and a half times as far as the regulation that grades it does. That is not a criticism of NHTSA, whose test is designed to be reproducible and cheap enough that every manufacturer can run it. It is a reason to treat the sidewall number as a coarse sort, and an independent test as the finer one.

What I would actually do with all of this

Four things, in order of how much they are worth.

1. Buy a tread depth gauge. A few dollars, and it converts every one of the arguments above from a verdict into a number. Measure all four tires, in two adjacent grooves, at three points around each, at the inner shoulder, centre and outer shoulder. Write down the readings and the odometer alongside them.
2. Do it again in six months. The difference, divided by the miles driven, is your wear rate in mils per 1,000 miles — the same unit the federal government uses. Put it in the table above and you have a replacement point that is about your car, not about a course in Texas.
3. Read the date codes now, including the spare, and remember that the code may be on the sidewall facing the car. Five years is when the inspections start mattering; ten is where the manufacturer says stop.
4. Check pressures monthly with a gauge, not with the dashboard. The warning light is legally allowed to stay dark until you are 25 percent down, and the shoulder wear starts long before that.

None of this needs an app. What it needs is a place where the twelve numbers and the odometer reading from step 1 are still there in six months, which is where most people lose the thread — the measurement gets taken, and then it lives on a scrap of paper in the glovebox until the next tire is already bald.

I built Magica for exactly that gap. It records trips automatically, so the odometer figure that step 2 divides by is already there without anyone remembering to write it down. It keeps a maintenance log with photos and receipts attached, so “measured 8/32 across all four on 23 August” is a record and not a memory, and so is the fitting invoice with the date codes on it. And it will remind you on a date or at a mileage, which is the form the tire question actually takes: not “is it worn out” but “when do I look again”.

All of it stays on the device — there is no account and no server of mine holding a history of where a car has been. If you would rather keep the log on paper, the structure of what to record is the same, and it is set out in car maintenance log.

FAQ

How long do tires last?

Between roughly three and seven years, and the range is that wide because two different limits are racing each other. On tread, a tire has about 250 mils of usable rubber between a typical 10/32 inch new depth and the 2/32 inch minimum, which at the U.S. average of 11,026 miles a year works out at about 4.5 years for a 50,000-mile tire and 5.4 years for a 60,000-mile one. On age, Michelin recommends yearly professional inspection after five years and replacement at ten “regardless of remaining tread depth”, and many carmakers publish six years in the handbook. Whichever limit arrives first is your answer.

How many miles do tires last?

Commonly 30,000 to 70,000, depending on the tire and on how it is driven, but you can compute your own instead of guessing. Measure the tread depth, drive, measure again, and divide the loss by the miles: that gives a wear rate in mils per 1,000 miles, the unit 49 CFR 575.104 uses. Divide your usable tread — new depth minus 2/32 of an inch, in mils — by that rate, multiply by 1,000, and the answer is in miles.

What is the minimum legal tire tread depth?

It depends on the state, which is the part most guides skip. The federal criterion for state inspection programmes is 2/32 of an inch (49 CFR 570.9), but Part 570 states at section 570.3 that it “does not in itself impose requirements on any person”. Virginia (§ 46.2-1043) and Washington (RCW 46.37.425) set 2/32. California sets 1/32 for ordinary passenger cars (Veh. Code § 27465(b)(1)), 4/32 on the steering axle of commercial vehicles, and 6/32 for snow tires used instead of chains. Federal rules for trucks and buses (49 CFR 393.75) require 4/32 on the front wheels.

When should I replace my tires, as opposed to when am I allowed to?

Earlier than the legal floor. The wear bars are molded to one sixteenth of an inch — 2/32 — by FMVSS No. 139 S5.4, and every tire maker treats that as the end of service life. Bridgestone recommends replacing at 4/32 for wet-weather driving, which is the depth of Washington’s head on a quarter. If you drive in rain or snow, treat 4/32 as the decision point and 2/32 as the deadline.

What does the treadwear number on my tire mean?

It is a comparative grade, not a mileage. Under 49 CFR 575.104 a tire is driven in a convoy over a 400-mile course near San Angelo, Texas, for 16 circuits — about 6,400 graded miles after an 800-mile break-in — its wear rate is measured in mils per 1,000 miles, corrected against reference tires run alongside it, expressed as a percentage of those reference tires and then rounded down to the nearest 20 points. A grade of 400 means twice the wear resistance of a grade of 200 on that course. It is not a promise of 400 anything.

How do I read the date code on a tire?

Find the letters DOT on the sidewall and read the last four digits of the string that follows. Under 49 CFR 574.5(b)(3) the first two are the week and the last two are the year: 3223 is the 32nd week of 2023. The regulation’s own example is “0109 means the tire was manufactured in the first full calendar week of 2009”. The code is only required on one sidewall, and it is not always the outward-facing one, so check the inboard side before concluding the tire has no date.

How often should I rotate my tires?

Every 5,000 to 7,500 miles is the usual recommendation, and aligning it with oil changes is the easiest way to remember. The reason is that wear depends on the corner of the car more than on the tire: when NHTSA measures tire wear for grading purposes it rotates the tires every 400 miles, sixteen times in 6,400 miles, precisely to cancel that effect out. The pattern the regulation uses is fronts straight back to the same side, rears crossed to the opposite front — check the handbook for directional or staggered fitments.

Why are my tires wearing unevenly?

Wear down the middle means over-inflation; wear on both shoulders means under-inflation; wear on one shoulder only, or a feathered sawtooth edge, means the alignment is out and no amount of air will fix it; regular dips around the circumference mean the wheel is bouncing, usually worn dampers. Check the pressures cold against the door-jamb placard first, since that is free and it rules out two of the four.

Do new tires go on the front or the back?

The back, even on a front-wheel-drive car, when only two are being replaced. Michelin’s guidance is explicit: “If replacing two, fit both on the rear axle.” Deeper tread on the rear keeps the car pushing wide rather than spinning when grip runs out in the wet. On all-wheel drive, check the handbook before replacing fewer than four: differences in rolling circumference between worn and new tires load the drivetrain.

Does the tire pressure warning light mean my tires are fine?

No. FMVSS No. 138 S4.2(a) requires the light to come on when a tire is 25 percent or more below the manufacturer’s recommended cold pressure. On a 35 psi placard that is 26.25 psi. Everything between those two figures is under-inflation running with the dashboard dark — enough to wear the shoulders and cost fuel, not enough to trigger the warning. Use a gauge monthly.

What this page is, and what it is not

Everything cited above is a primary source: 49 CFR 570.1 to 570.9, 571.109, 571.138, 571.139, 574.5, 575.104 and 393.75, read from the eCFR on 23 August 2026; California Vehicle Code § 27465, Washington RCW 46.37.425 and Virginia Code § 46.2-1043, read from the states’ own legislature sites the same day; and Federal Highway Administration Table VM-1 for 2023. The two quoted commercial pages, Michelin’s and Bridgestone’s, are named where they are used, as is Consumer Reports.

What it is not is a substitute for looking at your own car. State law changes, three states out of fifty is a sample and not a survey, and the tread depths a tire leaves the factory with vary by model. Read the handbook, read the sidewall, and put a gauge in the glovebox.