Your tread is legal and your tires are still finished

In most of the country a tire wears out before it gets old. In Los Angeles it is often the other way round, and the state's own rules already say so.

California's passenger-car tread minimum is one thirty-second of an inch — half the familiar 2/32 figure, and the subject of the California tread law page. A city where the legal floor is that low, the roads never freeze and a lot of cars barely move needs a second measurement. That measurement is four digits on the sidewall.

California regulation names age, in a definition that binds a fitter

Title 17 of the California Code of Regulations, section 95550, is the ARB's "Regulation for Under Inflated Vehicle Tires". Filed 30 August 2010, operative 1 September 2010. Its definitions section includes this one:

"Unsafe Tire" means any tire considered unsafe in accordance with standard industry practices, due to tire tread wear, age, tread irregularity, or damage. Examples include any tire with exposed ply or cord, sidewall crack, bulge, knot, or ply separation.

Read the list of causes: tread wear, age, tread irregularity, damage. Age is named alongside wear, in a state regulation, as a ground for calling a tire unsafe. And the definition does work, because 95550(d)(3)(B) relieves a service provider of its duty to inflate a tire it has determined to be unsafe.

That is why "your tread is fine and your tires are too old" is not a sales line in this state. It tracks the wording of a regulation that binds the person holding the gauge.

The same section is where California's check-and-inflate duty lives, and it is unusually specific. Automotive service providers are required to:

(A) check and inflate each vehicle's tires to the recommended tire pressure rating, with air or nitrogen, as appropriate, at the time of performing any automotive maintenance or repair service; and (B) indicate on the vehicle service invoice that a tire inflation service was completed and the tire pressure measurements after the services were performed; and (C) perform the tire pressure service using a tire pressure gauge with a total permissible error no greater than + two (2) pounds per square inch (psi); and (D) have access to a Tire Inflation Reference that is current within three years of publication; and (E) keep a copy of the vehicle service invoice for a minimum of three years...

An "Automotive Service Provider" is defined broadly enough to cover us — "any business ... that performs or offers to perform automotive maintenance or repair services (including, but not limited to, automotive dealerships, maintenance or repair garages ... oil change facilities, tire centers, and smog check facilities)". The "Recommended Tire Pressure Rating" is the manufacturer's specification "found on the vehicle's door placard, glove box door, or owner's manual" — not the number moulded into the tire. What the tire pressure placard means explains the difference. An "Under Inflated Tire" is one "that is one pound per square inch (psi) or more below the recommended tire pressure rating".

California requires this. We have not surveyed the other forty-nine states, so we are not going to tell you it is the only one that does.

The four digits

The date code is federal, which is why no state repeal can touch it. 49 CFR 574.5(b)(3), read at eCFR:

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, "02" for the second full calendar week, and so on ... For 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.

The date code is the last group of the Tire Identification Number, which on a new tire is thirteen symbols: a three-symbol plant code, a six-symbol manufacturer's code and the four-symbol date code. The old two-symbol plant code could be used only until 13 April 2025, so tires reaching a Los Angeles kerb from here on carry the three-symbol version. The TIN is moulded into one sidewall, so check the other side of the wheel before you decide it is missing.

So a tire reading 2419 was built in the twenty-fourth week of 2019. That is when it was made, not when it was fitted, and the gap can be long, because a tire ages on a rack as well as on a car.

How old the cars around you actually are

The California DMV publishes a registered-vehicle count by ZIP, model year and fuel. The release dated 1 January 2026, snapshotting 31 December 2025, records 29,658,134 registered light-duty vehicles in California. Of those, 21,384,861 are model year 2020 or older — 72.1 percent (DERIVED: 21,384,861 divided by 29,658,134). 13,682,322, or 46.1 percent, are model year 2015 or older. 8,834,475, or 29.8 percent, sit in the DMV's oldest bucket, which it publishes as "<2012" and cannot be split further.

Model year 2020 is six model years ago as of 2026. A tire fitted at the factory on a model-year-2015 car and never changed is now eleven years old.

Some Los Angeles ZIPs run older than the state. 80.9 percent of the light-duty vehicles registered in 90044, in South Los Angeles, are model year 2020 or older; 90002, Watts, is at 80.6 percent. At the other end of the seventeen Los Angeles ZIPs we can use, 91403 in Sherman Oaks is at 57.0 percent and 91367 in Woodland Hills at 57.5. That is a 23.9-point spread inside one city, ranked over those seventeen ZIPs and nothing wider. Neighbourhood pages: South Los Angeles, Wilmington, Highland Park, Sherman Oaks.

One ZIP is excluded from all of this on purpose. 90045 — Westchester, Playa del Rey and LAX — records 101,503 registered light-duty vehicles against 41,786 residents, with 39,968 of model year 2025. Those are airport rental fleets, and no fleet-age statistic computed from them means anything.

And how little some of them are driven

The American Community Survey 2020-2024 five-year estimates put 19.5 percent of City of Los Angeles workers at home rather than commuting. In four of the eighteen Los Angeles ZIP areas in our research the share is above 30 percent: 90291 Venice at 44.7 percent, 91403 Sherman Oaks at 37.6, 90025 West Los Angeles at 32.4, 90066 Mar Vista at 31.2.

A car driven a few thousand miles a year does not wear its tread out. It ages out with the tread still on it. Those households are exactly the ones a tread-depth conversation will reassure and a date code will not.

What NHTSA found, and where it found it

The agency's own summary of its tire-ageing work, "TIRE AGING: A Summary of NHTSA's Work", U.S. Department of Transportation, March 2014, is the standard reference. A sourcing note first, because it matters: nhtsa.gov returned 403 to every attempt we made on 2026-09-20, so the copy we read and are quoting is the one hosted by the trade magazine Tire Review, at the URL in our sources list. The document's title page is intact and the quotations below are verbatim from it. We have not read the agency's own copy.

On why ageing is not a maintenance failure you can tidy up:

The common belief is that tire failures are caused by poor maintenance. Proper tire maintenance is important for good wear and the safety performance of a tire, but tire aging is a degradation phenomenon that can occur due to the chemical reaction within the rubber components with oxygen and heat. This is different from inadequate inflation and maintenance problems. Some vehicle manufacturers recommend that tires be replaced every six years regardless of use and a number of tire manufacturers recommend 10 years as the maximum service life for a tire because aging can affect the performance of the tires even if they have adequate tread and proper inflation.

On where it bites, and this is the sentence that inverts the usual advice for this city:

Tires in service in the northern states are generally replaced before tire aging becomes an issue, but aging is still a concern in the Sun Belt states for light vehicle tires, in the summer months, during the day, when they are driven at highway speeds.

On insurance claims, from data covering 2002 to 2006, with California named:

It reported that 27 percent of its policy holders are from Texas, California, Louisiana, Florida, and Arizona, but 77 percent of the tire claims came from these states and 84 percent of these involved tires over six years old.

NHTSA attaches its own caveat to those numbers and it travels with them here: "While tire insurance claims are not necessarily an absolute measure of the failures due to aging, it is reasonable to assume that a considerable number of insurance claims for tire adjustments in the four states listed combined with NHTSA's fatality data and NMVCCS data given above is an indication that a large number of tire failures are likely occurring because of the effect of sustained high temperature on tires."

And on the spare, which nobody looks at:

Spare tires remain a concern as well, since they are not replaced regularly and may still show enough tread, even though the structural integrity of the tire may be compromised by aging. Adding to this concern, spare tires are often rotated into use and are sold as used tires.

That last clause is one reason we do not sell used tires and do not fit a set bought elsewhere. A part-worn tire carries somebody else's date code and somebody else's summers. Why we will not fit used tires is the argument in full. Does my car have a spare tire? is where to start on the one in the boot.

The heat that does it is not evenly spread

NHTSA's mechanism is oxygen and heat. Los Angeles has two answers to how much heat, twenty miles apart.

On the NOAA 1991-2020 annual normals, Los Angeles International averages 23.3 days a year at or above 80F, 2.5 at or above 90F and 0.0 at or above 100F, with an annual mean maximum of 69.0F. Van Nuys Airport, inside the same municipal boundary, averages 148.3 days at or above 80F, 63.2 at or above 90F and 7.8 at or above 100F, with an annual mean maximum of 77.0F. Downtown and Burbank sit between them: 112.7 and 137.7 days at or above 80F.

So the ageing argument is not one argument in this city. Valley heat against coastal heat is the page that splits it, including the fact that on the coast the hot weeks are late September and October rather than July.

We are not going to put a sunshine or UV figure next to that. NOAA's normals carry no sunshine element for any Los Angeles station, and we could not reach an irradiance source on 2026-09-20. Heat, dryness and how old the cars are is what we can actually show you.

What we do at the visit

We read the date code on all four tires and the spare, tell you what each one says, and measure the tread beside the wear bar rather than on it, because California excludes tie bars, humps and fillets from the measurement. We set the pressures to the door placard and record them, which 17 CCR 95550 requires of us anyway.

If the tires are sound we say so and leave. If the dates argue for replacement we tell you what they read and let you decide, and if you want them changed we supply and fit at the same address on the same visit. We do not fit tires bought elsewhere.

When to replace your tires covers the general case, find your tire size covers what a replacement is, how many tires to replace covers two against four, mixing tire brands covers what happens if you do not do all four, and what mobile tire replacement costs covers the money. For a damaged tire rather than an old one, mobile tire repair in Los Angeles. For where we come, our Los Angeles service area.

Our price: $145

A mobile puncture repair is $145 for the first tire and $50 for each additional tire in the same visit, with no separate call-out fee. Repair is subject to on-site inspection; if a tire cannot be repaired safely we say so, you pay for the inspection and not for a repair that was not done. Replacement is priced separately and shown on screen before you give us a phone number. For a fit we need level, paved, legal ground with room to work at one corner of the car.

Questions people ask

• Is six years a legal limit in California? No, and no federal rule sets one. NHTSA reports that some vehicle manufacturers recommend replacement every six years regardless of use and that a number of tire manufacturers give ten years as a maximum service life. What California does have is 17 CCR 95550(c)(14), which names age as one of the grounds on which a tire is considered unsafe.
• Where do I find the date code? It is the last four numerical symbols of the DOT Tire Identification Number, moulded into one sidewall only. Check both sides of the tire before concluding it is absent.
• How do I read it? First two digits are the week of the year, last two are the year. The regulation's own example: "0109 means the tire was manufactured in the first full calendar week of 2009".
• My tread is fine. Why would I replace anything? Because tread depth does not record age, and in California the legal tread floor is 1/32 of an inch, which is lower than the point at which most drivers would want to be. NHTSA's position is that ageing "can affect the performance of the tires even if they have adequate tread and proper inflation".
• Do you have to write my tire pressures on the invoice? Yes. 17 CCR 95550 requires an automotive service provider in California to check and inflate to the placard rating at the time of any maintenance or repair service, to record the measured pressures on the invoice, to use a gauge accurate to within 2 psi, and to keep that invoice for three years.
• Will the smog check catch an old tire? No. The biennial smog inspection measures emissions. Nothing in it looks at a tire, which is why the date code is the clock you have.