Guides · Field note
Why tire age still matters when the tread looks fine
A tire can have plenty of tread and still be the wrong tire to put back on the car. Rubber ages whether it is driven or sitting in a trunk. Michelin and Continental publish a ten-year maximum from the date of manufacture, including the spare. Ford tells owners to replace tires at six years regardless of tread. NHTSA does not set a federal retirement age. Transport Canada does not set one either. The date on the sidewall is still the number those documents tell you to read.
How to read the DOT week and year
Every highway tire sold in the United States and Canada carries a Tire Identification Number that begins with DOT. The last four digits are the date of manufacture. NHTSA’s 49 CFR 574.5 and Canada’s Motor Vehicle Tire Safety Regulations use the same code: the first two digits are the week (01 through 53), the last two are the year. A sidewall ending in 2714 was built in the 27th week of 2014. Michelin’s example is 3520 — the 35th week of 2020.
NHTSA’s consumer TireWise page repeats the same reading: if the TIN ends in 0308, the tire was made in the third week of 2008. Look at both sidewalls. The full date is not always moulded on the outward face. Tires built before 2000 used a three-digit date. Continental still publishes that older format so a 1990s spare is not misread as a recent tire.
Transport Canada’s Riding on Air pamphlet (TP 2823) points to the same four-digit fabrication code on the sidewall. The maple-leaf national safety mark next to it certifies the tire met Transport Canada’s construction standard when it was new. It is not an expiry date.
What the manufacturers and vehicle makers publish
Michelin
Michelin’s U.S. and Canadian replacement pages use the same two thresholds. After five years of service, have the tires inspected at least once a year by a professional, even if they look fine and have not reached the treadwear indicators. As a precaution, replace them ten years after the date of manufacture, “regardless of remaining tread depth or apparent condition.” The ten-year line includes spare tires. For original-equipment tires, Michelin tells owners to follow the vehicle maker when that advice is tighter.
Continental
Continental is not aware of technical data that would force every tire out of service at one specific age. It still advises, with the rest of the tire and automotive industries, that all tires — including spares — more than ten years old should be removed from service and replaced, even when the outside looks usable and the tread is above the legal limit. Drivers “cannot depend on visual inspection for rubber cracking, wear to the tread, or other signs of deterioration from age.” If the vehicle maker publishes a younger age, Continental says to follow that.
Ford
Vehicle makers are often stricter than tire makers. Ford’s consumer tire-care page:
In general, Ford Motor Company recommends tires should be replaced after six years regardless of tread wear. You should replace your spare tire when you replace the road tires or after six years due to aging even if it has not been used.
Ford’s replacement page repeats the six-year mark for the spare “even if it has not been used.” That is a vehicle-maker limit, not a federal one. The owner’s manual for the vehicle in front of you is the document that governs that car.
There is no legal maximum age in the United States or Canada
NHTSA studied tire aging and did not write a retirement age into FMVSS. Its TireWise aging page says you cannot detect aging simply by looking, then points owners to manufacturer guidance: “Some vehicle and tire manufacturers recommend replacing tires that are six to 10 years old, regardless of treadwear.” That is a summary of those published recommendations, not a regulation.
Canada’s Motor Vehicle Tire Safety Regulations require the week-and-year date on the sidewall. They do not require a tire to be removed at six years, ten years, or any other calendar age. Transport Canada’s consumer pamphlet tells owners to replace tires for wear, cuts, cracks, blisters, or bulges. It does not publish a maximum service life. A CSA age limit for passenger tires is not a document we can point to. If a province or state later writes one into an inspection rule, that rule — not this page — is the one that applies there.
Ozone, dry rot, and why appearance is not the test
USTMA’s Care and Service of Passenger and Light Truck Tires describes weather checking, also called ozone cracking: direct and extended exposure to ozone and heat from sunlight, or to ozone from electric motors, welders, and similar sources. Tires with severe weather checking, or any crack that reaches the casing cords, are out of service. Excessive cracking on the tread or sidewall is also removal; USTMA lists underinflation, overload, improper storage, and long-term parking as typical causes.
Michelin’s replacement FAQ adds heat cycles, ultraviolet light, and ozone as ways rubber degrades that “aren’t visible on the surface.” That is the same point Continental makes: a tire can look functional and still be past the age those makers treat as a maximum. Dry rot is the shop word for that cracking. The published name is ozone or weather checking. Either way, remaining tread does not reverse it.
NHTSA’s aging page says the people most likely to meet an old tire with unused tread are low-mileage drivers, collector cars, recreational vehicles, and anyone who leaves a spare in place for the life of the vehicle. Heat and sunlight make the same chemistry faster. The agency still does not turn that into a legal age.
Why a 12-year spare can be unsafe
A compact spare that has never been on the road still ages from the DOT date. Michelin says so in those words. Ford’s six-year spare rule is written for a tire that “has not been used.” NHTSA: spare tires “are prone to aging because they seldom get replaced,” and a full-size spare should not be treated as a long-term stand-in for worn road tires except in an emergency.
A spare stamped in 2014 is twelve years old in 2026. That is past Ford’s six-year vehicle-maker line and past Michelin’s and Continental’s ten-year maximum. The tread can still look new. The rubber has still been sitting through a decade of heat, ozone, and underinflation in a well or on a carrier. Putting that tire on a highway at speed is the use those documents are written to prevent.
What this means on a driveway
When the tread looks fine and the customer wants to keep the set, read the DOT date. If the vehicle maker publishes six years, that is the number for that car. If the tire maker publishes ten, that is the outer limit those companies will stand behind, including the spare. Neither country has made either figure a statute. The honest sentence is still: age is a replacement reason even when the wear bars are not showing.
That recommendation is in the manufacturer pages linked below. It is not a registry rule, and it is not a verification of any operator. Check the manual for the specific vehicle and the sidewall for the date.
Sources
- Michelin USA, “When to Replace Tires.” Five-year inspection; ten-year maximum from manufacture, including the spare; DOT example 3520. https://www.michelinman.com/auto/auto-tips-and-advice/tire-buying-guide/when-do-i-need-new-tires
- Michelin Canada, “When to Replace Tires.” Same five-year and ten-year guidance, including spares. https://www.michelin.ca/en/auto/learn/tire-buying-guide/when-to-replace-tires
- Continental Tires, “Replacing tires.” All tires including spares more than ten years old should be replaced; how to read the four-digit DOT date. https://www.continental-tires.com/tire-knowledge/replacing-tires/
- Ford Motor Company, “How to Care for Your Tires.” Replace after six years regardless of tread; spare after six years even if unused. https://www.ford.com/support/how-tos/tires-and-wheels/tire-replacement-and-maintenance/how-to-care-for-your-tires/
- Ford Motor Company, “Tire Replacement.” Spare after six years even if it has not been used. https://www.ford.com/support/how-tos/tires-and-wheels/tire-replacement-and-maintenance/tire-replacement/
- National Highway Traffic Safety Administration, TireWise, “Aging.” No look-only test; some makers recommend six to ten years; how to read the TIN; spare-tire caution. https://www.nhtsa.gov/equipment/tires
- NHTSA, 49 CFR 574.5, tire identification: four-digit week and year date code. https://www.law.cornell.edu/cfr/text/49/574.5
- Transport Canada, Motor Vehicle Tire Safety Regulations, SOR/2013-198, section 6: four-digit week and year of manufacture. No calendar retirement age. https://laws-lois.justice.gc.ca/eng/regulations/SOR-2013-198/section-6.html
- Transport Canada, Riding on Air, TP 2823. Four-digit fabrication code; replace for wear or visible damage, not a published age limit. https://tc.canada.ca/en/road-transportation/stay-safe-when-driving/riding-air
- U.S. Tire Manufacturers Association, Care and Service of Passenger and Light Truck Tires. Ozone cracking / weather checking; remove tires with severe cracking or cracks to the cords. https://www.ustires.org/system/files/files/2024-08/Care%20and%20Service%20of%20Passenger%20and%20Light%20Truck%20Tires%202017_0.pdf
Questions that come up
Is there a legal maximum tire age in the United States or Canada?
No. NHTSA has not written a retirement age into federal safety standards. Transport Canada requires the week-and-year date on the sidewall and does not require removal at a set age. The six-year and ten-year figures are manufacturer and vehicle-maker recommendations.
How do I read the date on the sidewall?
Find the DOT Tire Identification Number. The last four digits are week and year. 2714 is the 27th week of 2014. NHTSA, Michelin, Continental, and Transport Canada all publish that reading. Check both sidewalls; the full date is not always on the outward face.
Why would a spare that has never been driven be unsafe?
Rubber ages in storage. Michelin’s ten-year maximum and Ford’s six-year spare rule both apply to tires that have not been used. NHTSA notes that spares are the tires most likely to sit past those ages because they are seldom replaced.
The tread looks fine and there are no cracks. Does age still matter?
Yes, according to the makers who published a maximum. Continental says you cannot depend on a visual inspection for age. Michelin says materials degrade even with light use. USTMA still wants visible ozone cracking treated as a removal condition when it is severe or reaches the cords.