Tires age whether you drive on them or not. A tire that's been on a car for one year and 1,000 miles can be just as compromised as one with 50,000 miles — if it's old enough. Here's the science of tire aging and the limits you should actually respect.
What causes tire aging
- Oxidation — oxygen breaks down rubber polymers from the inside
- UV light — sunlight breaks down the outer layer
- Heat cycling — every drive heats and cools the rubber, fatiguing it
- Ozone — pavement and atmosphere produce ozone that attacks rubber
- Static load — sitting on flat tires deforms the casing over months
The 6-year recommendation
Most major tire manufacturers recommend replacing tires six years from the DOT date code regardless of tread depth or apparent condition. Michelin, Bridgestone, Continental, and Goodyear all publish this. The reasoning: after six years, tire reliability becomes statistically unpredictable. A specific tire may be fine, but the overall failure rate climbs.
The 10-year hard limit
Tires older than ten years from manufacture should not be on a vehicle in service. Period. Most manufacturers refuse to honor warranties past ten years. Many countries' inspection regimes flag tires past ten years as a fail.
What about spare tires?
Spare tires age just like road tires, even though they almost never see road use. A spare older than six years should be inspected carefully before service, and a ten-year-old spare should be replaced even if it's never been on the ground. The rare time you need a spare is the worst time to find out it's degraded.
Used tire age — what to ask for
When buying any used tire, the DOT date code matters more than the tread depth in some ways. A reputable seller will tell you the date code of every tire they sell. We don't ship anything older than six years from today's date.
Faster aging conditions
Tires that have been stored or used in hot climates (Arizona, Nevada, the Southwest desert) age faster than tires from cool, mild climates. Tires that have been parked outdoors year-round age faster than ones that lived in garages. There's no way to precisely measure this from the outside — but if you know a tire spent its life in extreme heat, treat the six-year limit more strictly.
Signs of advanced aging
- Visible cracking, even if small
- A grayish or whitish surface bloom
- Hardness when you press your thumbnail into the rubber
- Loss of the bumpy/grippy texture
Tread tells you what you've used. The DOT code tells you what you have left.