I have some mini spares that have been treated annually with rubber preservative and kept in the garage in sealed plastic bags since they were new. How old can they get in this condition before they become unsafe to use?
Protection from light does help some, but mostly in terms of premature aging. Standards are on the way for the maximum age at which a tire can be sold. In Europe I thought they were talking about seven years. You can easily check this. So I'd say seven years and you are on your own, maybe ten at the outside. When and if a person ever must resort to a mini they should drive extra carefully and expect handling problems. It should be strictly for emergencies. It's no coincidence that I see mini spares for free or $1 at garage sales regularly.
IMO, 10 years absolute max. If they were mine, and I really wanted to keep them, I would double bag and then replace the air in the tires and in the bags with argon.
Rather than relying on guesses my recommendation would be to call the manufacturer of the tire. And then rely on their recommendation. Are you looking to resell them possibly? If so the resale market isn't particularly good.
If you keep them properly inflated and keep your speeds under the limit of the spare, they work ok. Most people don't check the tire pressure on these, so when they need to use them, they are usually dangerous because they are underinflated.
I had to use mine on a 15 year old Protege when I picked up a nail. It was stored in the spare well in the trunk, no preservative or Rosary beads in all that time and it was indifferently inflated. I inflated it to spec, mounted it on the car then drove 20 miles to work and back with no problems. This car lives in Dallas and Houston so it sees a lot of heat in the trunk.
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