I’m about to replace my original tires from my 2003 k1500. The spair has never left the rack under the bed, however I’ve had it for 6 years, it could be nearly 7 years old. 4 tires is more than I want to spend 5 no way. How reliable will that spair be (fiquring I keep it inflated correctly) in a couple of years.
I wouldn’t mix your 7 year old tire with 3 new ones. As a spare I’d keep it, and get 4 new tires to run on.
Just don’t run the spare any farther than you have to.
Recent bulletins out the tire manufacturers indicate that rubber in a tire deteriorates even if the tire is unsed. There seems to be some difference in how this is stated, but it is clear that tires in hot climates deteriorate more rapidly than tires in cold climates. It seems that 6 years is the limit for hot climates and 10 years is the limit for cold climates.
Based on the fact that you have a 6 yesr old truck, it would just make sense to replace 4 tires and leave the spare where it is, replacing it when you next replace tires.
Add my opinion to the others. Keep the spare as a spare, you don’t want to mix it with three new tyres for regular driving.
I think you would be OK using a 7 year old tire as a spare. My back-up vehicle is a '76 El Camino that I bought about 8 years ago. The tires were in good condition when I bought it and at 2000 miles per year, they never wore out. I decided to run them to failure just to see how long they would last. The first one to fail was 11 years old. The failure mode was tread separation while driving. No loss of control. This vehicle was parked outside in the Texas sun for the entire time, so I regard this as a “worst case” example. I still carry a spare that is now 9 years old, but I wouldn’t drive over 45 to 50 mph with it.
I understand that rubber deteriorates over time. In motorcycles this is very important as those 2 tires are all the traction you have to rely on. In a limited ues tire, like a spare, the issue for me is really will it hold air. If the old tire stills maintain pressure over a year (check the pressure in your spare at least once a year) then I say keep it. The donut spares are meant for 50 mph max when new. So an old spare tire if needed shouldn’t be driven hard and replaced by a new tire ASAP. Then it goes back to “spare duty”.
My boat trailer had the original tires on it from 1987 until this year. The sidewalls and tread area had all kinds of cracks and evidence of old age. Yet they held air no problem. As I used the boat trailer only for storage with no over the road use I just kept them aired up once a year. This summer I took the boat and trailer on a “road trip” of about 400 miles. No way was I going to take that trip on those old tires.
I guess I’d replace a spare at 25 years or its lack of holding air pressure or whichever comes first.