This happened to me too. I had an old 1993 Ford Crown Victoria with a doughnut spare. I opened the trunk when I was cleaning it out to sell it 2008 and the spare had exploded. The spare had never been used, still had the little rubber nubs that are on a new tire. Don’t remember the brand of the spare for sure, Michelin I think. Went to the Junk, er, Recycling Yard for a replacement, about $20 I think. Rims aren’t reusable and tire store couldn’t get a replacement tire.
You didn’t ask Peter if he had driven up to a high altitude during the summer months.
Perhaps he filled it to its Max and then went over the Rockies or something and the tire couldn’t handle the pressure.
The rubber manufacturer’s association (http://www.rma.org) offers this advice:
Normal, natural aging of a tire, as well as ozone in the air, may cause the rubber to crack, especially in the sidewall area. Tires should be checked for this condition or other damage before every long trip. Tires over five years old or ones that show signs of cracking should be inspected regularly by a tire professional to determine if they should remain in service or be discarded.
Did anyone else find it unusual that the caller wanted to know if we should go back to the vehicle dealer or the tire dealer? This was a 10 year old car with a decidedly used TEMPORARY spare!
RODENT DAMAGE! A nice chewy rubber spare in a dark space would be irresistible. Look around for “mouse scat”.
I’m wary of the words “had” exploded. This would suggest that the tire had a tear, perhaps in the sidewall, or perhaps even carcass fibers showing.
The spare is 15 years old. I find myself wondering if the poster is the original owner and of he had ever checked the spare since buying the car. The sidewall could have been torn by a previous owner on a granite curb (been there, done that) or similar. I’m finding it hard to imagine a spare tire, even a doughnut, exploding. The fibers in the carcass are pretty darn strong and oriented to prevent such an event even when travelling on a 3,000 pound vehicle at 50 mph.
Fairly common for the Firestone donut spares to self-destruct in the Volvo 850’s and 70 series. Several similar reports at brickboard.com and volvospeed.com
My '96 model delaminated in the trunk after 11 years- no damage required. When you replace it, look for a Continental spare which Volvo switched to in the later models. Or better yet, put a full size rim and tire in there.
Nobody asked if he had taken it to an unfamiliar mechanic. I have a 1991 Volvo 240 that had the spare swapped out by an unscrupulous transmission shop. Apparently these spares cost several hundred dollars to replace. The advice to go to a junkyard was solid. I paid $10 for mine.