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Spare tire explodes

Last month, when it was getting up to 100F in Maryland, my spare tire blew out while it was sitting in the trunk. It even shredded the steel belts in the tread. I had set it to the same pressure as the other tires just a month earlier.

Is this something that happens often? What do people do in the Southwest to protect their spare tires in summer?


How old was the tire? It didn’t explode because of high temp, a tire sitting in the sun in Phoenix is MUCH hotter. There must have been a defect.

The tire must have been defective. What brand is it? If you can bring it to a dealer for that brand, maybe they’ll replace it under the treadwear warranty.

I had this happen with a bicycle tire. I had ridden to my office and the bicycle was parked in a rack outside the building. We had a first floor office and everyone heard a loud pop. We checked around and couldn’t find the source. I found the source when I went to ride home–the back tire had blown.

The spare was around 20 years old. I rode on it for 4 years, and then retired it to the trunk. It wasn’t down to the wear bars yet, but it was getting close. The last time I had a flat and used the spare was around 4 years ago, and it rode fine then.

20 years is WAY past its ‘use by’ date. It died of old age.

That’s your answer. Rubber degrades over time, and twenty years is plenty long enough to have that tire get that bad. Whenever I replace tires on my cars, I have them put the best looking old tire on the spare rim. That way, I don’t get stuck with a spare tire that will shred on me when I need it the most.

It’s also possible that if the spare tire has been run underinflated in those 4 years even one time the sidewall could be thinned out.

Spares likely only have a safe life of 10 year in a trunk UNUSED. This tire lived well beyond its life

Did you check the car body for the presence of a bullet hole? perhaps the car got shot.

That bullet hole scenario is not as far fetched as one would think. I’ve seen 3 cars over the years with bullet holes in them.
One was into the trunk, another was through the glove box/evaporator/firewall/engine mount, and the other was through the drivers door and into the driver’s leg.

The latter was an amazing story. The owner paid a buddy to shoot him one night in an attempt to collect some insurance money. With the shooter and shootee apparently not being on the same page about what caliber gun to use, the shooter used a .45 instead of a .22 and the driver wound up with a permanent limp.

This is not the first over 10 year old spare tire that I have heard of exploding in a trunk well. One LS owner posted some pictures of the aftermath.
BTW, normally, temporary spares are inflated to higher pressures than the rest of the tires. They are rated for about 10 years.
Full sized spares would be inflated to the same pressure as the other tires, but are only good for about 6 years.

I have had this happen to a spare tire. The tires that came on my car when I bought it had tread separation at about 35,000 miles. I kept the one that didn’t separate as a full-size spare, but within about 4 months, it basically came apart in my trunk.

How much wear did your spare tire have? How old was it at the time?

Was the tire ever inflated with a can of "fix-a-flat? Early versions of that product were Butane and quite dangerous. Of course, there would be the question of how it was detonated.

I would almost expect a 20 year old tire to explode. It must have been just a shell of it’s former self.

Rubber has a peculiar property in that if subjected to a stress level just under the amount that will cause an immediate rupture, it will stretch until it fails. Since all tires are subjected to stress by the inflation pressure, it is quite possible to damage a tire, have no apparent effect, but have it fail later. Every so often that failure will occur when the tire is static - like in a trunk. It will seem like a total mystery, but the starting point of the failure occured long ago (often forgot, if even noticed at the time!)

As has been mentioned, age has a major affect on rubber properties - and this is most likely the cause in this case.

" It even shredded the steel belts in the tread."

Radial tires are held together by the belts under the tread. Tiny tread cuts can allow water, sometimes salty water, to penetrate into the belts corroding them and leading to failure. I bet a close examination of the steel cords shows they are rusty and crumbling.