Pontiac Bonneville GXP

Tires and Burst Pressure – What Causes Tire Blowout?

I’ve had at least a dozen people come to me worried that if they exceed their manufacturer’s recommendation for tire pressure, that they may be more likely to have a tire blowout. This is not only untrue, but also leads one to be ignorant of the true cause of blowouts.

To start, what is burst pressure?

In my own words, burst pressure is the pressure needed to inflate a tire at which point it will physically burst. Generally speaking, tires will burst at a static pressure of around 200psi. This is a far cry from the maximum sidewall pressure rated on all passenger vehicles. What one needs to understand is that tire manufacturers have factored in a massive margin of safety in tire pressure ratings so that there is no possibility for an expensive lawsuit against them, so if they state you can run 51psi on your tires cold, you will be able to do so safely under normal road conditions. Keep in mind, a massive pothole will be likely to damage your tire regardless of pressure.

What causes tires to “Blow Out?”

In unexpected scenarios, I call this tire degradation. Tires have a “chemical clock” that allows them a finite amount of usable life in years, regardless of how they are stored. A popular showing on the show “20/20” described this issue very clearly. A father had gone to a tire shop to have new tires installed on the family minivan so his son could drive off to Canada for a vacation with his friends after high school graduation. At some point during their visit, they had a tire blow out that caused the death of the driver and all passengers. It was later discovered using the date stamp on the side of the tire that the tire had severely exceeded it’s usable life and should never have been sold.

To re-iterate, this tire blowout occurred out on their family minivan with what appeared to be a brand new tire, indistinguishable from a newly manufactured tire, that was actually manufactured 6-7 years prior and spent that many years on a shelf. The rubber compound on a tire begins to get weaker, more brittle, and loses its structural integrity over the years regardless of whether it’s being used or if it’s been sitting on a shelf. With the exception of defects, massive potholes, large punctures, and other “external causes,” tires generally blow-out only due to age, regardless of pressure.

So, what can I do to prevent a tire blowout?

As if it’s not bad enough that tires degrade on their own, excessive heat will accelerate this chemical degradation. By excessive heat, I’m referring to excessive sidewall flex/rolling resistance-induced heat, not leaving your tires out in the sun (although that does have an effect). You can physically notice a significant change in sidewall temperature between a tire inflated at placard (car manufacturer’s recommended) pressure and the maximum sidewall pressure. An under-inflated tire will not only cause a reduction in fuel economy and handling, but it will also significantly increase the temperature of the tire’s sidewall due to constant flex and resistance, especially at highway speeds. This causes irreversible damage.

To maximize the life of your tires, inflate them to at least the placard pressure. Inflating them higher (but not exceeding maximum sidewall pressure), will help them last even longer, both with regard to tread wear (your mileage may vary) and with regard to chemical degradation.

When purchasing new tires, check the date stamp on the tire to verify that it isn’t an old stock tire. The following article shows you how to check:
Tire Tech Information – Determining the Age of a Tire

Replace your tires once they start to get old, despite how much tread life you may have remaining on that tire. A 7 year old tire is already dangerously likely to have a blow-out. Be sure that the shop where you purchase replacement tires doesn’t try to re-sell your old tires in case they have a decent amount of tread remaining.

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