# Tires and Burst Pressure - What Causes Tire Blowout?



## XtremeRevolution (Jan 19, 2012)

*Tires and Burst Pressure - What Causes Tire Blowout?*​
This is not so much of a question; I figured I'd write this to address some conventional misunderstandings related to tires and tire pressure. I've had at least a dozen people come up to me worried that if they exceed their manufacturer's recommendation for tire pressure and go up to the maximum sidewall pressure, that they may be more likely to have a 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 even the 51psi that the Eco's tires are rated for on the sidewall. 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. 


Moving on to the second part of this topic, *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 "60 minutes" (which can be found on youtube and has been posted here before) 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. I don't recall the exact number, but the tire at the time was 6 or 7 years old. 

To re-iterate, this guy had a tire blow 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*?
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. 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 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. 

If anyone has anything they want to add, feel free to do so.


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## The Wolf Wagon (Mar 5, 2012)

Thanks for this very informative article. I have been following your advise on tires since I first put my ECO in service!


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## obermd (Mar 3, 2012)

I replaced the Bridgestone Blizzacks on my son's Jeep last fall even though they still had almost half their tread life left. Bridgestone recommends no more than 4 years for the Blizzacks and his had been through 4 New England winters already.


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## wbwing (Feb 23, 2011)

That doesn't mean that it isn't a safety concern to fill tires that far past the manufacturer recommendation. Braking distance can increase severly for way overfilled tires. My sister once filled up the tires on my family's car to 60 psi cold because she wasn't thinking. They were relatively new tires and by the time I discovered that something was wrong with the tires, they were swollen, mishapen, and one of the tires had the tread tearing off. Can't tell me those tires weren't going to fail catastrophically sooner than later.


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## XtremeRevolution (Jan 19, 2012)

wbwing said:


> That doesn't mean that it isn't a safety concern to fill tires that far past the manufacturer recommendation. Braking distance can increase severly for way overfilled tires. My sister once filled up the tires on my family's car to 60 psi cold because she wasn't thinking. They were relatively new tires and by the time I discovered that something was wrong with the tires, they were swollen, mishapen, and one of the tires had the tread tearing off. Can't tell me those tires weren't going to fail catastrophically sooner than later.


Nowhere did I recommend inflating them beyond sidewall maximum. However, inflating them up to sidewall maximum is perfectly safe for the reasons I already mentioned above. The tire was designed to operate up to that pressure safely for the life of tire. 

There is a large safety margin for legal reasons in these tires. I simply don't believe that you had the tread tearing off of a tire that was inflated to 60psi as a consequence of the pressure. The only way that could have happened is if the tire was very old to begin with. Because of the metal plies in the tire, they do not change shape or "swell" when inflated until you get to very high pressures that force the metal plies beyond their physical limitations, which is a pressure greater than your typical compressor will allow you to inflate. 

That being said, I'll stand corrected if you can provide any proof, whether it's pictures or documentation. I will stand by my comment that a tire is absolutely safe to inflate up to it's maximum sidewall, and the manufacturer's rating is nothing more than a recommendation for the best balance between ride comfort, handling, and fuel economy. 

Furthermore, I have NHTSA documents that will prove that braking distance will not be affected by tire pressure so long as you are above 20psi. In fact, hydroplaning resistance is improved.


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## wbwing (Feb 23, 2011)

Even if the tire can handle the extra pressure, I still don't think the loss of braking performance is worth a minute gain in fuel economy.


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## coinneach (Apr 10, 2012)

wbwing said:


> Even if the tire can handle the extra pressure, I still don't think the loss of braking performance is worth a minute gain in fuel economy.





> Furthermore, I have NHTSA documents that will prove that braking distance will not be affected by tire pressure


You were saying?


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## wbwing (Feb 23, 2011)

The NHSTA is a pretty reputable source, so I'd like to see that data, but believe you if it says so. Underinflated tires increase stopping distance I'm sure, but I've seen the dangers of over inflated listed on many a faq sheet and articles such as this one:

Dangers of Over Inflating Tires | Hybrid Cars


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## XtremeRevolution (Jan 19, 2012)

wbwing said:


> Even if the tire can handle the extra pressure, I still don't think the loss of braking performance is worth a minute gain in fuel economy.


I should bring up all of the documents that I used in my tire pressure fuel economy thread. It's a long one, and had a lot of resources. I feel like I'm bringing up things that have already been settled. 

To start with, police cruisers use maximum sidewall pressures due to the performance and mileage benefits gained. Greater stability, greater hydroplaning resistance, and it's the same Goodyear Eagle RS-A tire that you get in the retail store. 

To continue, not only do you gain fuel economy, but you also gain ride stability. There's less of a "spongy" feel, making your car more predictable and more controllable in an evasive maneuver. This is extremely important at higher speeds. 

To add to this, you gain tire life. Due to the reduction in rolling resistance, you improve treadwear, and you reduce sidewall temperatures. Due to the weight of the car on the tire, the sidewall is constantly flexing. This causes friction and resistance, which in return creates heat. This heat build-up in the sidewalls of the tires causes an irreversible degradation of the rubber compound, which leads to accelerated dry rot and a higher likelihood for blowouts. 

There is only one significant compromise to increasing tires to their manufacturer (e.g. Firestone, Goodyear) recommended sidewall maximum, and that is ride quality. The stiffer tires will absorb fewer minor bumps on the road. 

Although you can find these with a simple google search, here's the aforementioned document:
TIRE PRESSURE SURVEY AND TEST RESULTS
http://www.google.com/url?sa=t&rct=...uoHgCw&usg=AFQjCNFNMJtDLSByfpklRGwf7qDcjNqR0A
FEA chapter III. tire pressure survey and test results


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## XtremeRevolution (Jan 19, 2012)

wbwing said:


> The NHSTA is a pretty reputable source, so I'd like to see that data, but believe you if it says so. Underinflated tires increase stopping distance I'm sure, but I've seen the dangers of over inflated listed on many a faq sheet and articles such as this one:
> 
> Dangers of Over Inflating Tires | Hybrid Cars


Well, I posted them in my last post. Goodyear also did the same tests. Granted, they didn't go from 35 to 42psi, but they did show the effects of changes in tire pressure, and the effects of continuing an increase in pressure furthers the same trend. 

When you read an article such as this one, you always need to keep in mind that there is a massive amount of misinformation out there, and you need to be critical of many things. This particular article in question is more of a blog than anything, written by an unknown author with an undisclosed occupation. In fact, I'm fairly certain I addressed this article in the other thread I had on this topic in the fuel economy section. The author makes many baseless assumptions on a limited understanding of the topic. NHTSA's and Goodyear's testing would disagree with many of the points he made. For example:



> It should be expected, then, that traction, stopping distance and handling characteristics have been altered to a degree that increases the risk of losing control of the vehicle.


The above does not provide any proof, backup, or logic. It's simply an empty statement. Sure, they've been altered, that's a given, but what indicates that a change is automatically negative? Moving on...



> The elevation of those risks increases the probability that the vehicle will not stop as expected and also increases the risk that the vehicle can become unstable in curves, especially on high speed roads and exit ramps.


Really? He should have checked with his local police department first. They would have told him to get his story straight or keep quiet. The truth is that the higher tire pressures actually increase stability by making the car more predictable and steady on the road.



> Most troubling of all is the increased vulnerability to hydro-planing to which an over inflated tire is exposed. The shorter and smaller the adhesion patch the more vulnerable a tire is to hydo-planing, as a short adhesion patch does not have as much “time” to “squeeze” water into the tread grooves.


The above is plainly incorrect and makes absolutely no sense. A short adhesion patch has a higher pressure to the road _per square inch_, allowing it to "pierce" through the layer of water. This article might explain what I'm talking about:

Browser Warning

I'll end it with the following quote:



> That’s too much if I use my rule of thumb that stopping distance is increased, in percentage terms, by double the increase in air pressure, in percentage terms. Are you comfortable with a 30% increase in stopping distance? Are you comfortable with a 20% increase in stopping distance?


I believe I've made my point. The above article should be permanently removed from the internet. As mentioned before, the testing done by Goodyear and NHTSA (and probably more if I take the time to do further research) is in direct contradiction to his empty claims. His random calculations pulled out of thin air are laughable at best.


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## sciphi (Aug 26, 2011)

This is like 3000 mile oil change arguments. You just can't persuade people who don't want to be persuaded.


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## wbwing (Feb 23, 2011)

touche. I'll concede the point and that you have some solid sources backing up your claims.


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## NBrehm (Jun 27, 2011)

realistically you aren't going to see massive changes in braking distance or massive changes in hydroplaning between a properly inflated tire and max sidewall pressure on most tires. This can change depending on the type of tread pattern and what compounds the tread are made of but for most standard off the shelf over the road tires the changes will be negligible. Biggest threat there would probably be a bumpy road where the increased PSI increases your spring rate and *MAY* make the car bounce, taking weight off the wheels. The big issue with blow outs from increased pressure has nothing to do with the tire just randomly bursting. The danger comes when you hit a pot hole or a curb or any object that a tire with less air pressure may be able to absorb may lead to a blow out because you lose sidewall flex and it becomes MUCH easier to exceed the aforementioned 200 PSI (if that is even the burst point) in one area of a tire.


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## XtremeRevolution (Jan 19, 2012)

NBrehm said:


> realistically you aren't going to see massive changes in braking distance or massive changes in hydroplaning between a properly inflated tire and max sidewall pressure on most tires. This can change depending on the type of tread pattern and what compounds the tread are made of but for most standard off the shelf over the road tires the changes will be negligible. The big issue with blow outs from increased pressure has nothing to do with the tire just randomly bursting. The danger comes when you hit a pot hole or a curb or any object that a tire with less air pressure may be able to absorb may lead to a blow out because you lose sidewall flex and it becomes MUCH easier to exceed the aforementioned 200 PSI (if that is even the burst point) in one area of a tire.


I think a pothole big enough to cause a 44psi tire to burst (up from 32psi, which isn't a lot) would probably bend your rim. It takes a lot to take a tire from 51psi static to 200psi. 

Someone here could probably calculate how compressed one area of the tire would need to be to reach that burst pressure. 

Sent from my Bulletproof_Doubleshot using AutoGuide.Com Free App


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## XtremeRevolution (Jan 19, 2012)

To update this, the video I was referring to regarding blowouts was shown on 20/20. I found it on youtube:

Dangerous Tires - YouTube


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## Mattburgess (May 29, 2012)

Good info.. thanks xtreme


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