Unsafe Pressures in Filling Tires.

When filling up a passenger car tire, at what pressure does one run the risk of over inflation and blowing your hand off from a sudden tire explosion?

For the sake of argument, lets say it is a regular tire that says pressure up to 60PSI on the sidewall.

In other words, what is the built in safety margin?

I got to thinking about this a while back as I filled a bicycle tire and at less than 60 PSI the rotten (in hindsight...) tire and inner tube blew with what sounded like a shotgun blast. Fortunately it was opposite my hand.

I took care of a fellow once that had a big defect in his face and forehead from an exploding tire/truck rim that nearly killed him and left him brain damaged.

 

High pressure bicycle tires can take 100 lbs or more, but the volume is very small. That's why you have to use short bursts using a gas station type compresser: too much volume and you can blow the tire off the rim.

Car tires typically take 35 lbs and need a comparatively huge volume of air. I don't know where the bursting point is from too much pressure, but they are quite strong and it would take a long time to get a car tire up to 100 lbs. I would venture to say the valve would blow before the tire. The tire your friend had must have had a cut, OR he was already brain damaged to begin with.

Ken

 

He was a patient not a friend and it happened with a big truck tire like on a semi.

 

Well, I imagine they're so big they take a low pressure. But you said 60 lbs? It had to have damage on it already and he was unlucky.

Ken

 

The old semi-rig rims were a 2 piece design, and were very dangerous. Most places had/have a big cage to put them within while mounting or dismounting tires on those rims. They're no longer produced, but there's still a lot of them on the road.

edit: my point being, automobile rims are designed differently, and are less likely to blow on tire mount.

 

The tire that injured the man was probably a large truck split rim wheel/tire. Those are notoriously dangerous to work with. Many people have been hurt and some killed working on those. On the pressure question, tires heat up and pressures increase some as you drive. But I'm sure any tire in good condition can be run at the max initial pressure listed on the sidewall, although that may not be best tire wear pressure. Obviously your margin of safety is lowered, and as tires age you increase risk of a failure. Higher tire pressures usually result in better mpg. But I stick with pressures that are recommended by the vehicle mfgr, and monitor tire wear if I think some adjustment is needed.

 

On really big tires, like large trucks, earthmovers, etc., OSHA (I believe) stipulates that they be enclosed in a cage during inflation. Quite a few people have been killed by these when they explode. Maybe these were all the old split rim type.

Regarding car tires, I wouldn't trust the valve to let go before the tire does. For sure, I would not venture beyond the max. inflation pressure that the mfr. specifies. (Why would you, anyway?) A car tire might not be as lethal as a larger one, but it could sure hurt and/or blind you.

 

Large over the road truck tires run typically around 100 psi. Some are being used at up to 120 psi (gage).

Many folks are maimed or killed working on semi tires and in particular the split rim versions that are know to be very dangerous. Failure of a split rim has been know to take peoples heads off....

Go to a shop that works on semi tires and you will find a cage that they put the tire in while inflating it. Also note how the cage is all distorted from tires blowimg up inside of it. Your patient was probably lucky to be alive if he was working on a semi tire when it exploded. Most who are doing so with out the protection of a cage don't live to tell about it.

When teaching my son to drive I explained the damage that can be done by an exploding semi tire and taught him not to run along side the wheels of a big rig on the highway. If you have ever seen a semi tire explode on the road you would understand the amount of energy involved here.

 

The rated maximum pressure is printed on the tire. Don't bet your life on an extra "safety margin.

The maximum rating is usually far more pressure than you'd want in the tire (unless you really want to reduce the contact patch to an inch down the middle of the tread).

That said, my tire pump has a clip on filler, and I move out of the direct line of fire before turning the pump on. Justin Case.

 

Many years ago I brought a new tire and mag wheel to a gas station(mistake) to have it mounted and balance. I dropped both off and came back a few hours later to pick them up and found out the person mounting the tire was at the hospital. Apparently the tire wouldn't seat on the rim and he keep adding air to it, finally it blew ripping the tire. Turns out he was lucky and wasn't hurt bad which is a good thing. Tire had about a 4 inch tear on the side wall.

 

Back in the late 60's I was at Elkhart Lake for the old Road America 500. We heard what sounded like an explosion and found out that at the Goodyear trailer one of the tire technicians was mounting a race tire when it let go. They flew him out, but unfortuantely he did not make it. Nochance that the valve stem would give before the thin walled Blue Streak of the era. My motor home tires take about 110 lbs and they recommend that you not stand near the tire when filling.

 

Split rim wheels/ tyres should only be inflated in a cage!

Many years ago I owned a few Firestone stores and remember the story of a farmer that was filling the tyres on his farm tractor. One of the split rings blew off of a wheel and cut him in half.

 

+1 Most tires say "Max pressure 44lbs". Most consumers mistake this to mean that is how much air you should put in them. No, this is very dangerous. Not only can the tire explode and fail, but the tire exploding could cause a lot of problems like rollovers and such. Most cars/trucks on the road should have around 30lbs in them. Also, it's equally dangerous to put too little air in them. Remember all the Ford rollovers? It was caused by Ford wanting them to set the tires to 26lbs because they were softer. Too little pressure caused the tires to fail and the trucks to flip at hwy speeds. I witnessed one such accident recently personally. Never wanna see that again. If you drive a diesel truck, especially dullies and the lifted trucks with huge tires you might be running 50-60lbs.

 

http://www.alberthaviation.com/TireCageVideos.htm

Aviation wheels, but graphic example of why to be careful.

 

I was never that concerned with the tire itself but more the magneisum rims giving way. Kind of a catch 22 as if one greases the tire to pop on the bead easily, the tire will rotate on the rim under a hard acceleration. Found to be a big problem on the 550 rear tires / rims as I quit using the water / soap combination due to the moisture and resulting pressure increases once the tire got hot.

Finally found a product that remained slippery when exposed to air but dried up and became very sticky once air was excluded and the tire was on the rim. Used to take around 100 PSI to seat the bead on some of the short sidewall tires before that anaerobic product was found. I would hook up a tire fill hose, set the regulator to 90 PSI and move away from the wheel. Usually would pop on the bead just about the time I forgot about it and scare the blazes out of me. Never had one break the wheel but I have seen the carnage from when one did.

Dave

 

aircraft rims are a split rim also. we use nitrogen and put them in a metal cage to fill them after a tire change. rim halves are ultra sonic inspected at set tire changes intervals to look for cracks. we service the main tires to 180 -200 psi. blowing one apart with out a cage has killed people.

 

Almost everyone that mounts car tires over inflates them to get the bead to seat and then bleeds them down. I'd say it's very common for them to inflate them to at least 45 lbs or more on a car tire designed to run 34 lbs.

 

I used to mount tires when working towards college. When a bead wouldn't seat, we had an inflatable belt that went around the outside of the tread to try to help seat the bead without over-inflating.

Of course, this was way back when gas was 35 cents a gallon, so we weren't dealing with 40 series tires.

 

I wish I could clearly remember the story, but I heard this about 40 years ago. It seems that my grandfather had a small shop in Iowa that sold and serviced Maxwells (I think that's right). The shop hand was inflating a tire (probably from a tractor) and it exploded, throwing him through the wall of the shop and into the parking lot.

 

The inflatable band just spreads the sidewalls out against the bead so it will hold air. Once they hold air it's another story to get the bead to seat. I'm sure once they removed the band they over inflated the tire to get the bead to pop into place. Once that happened they reduced the pressure back down to normal.

Most of your accidents people are talking about had to do with the split rims. For anyone that does not know what they are they are different from a car rim. A car rim has a lip on the inside of the rim and the outside. The lip of the rim is what the sidewal pushes out against and it is also the part they used to clip the wheel weights onto. On a split rim the inside of the rim has a lip but the outside lip of the rim sort of clips onto the rim like a circlip or E-ring. To mount the tire you would slip the tire on the rim by had and then lock it in place with this ring by expanding it and letting it clip onto the rim. Once the tire was inflated there usually wern't any problems but sometimes when you were filling them up the ring would come off the rest of the wheel with enough force to take your head or your arm off. You where only supposed to fill these inside of a special U shaped cage with a remote air chuck that clipped onto the valve stem so you didn't have your hands inside the cage. If you look at some of those tire trucks on the highways that replace tires on the big trucks you will still see most of them still have the cage on the back of the truck for filling the split rims. The idea was you could mount a new tire on a rim without a machine. You used a special maddox or pick axe to break the bead loose and then you would remove the ring by hand. I unfortunatly had the thrill of mounting split rim tires at a part time job in high school.

Don't try this at home!! The other trick if the inflatible band didn't work to get the sidewalls to spread out enough to hold air was to spray a nice film of lighter fluid inside the tire and throw a match at it but even after that you still needed to over inflate the tire to get the bead to seat all the way.

 

I was driving down I40 toward Memphis one time with a semi right behind me. My windows were down, cassette tape playing, everything fine. Suddenly I heard what sounded like a stick of dynamite go off from somewhere. Kaaaaa...BLAMMMMM!!!!
I didn't know what had happened. I looked all around me, checked my dash gauges, listened to the engine,....everything was fine. I looked in the rear view mirror and saw the semi truck put on his turn signal and start to pull over as one of his tires was ripping to shreds. He had a semi-sized blow out and I was right in front of him. NOT a pleasant experience.

Did they really use lighter fluid or STARTER fluid (ether) to set those beads? Lighter fluid isn't really as explosive or expansive.

 

You never made a tennis ball cannon with lighter fluid when you were a kid? Lighter fluid as in something you put into your cigarette lighter not the stuff you start your charcol grill.

 

Starting fluid is what I use. At 6000 ft elevation it no longer works as well but but back in the midwest it would take a tire, loose on a wheel, set both beads and inflate the tire to 20 some pounds.

I still use it for all the trailer and tractor tires when not near a compressor at home. There is always a can of it on the tractor.

Dave