hyper inflation: let's cut to the chase

[ShadeTreeMech]

I just burned up about 4 hours of my life trying to sort the facts from the fiction in this thread and other related sites and threads concerning putting more than the placard recommended tire pressure (NOT SIDEWALL MAX) in your tires.

The gist of what I got is this

1. tires are safe to sidewall pressure. But past 44 psi your valve stem might leak pressure.

2. a tire pressurized to max sidewall will likely last longer and not deteriorate at all compared to a tire at OEM recommended pressure for your car (usually 32 psi) but people who sell tires would rather you don't know that.

3. tire mfg companies are in bed with petroleum companies because they both rely on the same raw material. So why would a tire company give you a cheap and easy way to cut into their profits as well as the profits of their partners in the petroleum industry?

4. If I inflate my 50 psi max inflation tires to 50 psi, I should expect a bit more slipping under low traction situations (snow, ice, dirt, rain). But if I'm hypermiling, I wouldn't be pushing that envelope anyway, would I?

5. radial tires will NOT wear out in the middle more than the sides due to inflation to max sidewall psi. Tires on the rear of rear wheel drive vehicles will do this, but due to it being rear wheel drive, not inflation pressure. Front wheel drive tires will likely wear evenly on the front, while the rear tires will harldy wear at all. This also comes from personal experience as a recovering lead foot with many a mile behind me.

6. Don't buy cheap, Korean, or Chinese tires. They have higher failure rates.

The ONE official article I found (and can't find again) indicated that a radial tire will not blow up until it gets to 150 psi, and even then it would require high speed antics to finish the job. So a 50 psi tire set to 50 psi is as safe as you can get. a 44 psi tire to 50 psi is still likely very safe. a 32 psi tire to 50? Meh, you should spend more money on tires mate!

There is much discussion concerning how race car tires deteriorate in these threads. PLEASE, for the love of all things holy, RACE CAR TIRES ARE NOTHING LIKE PASSENGER VEHICLE TIRES!!!!!!!!!!! They use different rubber, different tread (or lack thereof) and are designed with different life expectancies. So there is no comparison. If you drive a car like it's a race car, expect your treadlife to diminish. But having your pressure at sidewall max isn't going to change much. If anything, underinflation is the anti christ, while max sidewall psi is an innocent baby.

While I don't have any technical data to back up these claims, reading as much as I have concerning tires and applying logic to the missing bits, I believe this rant is as balanced a viewpoint as I've seen yet. Put your tires to max sidewall, drive like you want to squeeze every last foot from each drop of petrol, and you'll be fine. But endless debate is only going to confuse the uninitiated. So if you have something to say contrary to this bit of common sense, prepare to prove it immediately!!!!

[mcrews]

couple of thoughts:
I have run Kuhmos 255/45/18 Exsta asx on my Infiniti Q45 since 58,000 miles. I now have 195,000. I have never had a problem caused by a poor quality tire. They balance perfectly and I rotate every 5k. I get 40k+ a set. They are also quite.

I think that for true (I don't give a crap about anything but that last 1/10 of a gallon) hypermiling you can pump it up to 90psi.....who cares...the car will drive like and ride like crap. Frankly for real world around town driving 39-44 is just as good. At somepoint your are driving with bricks for tires and the wear on the suspension parts just can't justify the very little gain in mpg. Now if your asbout to hit the highway for the next 4-10 hours.....higher psi might be justified.

But hey, don't mind me......... I was told by someone on this furom that ecomodding a Q45 made me an 'obvious Ugly American' and I should do my part and buy a pos micro,sub-mini-compact w/ no a/c and get rid of the Q.

yeah.....right.......

[VegasDude]

Don't forget about Nitrogen. They use it in airplanes. That means you really need it.

[CapriRacer]

There is a lot of contradictory information concerning inflation pressure. But rather than go through it all, allow me to select a single subject and present the other side. It's not that this is the only thing that I could take issue with. It's that this is just one that suits me at the moment:

Originally Posted by ShadeTreeMech

......3. tire mfg companies are in bed with petroleum companies because they both rely on the same raw material. So why would a tire company give you a cheap and easy way to cut into their profits as well as the profits of their partners in the petroleum industry?.........

This implies that the tire manufacturers are deliberately under-estimating that load carrying capacity vs inflation pressure characteristics.

Here’s a page from the Tire and Rim Association Yearbook that shows the design standard for some passenger car tires:



Here it is full size:

http://www.barrystiretech.com/2005traloadtable.jpg

Notice that the pressure operating range is 26 psi to 35 psi.

Vehicle engineers use this book to select the tire size and the pressure that will carry the load of the vehicle, plus a bit more (good engineering practice). They are required by law to put this information on a sticker on every vehicle they make. This means there are going to be severe consequences when they get this wrong - as the recent Explorer controversy demonstrates.

Tire manufacturers, on the other hand, want to produced the least expensive tire that gets the job done - and since they are designing to the same table......

So it becomes a coincidence, rather than a conspiracy, that passenger car tires will burst at pressures well above the maximum sidewall pressure. There must be something else that causes this - and that something is fatigue.

At this point, I could go into a long discussion about fatigue and how it applies to tires, but I don't want to get too far off Point #3. You can look up fatigue on Wikipedia to see where the discussion would go.

[dcb]

Originally Posted by mcrews

hypermiling you can pump it up to 90psi

There seems to be a point of diminishing efficiency returns on PSI, nobody is advocating 90 PSI that I know of, more like 45-55psi. Lets make sure we keep that much straight.

I'm not wild about the term "hyperinflation" either.

[ShadeTreeMech]

I just think hyperinflation sounds funny myself

I agree, 90 psi is crazy hard, and you'd have to replace the whole car after it rattled itself to death. But going to max sidewall ought to be the closest thing to a compromise between OEM over cautiousness and hypermiling lunacy. I've ridden in a truck with tires pressurized to 80 psi, and it's unpleasant to say the least.

So according to that chart, no passenger tire manufacturer even thinks about finding out how a 50 psi tire inflated to 50 psi handles itself? And while I don't think there's a blatant conspiracy going on in the petroleum industry, I suspect the bean counters quietly dismiss anything that could lead to a loss in the quarterly earnings. If I were an executive of a tire company, i would likely do similar things to make sure i still sold a lot of tires. Heck, I'd sponsor tire burnout competitions. But to say that a tire manufacturer doesn't keep certain information to itself (such as longivety of tires at sidewall pressure, and how high they can go without blowing up) would be counter to common sense and ignorant of the issues of capitalism. (No, I'm no proponent of socialism, just there are occasionally bad sides to everything.) And why wouldn't a tire company allow and encourage the myth that tires past the placard pressure are dangerous?

There is simply a lack of evidence that 50 psi in a 50 psi rated tire is a bad thing.

[CapriRacer]

Originally Posted by ShadeTreeMech

......So according to that chart, no passenger tire manufacturer even thinks about finding out how a 50 psi tire inflated to 50 psi handles itself?.......

I hope you realize that these so called 50 psi tires could have been labeled 35 psi tires. That's because of the "notes on page 1-34".

I discuss that about 1/3 of the way down:

Barry's Tire Tech

The 50 psi is a permissble usage - and it should be obvious that the intended use for this pressure is high speed operations - and when tires are tested to those conditions, it is in the context of high speed operation.

But when vehicle manufacturers are specifying inflation pressures, they are in the range of 26 to 35 psi - at least in the US. In that context,it doesn't make a lot of sense to test outside that range - particularly given that this is the design standard and not some usage table.

[SVOboy]

Originally Posted by dcb

There seems to be a point of diminishing efficiency returns on PSI, nobody is advocating 90 PSI that I know of, more like 45-55psi. Lets make sure we keep that much straight.

I'm not wild about the term "hyperinflation" either.

I thought we decided hyperinflation would be used only for ridiculous pressures like 90 psi, or do you still have a problem with it in that context?

[dcb]

that's fine, but not what shadetree meant, based on his sidewall max observations.

I also don't put me running 35 psi tires at 45 in the hyper category, since the 35 psi figure is so conservative to start with.

so there is some grey area certainly, but I would put 90 psi on a ~3000 lb car in the hyper category. and ~50 psi in the higher pressure category.

Main issue IMHO is john Q will think of tires as perfect balloon analogies where more psi will be bad, and anything with the term hyper is reckless.

[orange4boy]

That Tire and Rim Association paper lists the MINIMUM pressures for each load. MINIMUM. Then in a note on the very next page it states this:

Cold inflation pressures may be increased above those applicable to the tire loads up to the maximum marked on the tire with no increase in load.

In other words up to max sidewall is perfectly safe. Black and White from the Tire and Rim Association.