My Tire Hyper-Inflation Story... What's Yours?

Status
Not open for further replies.
Joined
Dec 28, 2009
Messages
532
Location
Richmond, VA
My name is Jim. I am not a special person. Just a simple man searching for the best bang for my buck.

On April 25th, I put to rest a set of Nokian WR G2 SUV 215/70 16 tires. They served me well for 64,500 miles. They stood tall at about 41psi throughout their lifetime. I replaced them with a set of Michelin LTX MS 215/70 16.

These were placed on my 2005 Chevrolet Astro 8 passenger van. It has been converted/used for work. It's psi placard calls for this size tire and a psi of 38.

Upon the first day of travels at 38psi, I found the van to be very sloppy. On the second day of operation, I began to measure, monitor, and modify the cold psi as well as the hot operating psi.

Within the first 9 days of operation, I conducted at least 27 recorded psi/temp/time measurements. I also decided on the best cold psi for my van/tire combo. I traveled 600 miles during those 9 days, and my average mpg was 17.3.

During the next/last 30 days of operation at my new cold psi standard, I have traveled over 3,100 miles, achieved an average of 18.4 mpg, and recorded another 60 psi/temp/time measurements.

I will say in closing that...
I am very happy with my results.
This is not for those not willing to put in the work, measurements, and monitoring required to make safe decisions.
I have done this with my past sets of tires also.

I believe that...
Neither the vehicle psi placard, nor the tire sidewall max are absolutes, just guidelines/starting points.
Everyone's results/needs will be different.
There is No Simple Calculation that Applies to Everyone.

Your Mileage May Vary, Jim

PS My operating psi is over both the placard and the sidewall recommendations.
 
I know folks, especially hypermilers do go over sidewall values, but Im not sure I would want to. To each their own, but you are cutting into safety margin.

Im surprised that the LTX tires, which seem to get good reviews, made your van so sloppy compared to the Nokians. How high were you pressurizing the nokians?
 
Originally Posted By: JHZR2
I know folks, especially hypermilers do go over sidewall values, but Im not sure I would want to. To each their own, but you are cutting into safety margin.

Im surprised that the LTX tires, which seem to get good reviews, made your van so sloppy compared to the Nokians. How high were you pressurizing the nokians?


Michelin LTX MS is great tire, very comfortable. My third set.

Nokians were inflated to 41psi.

Jim
 
Why people have decided that the maximum tire pressure listed on the tire is optional and only a "guidline / starting point" is beyond me.

I'm viewing this as similar to the modifications made to systems I've designed over the years and folks being angry with me when they fail. I point out that my design predicted the failure mode, and the owner made changes without requesting an opinion, and threats of lawsuits and claims of wonderful benefits from the modifications disappear quickly.

I am not saying that design engineers are perfect - they are not. However, there are often valid reasons for their recommendations that may not be obvious to those whose life does not revolve around that arena.

Best of luck.
 
Originally Posted By: MNgopher
Why people have decided that the maximum tire pressure listed on the tire is optional and only a "guidline / starting point" is beyond me.


Hey, Thanks for sharing.

I don't suppose you have ever exceeded the speed limit either.

Have a Good Day, Jim
 
exceeding an engineering design specification IS NOT the same as exceeding an arbitrary speed limit...exceeding a tyre's rated speed would make a better strawman...and still be dumb not knowing the design parameters and intent of the designer.
 
Originally Posted By: Shannow
exceeding an engineering design specification IS NOT the same as exceeding an arbitrary speed limit...exceeding a tyre's rated speed would make a better strawman...and still be dumb not knowing the design parameters and intent of the designer.


Excess is Excess.

Thanks for sharing, Jim
 
There is a hefty margin in max inflation pressure ratings. Immediately post the Firestone-Explorer blowout rollover case in the '90s, max inflation pressures were bumped up 10% on a wide range of Michelin truck tires. I remember getting a set with a now 110 psi max and was incredulous, as the max was 100 psi just a few weeks before. Research and confirmation from my shops owner revealed the truth.

Bottom line: max pressure limits are conservative. We are long past the era when engineering decided the spec'd limits on physical items in our society. Now it is overwhelmingly the legal dept that decides. Very sad not to be able to trust the specs.
 
Originally Posted By: Shannow
exceeding an engineering design specification IS NOT the same as exceeding an arbitrary speed limit...exceeding a tyre's rated speed would make a better strawman...and still be dumb not knowing the design parameters and intent of the designer.


+1

Eating like [censored] your entire life isn't the same as being genetically "designed" to be susceptible to high cholesterol, heart problems, etc. You may be able to run > sidewall pressures for your entire life, but who's to say you won't eventually run into a set of tires with flaws slightly greater than the design allowance, leaving you on the side of the road at best.

As far as the analysis, I like it. I'm too lazy to do the types of logging you've done, but I always admire those who put in the time.

You're welcome in advance.
48.gif
 
Last edited:
Originally Posted By: dsr70
There is a hefty margin in max inflation pressure ratings. Immediately post the Firestone-Explorer blowout rollover case in the '90s, max inflation pressures were bumped up 10% on a wide range of Michelin truck tires. I remember getting a set with a now 110 psi max and was incredulous, as the max was 100 psi just a few weeks before. Research and confirmation from my shops owner revealed the truth.

Bottom line: max pressure limits are conservative. We are long past the era when engineering decided the spec'd limits on physical items in our society. Now it is overwhelmingly the legal dept that decides. Very sad not to be able to trust the specs.

Yes, they wont publish burst psi because people would run right up against it for FE, handling, or w/e. Then a couple years later as the rubber ages it fails as they are airing it up and kills them.
 
If you live to see the wear pattern alone on grossly overinflated tires, you will re-calculate your 'savings'. Especially on the vehicles with some kind of intricate suspension system that were engineered to work best in a certain range. Safety was mentioned above, and is the concern number one.

Not all amateurs are dilettantes, though..
 
Originally Posted By: Colt45ws
Yes, they wont publish burst psi because people would run right up against it for FE, handling, or w/e. Then a couple years later as the rubber ages it fails as they are airing it up and kills them.


As I've said in the other thread, the ultimate burst pressure means absolutely nothing in a loaded, fatigue experiencing tyre exposed to the environment...as such it's silly to ask for it.

Is the burst pressure of your propane bottle more than the rated pressure ?

Obviously yes.

Without knowing how much corrosion is inside it, what structural flaws exist from manufacture, what batch of steel that it came out of, how far over the rated pressure would YOU happily run and stand your family next to it ?

Your second point is exactly why they are designed WITH a safety factor. To make sure that the operating unknowns don't bring the whole thing unstuck.
 
Originally Posted By: AstroTurf
Excess is Excess.


Overfilling your swimming pool is not the same as exceeding a manufacturer's design rating, or growing your hair too long.
 
I understand the premise. Its OK to cut into the margin of safety designed into a product because the factor of safety exists.

The problem is you don't know all the elements and variables that went into determining where the line was drawn and it isn't always evident to the user that the line has or is about to be crossed.

Its easier to argue that excess is excess rather than citing actual scientific study that shows what you are doing is OK.
 
Originally Posted By: MNgopher
Its easier to argue that excess is excess rather than citing actual scientific study that shows what you are doing is OK.


See First Post.

Jim

PS I will add that in my testing, I did find the point of excess.
 
But you are still not understanding where you are in the design envelope of the tyres, obviously.
 
Do Test Pilots & Engineers always agree?

I am not here to argue with the Book Smart of the forum. Just letting others know what I have found and am doing.

Jim
 
So please explain exactly where you are in the design envelope of the tyre that you are testing ?

WRT all pertinent parameters, not just pressure vs mileage (or whatever)

What reserves are there for parking outside everyday versus garaged, bumpy roads, kerb clipping, the analyses that you have done on the tyres that you are driving on to work out what factory defects exist...

Would love to see your test protocol and your results, being a book trained engineer.

I'm keen to learn...and I truly am, as I hate a day to go to waste not learning something. I don't feel pain being proved wrong, something rare for my breed.

So show me !!!

Steve
 
AstroTurf,

First, thanks for taking a toned down and reasoned approach to the subject. As you saw, the discussion can get quite heated. Here's where I have problems with hyperinflated tires.

Tires have a lot of characteristics:

Dry Traction
Wet Traction
Snow Traction
Mud Traction
Rolling Resistance,
Ride Quality
Handling (and by that I don't mean grip!)
Wear
Durability (and by that I mean long term structural integrity!)
Ability to avoid punctures
Ability to absorb impacts without failure
etc

And applying different tires to a vehicle can make the vehicle feel and behave differently - and there is a whole list of things that ought to be considered.

While you explored a lot of variables, I'm going to bet you really didn't explore the above list to any great depth - and there is the rub.

Vehicle manufacturers and tire manufacturers HAVE explored tires operated at the placard pressure - and while there are still gaps in their knowledge - and gaps in their ability to fix certain problems - they at least have enough knowledge about where those problem areas are.

So why don't tire manufacturers and vehicle manufacturers get knowledge og high pressures by testing at those pressures?

For one, the vehicle manufacturers have made it quite clear that the loss of ride quality is unacceptable and they are not going to go there!

Another is that IF there is a segment of inflation pressure practices that need to be explored, it's operation UNDER the placard pressure. This is probably 1,000 times more prevalent than the opposite. It's also the one that will cause more structural failures.

To give you a feel of the magnitude of the problem: Dr. Sanjay Govindjee, a professor at the University of California - Berkeley in January 2001 wrote a paper about the problems with the Firestone ATX's and Wilderness AT's - the ones that prompted the huge recall. He wrote the paper at the request of Firestone and while some may say this was self serving on the part of Firestone and is probably shaded, for those of us who know the subject of tires well, it has the ring of truth.

In that report Dr. "Govindjee said: "Overall, it is noted that the problem at hand is rather complex, the failure rates are fractions of a percent, and thus determining a single cause for the tire failures is an unrealistic expectation."

The key point is failure rates in fractions of a percent.

At the time this report was published, every tire manufacturer was under heavy scrutiny by the federal government - and the company I work for was no exception. I was keenly aware of the failure rates for the tires my company produced (I still am!)

The value - even though it is vague - totally lines up with what I know (but can not reveal) to be true.

Let's assume the actual value is ½%. That means out of 200 tires in service, only 1 failure is expected - and that failure rate is considered to be very bad!

So how many tires do I need to test - how big a population do I need - to be able to say that something involving tire failures is "safe? Well, I'm not much of a statistician, but my colleagues who are tell me it's in the range of 100,000 tires.

That, my friends, is why one individual's experience should have so little impact. Even a taxi fleet doesn't have a large enough population to say anything definitive. - and I haven't even mentioned that problem of comparing 2 populations.

To this end, for the last 2 years I have been recording anecdotal internet reports of tire problems when the tire are highly inflated. So when someone says "It's perfectly safe!", I know that not to be true and can back that up with evidence! I have plenty of reports of center wear, plenty of reports of blowouts, traction problems, ride issues.

Do I have enough to say that it is worse - or better - or the same - as placard inflation pressures? No. But I now know that no one else does either.

That is why I take a very hard stance with anyone who advocates using inflation pressures above the sidewall pressures.
 
Steve,

This is not a training session. It is just a reflection of what I have done/am doing.

If someone wants to learn anything more than what I have shared, then they will have to do their own leg work.

Perhaps you should get started. Let us know how it goes for you, as you are far more able to put it into Engineering Terms than I.

Thanks, Jim
 
Status
Not open for further replies.
Back
Top