Fill to vehicle spec or tire spec?

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Originally Posted By: Craig in Canada
Originally Posted By: TacticalDriver


Not so common knowledge:
Lateral grip increases on an (what you would call overinflated and I would call "overinflated")tire, but not because of a change in the shape of the contact patch. Friction is a purely reactive force vectoring in the opposite direction of the force applied. The reason you get better lateral grip is due to the fact that the slip angle of tire is reduced in direct relationship with the reduced deflection of the side wall.
In other words, the higher the PSI the less flex and roll of the rubber compound, thus the better traction.

If you don't believe 320 years of Newtonian physics, just refer to the "handling" video clip and see that despite a higher PSI and implicit smaller contact patch, the vehicle has a better traction due to a more rigid rubber compound.
The lower the PSI more deformable the contact patch, hence less "grippy".


In all higher forms of racing (like Formula 1) tire pressure is reduced in order to increase grip. Compliance creates grip. To increase grip you 1/ decrease tire pressure 2/ decrease spring rate 3/ reduce the diameter of your anti-roll bar. To decrease grip you 1/ raise tire pressure 2/ increase spring rate 3/ increase the diameter of anti-roll (this is why adding or enlarging a rear sway bar will dial understeer out of a street car).



Race car tires are nothing like passenger (street) tires.
They use different rubber, different tread (or lack thereof) and are designed with different life expectancies. So there is no comparison.
Race tires have a Cut Breaker (or Cut Belt construction) that performs very well in regards to the stability over bumps and feedback on odd surfaces
 
No amount of talking, calculating, designing and chatting on the forums, and generally speaking no amount of theory will substitute the practical experimentation. I am not trying to convert anyone to use high PSI, and if anyone does follow my advice, I will have no financial (or political) gain.

I know I have over 200,000 km driven on tires inflated at 10 PSI over the sidewall max, I know other people and organizations doing the same.

I don't have to prove anything to anyone, because I am not trying to convince anyone of anything, again...I will have no gain or benefit either way.

As you could see I just got here on this forum few days ago, looking for a very, very specific answer, namely when, who, where was the first one to affix the placard with the manufacturer recommended PSI.
http://www.bobistheoilguy.com/forums/ubb...588#Post2275588


CapriRacer was kind enough and tried to answer my question to the best of his abilities, and from his answer I gathered that the placard values are based on a 40 years old methodology.

There is nothing else to say. I spend a great deal of time on the driving pad and race track and very limited time in front of the computer. For the past 3 years I drive Vancouver - Las Vegas - Vancouver at least once a month (yes Crown Vic P71 with P225/60R16 tires @50 PSI) and I have never ever have a mishap.


If any of you have the interest of meeting some time and putting to the test any driving theory I will be more than happy to oblige.

All the best and happy foruming. I gatta go put some rubber on the asphalt
 
TD,

Here is where I am having a problem: Every time you post, it contains a falsehood. Here's an example:

Originally Posted By: TacticalDriver
.....This is a common knowledge:
Contact patch area is a function of car weight and inflation pressure. Regardless of the tire width or diameter, the pressure in p.s.i. x sq.in. of contact area x 4 = vehicle weight.......


This is incorrect and here are 3 sources (of many) that prove it to be incorrect:

1) http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

2) Evaluation of the Contact Pressure Distribution of a Rear Combine Tyre on a Hard Surface by P. A. Misiewisc, et al, presented at the 28th Tire Society Conference in Akron, OH, USA, Sep 15 and 16, 2009.

I know this paper wasn't published at the time it was presented to Tire Society, but it so clearly demonstrates that the formula is wrong, I just hope someone can help me find a copy on the internet.

3) The July 2011 issue of Road and Track I cited in an earlier post.

***************************************************

Since you haven't got the fundamentals right, what makes you think you've got a good grip on anything else? Especially when you are talking about areas outside the envelope. I've explained why the burst pressure is not something that has value - except as confirmation that the theory works - and it does. As I pointed out, the company I work for doesn't even do burst testing anymore. They are confident they have a good handle on strength calculation and its affect on fatigue.

https://bobistheoilguy.com/forums/threads/my-tire-hyper-inflation-story-whats-yours.155414/

In this thread, I discuss my reasons why I argue so strongly about the use of high inflation pressure. Bottomline: Not enough knowledge - and what knowledge we have says there are areas of real concern.

Here's another:

Originally Posted By: TacticalDriver
.........CapriRacer was kind enough and tried to answer my question to the best of his abilities, and from his answer I gathered that the placard values are based on a 40 years old methodology......


No, you misunderstood.

Placards appeared about 40 years ago. The best information I have indicates a regulation required them. Before that, the inflation pressure specification was not in an easy to find location - and just recently, it was standardized to the driver's door area, because even that wasn't good enough.

But the methodology about WHAT pressure appears there is under constant revision (Not the question you asked, but I answerecd it anyway!)

Originally Posted By: CapriRacer
......I have documented 3 increases in load carrying capacity of tires over the intervening years. One was the result of the oil embargo on about 1973 - for fuel economy resaons. Another was in the 1980's - and I suspect this was the result of what is sometimes called "tire saturation" - fully loaded tires have non-linear force and moment characteritics when heavily loaded.

And the last increase was the result of the latest Ford/Firestone situation - about 2002 to about 2006.

.........


So the placard pressure is NOT 40 year old technology. It is current - and just like you've said it should be, it is based on over forty years of experimentation by some of the finest people involved in tires and vehicles. It should not be dismissed lightly.

But if you do, you need to really do your homework. Let's take your taxi fleet for a moment. Did they catalog the removal reasons for the tires? Were there are accidents - especially accidents where traction might be an issue?

There are folks doing exactly that for the tire manufacturers - conducting comparison tests - and they write detailed - and proprietary - reports. There is no reason why someone who truly believes that there is something to this high inflation pressure thing can not conduct a test on their own - but they need to be thorough!

But don't expect the tire manufacturers to conduct those tests. These tests are expensive and the vehicle manufacturers have made it abundantly clear they are not going to go there!
 
Last edited:
Originally Posted By: CapriRacer
TD,

Here is where I am having a problem: Every time you post, it contains a falsehood. Here's an example:

Originally Posted By: TacticalDriver
.....This is a common knowledge:
Contact patch area is a function of car weight and inflation pressure. Regardless of the tire width or diameter, the pressure in p.s.i. x sq.in. of contact area x 4 = vehicle weight.......


This is incorrect and here are 3 sources (of many) that prove it to be incorrect:

1) http://www.performancesimulations.com/fact-or-fiction-tires-1.htm

2) Evaluation of the Contact Pressure Distribution of a Rear Combine Tyre on a Hard Surface by P. A. Misiewisc, et al, presented at the 28th Tire Society Conference in Akron, OH, USA, Sep 15 and 16, 2009.

I know this paper wasn't published at the time it was presented to Tire Society, but it so clearly demonstrates that the formula is wrong, I just hope someone can help me find a copy on the internet.

3) The July 2011 issue of Road and Track I cited in an earlier post.

***************************************************

Since you haven't got the fundamentals right, what makes you think you've got a good grip on anything else? Especially when you are talking about areas outside the envelope. I've explained why the burst pressure is not something that has value - except as confirmation that the theory works - and it does. As I pointed out, the company I work for doesn't even do burst testing anymore. They are confident they have a good handle on strength calculation and its affect on fatigue.

https://bobistheoilguy.com/forums/threads/my-tire-hyper-inflation-story-whats-yours.155414/

In this thread, I discuss my reasons why I argue so strongly about the use of high inflation pressure. Bottomline: Not enough knowledge - and what knowledge we have says there are areas of real concern.

Here's another:

Originally Posted By: TacticalDriver
.........CapriRacer was kind enough and tried to answer my question to the best of his abilities, and from his answer I gathered that the placard values are based on a 40 years old methodology......


No, you misunderstood.

Placards appeared about 40 years ago. The best information I have indicates a regulation required them. Before that, the inflation pressure specification was not in an easy to find location - and just recently, it was standardized to the driver's door area, because even that wasn't good enough.

But the methodology about WHAT pressure appears there is under constant revision (Not the question you asked, but I answerecd it anyway!)

Originally Posted By: CapriRacer
......I have documented 3 increases in load carrying capacity of tires over the intervening years. One was the result of the oil embargo on about 1973 - for fuel economy resaons. Another was in the 1980's - and I suspect this was the result of what is sometimes called "tire saturation" - fully loaded tires have non-linear force and moment characteritics when heavily loaded.

And the last increase was the result of the latest Ford/Firestone situation - about 2002 to about 2006.

.........


So the placard pressure is NOT 40 year old technology. It is current - and just like you've said it should be, it is based on over forty years of experimentation by some of the finest people involved in tires and vehicles. It should not be dismissed lightly.

But if you do, you need to really do your homework. Let's take your taxi fleet for a moment. Did they catalog the removal reasons for the tires? Were there are accidents - especially accidents where traction might be an issue?

There are folks doing exactly that for the tire manufacturers - conducting comparison tests - and they write detailed - and proprietary - reports. There is no reason why someone who truly believes that there is something to this high inflation pressure thing can not conduct a test on their own - but they need to be thorough!

But don't expect the tire manufacturers to conduct those tests. These tests are expensive and the vehicle manufacturers have made it abundantly clear they are not going to go there!


My dear friend,

For some reasons you sound (to me) like a pharmaceutical company representative.
Them representatives are super nice, very polite and extremely willing to help, up until someone is raising a doubt. As soon as someone is trying to question the practices or effectiveness of a drug, they start to flame up their nostrils, hoof and puff and start to push bunch of papers, so called "clinical trials", come up with bunch of so called "researches" by some "reputable" what else.. .. doctors ( with vested interest in the drug industry), etc, etc.

When the people die or are the victims of a side effect, the pharme says: "oooopssss, we thought it was safe"

When you talk to the doctors about the natural remedies they will say something similar to what you just said: "the company I work for doesn't even do burst testing anymore"

When someone is pointing to a herb as having the capacity alleviate a certain medical conditions, they say something similar to what you just said:"Since you haven't got the fundamentals right, what makes you think you've got a good grip on anything else? "

In other words I am the only specialist around here.. .. what the f... do you know, who do you think you are to challenge me and the army of engineers working for my master?


All I am trying to question and dispute are the following facts:

1) The current standard for passenger car tire load tables are 40 years old

2) Those standards need to be changed so that would reflect the modern technology

3) If those standards are to be changed, an increase in tire inflation will occur that will conduct to a better fuel economy, longer life of the tire, safer driving.

4) This is not an impossible task or out of tire/car manufacturer's capabilities.

5) Tire industry ( as pharma industry) is full of [censored] politics and they are pushing their political/economical agenda by all means.

6) If a tire is capable of holding 250 PSI, I see no reason it can not be used onLoad @ 50 PSI


As for the Contact patch area is a function of car weight and inflation pressure you and your source ( that you are using over and over and over( and over) again), most likely written by one of your tire engineers friends, are TOTALLY wrong.

If you want we can open another thread on that and analyze it from the physics and dynamics point of view. But I warn you, that is my domain and your tie might get a wrinkle or two.

With best regards,


TD


P.S. Anytime you want to take it to the track or driving pad.. .. let me know.
 
A tyre supporting a car is NOT a free frictionless piston, and therefore the tyre assembly and construction do not translate 1:1 for contact pressure versus inflation pressure.

From my previous link, construction of the tyre changes the relationship markedly.
bias.gif
radial.gif


I can understand increasing the pressure in a bias to get the loaded tread flat, and it's exactly what my neighbour used to do on his bias trailer tyres.

As to 250psi burst pressure, that was a commercial vehicle tyre on a commercial vehicle rim...very different to your road car. How can you say that tyres burst at 150psi based on that ?

And I'll repeat, an aging tyre, in a dynamic environment has absolutely nothing to do with a static bursting pressure test.
 
just throwing my iron in the fire here:

http://www.boeing.com/commercial/airports/faqs/calctirecontactarea.pdf

Would be interesting to know whether Aircraft tyres are radial or bias-ply? Bias-ply certainly seem to have an elliptical contact patch and the rule of thumb of air pressure = average contact pressure is OK for pavement and road considerations. For Radials, I feel the variation in contact area is a bit less sensitive to pressure/load. the sidewalls probably take a lot more load in radials than in bias ply. That is, with bias-ply the air pressure controls the contact patch a lot more whereas with radials the sidewalls have enough structure to lessen the effect of air pressure.

Speaking as a layman here with a bit of pavement engineering background.
 
Last edited:
Yesterday I realized I have spent hours responding to this thread - particularly trying to address falsehoods - and they keep on coming. It is clear there is a huge difference in what is believed to be true. I am going to take a different tack and try to get to a fundamental we can all agree on. Since much of this discussion revolves around the sidewall pressure, Let's see if we can come to some agreement as to what it means.

How is the pressure value on the sidewall deterimned?

It's required by law to be there, but does the law prescribe the value? if not, how?

If you have an explanation, how certain are you? Can you back it up with a link? Is the link from an authoritative source? (I mean a mechanic writing an internet column would not be very authoritative!)

So I pose that as an attempt to get to common ground. We can build on that once we have an agreement.

Don't forget, I'm looking for an explanation as to the value of the sidewall pressure and a link that backs up that explanation.

BTW, the link should explain why there are 3 and only 3 pressures used for Standard Load Passenger Car tires - and I'll post my answer tomorrow.
 
Originally Posted By: Shannow
A tyre supporting a car is NOT a free frictionless piston, and therefore the tyre assembly and construction do not translate 1:1 for contact pressure versus inflation pressure.


So from this point are you saying that: The Radial Tire due to its design will maintain its contact patch during different loading of the tire?

Originally Posted By: Shannow
From my previous link, construction of the tyre changes the relationship markedly.


You are refering to this link, correct? http://www.michelinag.com/agx/en-US/products/advantages/bias_radial/bias_radial.jsp

Originally Posted By: Shannow
I can understand increasing the pressure in a bias to get the loaded tread flat, and it's exactly what my neighbour used to do on his bias trailer tyres.


But his inflation techniques are not needed in a Radial Tire due to its flat tread design. Agreed?

Originally Posted By: Shannow
As to 250psi burst pressure, that was a commercial vehicle tyre on a commercial vehicle rim...very different to your road car. How can you say that tyres burst at 150psi based on that ?


I agree that assumtion cannot be made from that example. It was a video representing the danger of welding/repair a mated tire wheel assy. Video link here: http://www.youtube.com/watch?v=HiLeji8bLOk

Originally Posted By: Shannow
And I'll repeat, an aging tyre, in a dynamic environment has absolutely nothing to do with a static bursting pressure test.


Perhaps. Would you also agree that tires that were used in this test only failed while underinflated? Video here: http://www.youtube.com/watch?v=5r6gV2JWI0I

I will go on to add the third video that TacticalDriver posted a link on. From my limited knowledge it is of a Slip Angle Test. I assume by the comments that this is a test for all tires. I would further add that at the end of this test the tires are still very much usable. I have added another vid which shows basically the same test from a different angle. Videos here: http://www.youtube.com/watch?v=nmo_dkNZIHM
http://www.youtube.com/watch?v=W8UiE7yvO_M&NR=1

I in closing I hope this may help shed a fuller light on today's tire construction, and make others aware of the fact that the Radial Tire of Today holds a flat tread in even the most extreme conditions compared to yesteryear Bias Ply Tire.

Jim
 
Last edited:
Originally Posted By: Shannow
A tyre supporting a car is NOT a free frictionless piston, and therefore the tyre assembly and construction do not translate 1:1 for contact pressure versus inflation pressure.

From my previous link, construction of the tyre changes the relationship markedly.
bias.gif
radial.gif


I can understand increasing the pressure in a bias to get the loaded tread flat, and it's exactly what my neighbour used to do on his bias trailer tyres.

As to 250psi burst pressure, that was a commercial vehicle tyre on a commercial vehicle rim...very different to your road car. How can you say that tyres burst at 150psi based on that ?

And I'll repeat, an aging tyre, in a dynamic environment has absolutely nothing to do with a static bursting pressure test.


Who said that based on the 250PSI (but they were more like 280psi) tires are bursting at 150PSI?!?

"aging tire"??? no one was making any assumptions on an aging tire.
 
You stated that tyre manufacturers need to tell us the bursting pressures, so that educated people such as yourself could choose a "safe" pressure.

Sorry, 150 was a typo...my bad...I meant 50psi, as per your "safe" 50 based on the 250 (or 280...on the truck tyreon the E350 looking rim) in the vid...being the fraction of the bursting pressure that you propose.

You're not assuming that a tyre ages?

Then how can you be arguing bursting pressure as a parameter ?

How can you be advising taxi fleets to raise static pressure on anything other than brand new tyres, subject to no loading, ageing or dynamic stresses...without accepting the environment that they are designed to operate in ?
 
Originally Posted By: AstroTurf
Videos here: http://www.youtube.com/watch?v=nmo_dkNZIHM

Jim


Now Jim... .. you tell me how hard would it be to perform a similar test four sets of tires with the following settings:
1) 32 PSI or whatever pressure recommended on the Door jamb
2) 42 PSI or whatever sidewall max PSI
3) 5 PSI over the sidewall max
4) 10 PSI over the sidewall max

Take the load values of an X vehicle per each tire, apply that pressure and...let it rip
After which lets compare the data and looking for thread wear, structural integrity, noise ratings, vertical firmness, damping, rolling resistance for fuel consumption, etc, etc.

Why don't they do that? Or if they did, why no reports have come to light?

That is the question?
 
TacticalDriver,

Let's look at the vid, and the info we have about it.

It is a side slip test. The tire/wheel combo have been inflated to placard pressure for a Saturn vehicle for which the tire/wheel fits. It is a very severe test, but yet it does not damage the tire in any way. I would add that I have never seen any Saturn vehicle tire/wheel inflated to placard pressure have that flat a tread (think load).

Now having said all of that, I assume this test could represent a single tire on a vehicle being loaded with the entire vehicles weight. Makes sense right?

We do not get this info from the Engineers on this site because it is a trade secret. That's fine. I am a common man with common sense.

Hang Tough, Jim
 
Originally Posted By: CapriRacer
Yesterday I realized I have spent hours responding to this thread - particularly trying to address falsehoods - and they keep on coming. It is clear there is a huge difference in what is believed to be true. I am going to take a different tack and try to get to a fundamental we can all agree on. Since much of this discussion revolves around the sidewall pressure, Let's see if we can come to some agreement as to what it means.

How is the pressure value on the sidewall deterimned?

It's required by law to be there, but does the law prescribe the value? if not, how?

If you have an explanation, how certain are you? Can you back it up with a link? Is the link from an authoritative source? (I mean a mechanic writing an internet column would not be very authoritative!)


And who we can consider... authoritative? Who have the most credibility? A tire engineer? A tire marketing person?

My dear friend, everyone (well... everyone that have been around (circled) a car 3-4 times) knows this car/tire/road interaction is the most complex of all vehicle dynamics influencing systems.

We have all those aerodynamics, energy transfer, thermodynamics, mechanical Newtonian, Amontonian, Columb laws and forces geometry change, chemical reactions between rubber/asphalt, rubber/air, rubber heat, non-linearity, etc, etc, that are not only that interacting with each other but depending on each other.

Do we agree on that?

However, very few people master all or any of those sciences.
What is left? Experimentation. Thru trial and error we can determine how things work, how they suppose to work or how they don't work. We might not be able to explain them from the scientific point of view, but we can get an idea based on common sense on how they work.

We can pretend we have all the answers, but we know very well.. .. we don't.

We might be "authoritative" at our place of work, in front of the people that have seen us in person and they know us by name, we might be "authoritative" in front of our students or trainees but here.. .. we are just some nicknames on "bobistheoilguy" trying to learn or teach a thing or two, spend or waist 20-30 minutes a day.

With best regards,


TD
 
Have a quick question, (lol!!! my questions are never quick but hey.. .. that's a way of saying)

Does any one know (hint, hint all eyes on CapriRacer) how much would a tire test?

Let's say I want to test 4 different brands with 4 different PSI settings (settings I posted earlier)

How much would that cost and where can be done?
 
Originally Posted By: TacticalDriver

I was advising a taxi company about this method somewhere in US, they tried this on two of their cars for about two months after which it became a norm for all 40 vehicles they have.

this is the 3rd year they are using it. Never ever anyone reported a problem, on the contrary the drivers and very satisfied. The only people that were unhappy were the tire vendor.

So I have my personal experience with that. No one can tell me is dangerous or unsafe.

Please someone prove me I am wrong. I mean physical proof not "I think...", "In my own opinion...", "I've heard..."


I hope this said Taxi company will have enough liability insurance covering any accident that happens and lawsuit that follows. Even if I would ride that on my own car I wouldn't tell someone (especially in the US) in the transportation business to do that to the fleet.

I'd get some fuel economy tires inflated to 2-3 psi above placard than high performance tires 5-10 psi above sidewall.
 
Originally Posted By: TacticalDriver
What is left? Experimentation. Thru trial and error we can determine how things work, how they suppose to work or how they don't work. We might not be able to explain them from the scientific point of view, but we can get an idea based on common sense on how they work.


Do the people riding in your cars acknowledge that they are riding in an experiment, where the tyres are inflated 10psi over manufacturer deeemed maximum and sign a waiver ?

Do the taxi passengers acknowledge that they are part of an experiment, riding in a vehicle with purposely overinflated (manufacturer's recommended maximum),and sign a waiver ?

Under the recommendation of a bloke who acknowledges no expertise in tyre design ?

Do the general public know that you are carrying out an experiment on public roads, by purposely exceeding a manufacturer's recommended max ?

I think it incomprehensible that a knowledgeable person would expose others to risk as a part of their "experiment" in direct contravention of industry standards.
 
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