Fill to vehicle spec or tire spec?

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Well, I see there's been a lot of activity while I was gone - but where to start?

Perhaps the best place to start would be to say that one of the reasons I started (and continue) to post on the internet is that there was (and is) a lot of mis-information floating around about tires - and this thread has a bunch of it. Also, it is easy to make a statement about something than it is to either back that up (or refute it) with solid evidence. My web site was designed with that purpose in mind - to save me from having to write the same thing over and over again!

OK, the first issue:

Originally Posted By: TacticalDriver
......On you tube there are only three video clips that are trying to show something, and none of them are made by the tire industry:

Talking about tire stress:
http://www.youtube.com/watch?v=nmo_dkNZIHM

........


Here's one of the first comments to the video - from the guy who posted the video:

"This is standard tire force&moment test performed at Calspan TIRF (Buffalo NY). This particular test is undriven & not braked (the belt drives the tire rotation). The squeal is from the supersonic air bearing nozzles under the belt to provide belt support during the very high vertical force application. It is a standard test run on tires to collect data for computer simulations of rollover and other attempted maneuvers. The load case here is still only 3/4 of max load of such a tire."

Calspan does a lot of tire testing - both for the tire industry, the automotive industry, and others such as the Federal Government.

The purpose of the machine (and the test) is to characterize the behavior of tires under various conditions - unltimately leading to a computer model of the tire, which can be used for a ride and handling computer model of a vehicle. You can go through a lot of variables in a hurry when you use computer modeling. An extremely useful tool!

I recognize the test sequence as a sweep of slip angles. If you watched the video, the first step in the test was a high load. That was to warm the tire up. That was followed by a lighter load with the slip angle being changed continuosly with data being collected on a real time basis.

Technically, Calspan would be part of the tire industry. BTW, I know that many the major tire manufacturers have this type of machine (my office used to be 100 feet from one!) as does Ford and GM and I assume other vehicle manufacturers as well.

Originally Posted By: TacticalDriver
........and none of them are made by the tire industry:

.......

Handling related to the tire pressure
http://www.youtube.com/watch?v=5r6gV2JWI0I

..........



Obviously this is a vehicle test done on a handling course. The question is whose? There aren't any obvious logos or signage to tell us - BUT - At the end of the video there is a brief image of the Michelin logo and something being said in French. I take this to mean this is an official Michelin release - and the last time I looked, Michelin was part of the tire industry.

I could go on, but I hope you see my point: The information you are providing is faulty to the extreme - and I haven't bothered to discuss the srticle written by Sgt. Storton - which is also just chock full of errors.

Your whole premise seems to be built up on a series of faulty and error filled statements - both from you and from others. You're not doing a very good job of supporting your position with evidence. Here's a good example:

Originally Posted By: TacticalDriver
........That Tire and Rim Association paper is listing the MINIMUM pressures for each load. MINIMUM.....


If you read the table it says "Tire Load Limits at various cold inflation pressures" That means the load is a maximum, not the other way around!

But you went on quaoting from Tire and Rim:

Originally Posted By: TacticalDriver
......"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. .......


There is a nuance here that isn't expresed very well in the book - and that is that those pressures are "permissble".

But more importantly, what goes on in actual practice? Are tires tested at these elevated inflation pressures?

Only for the speed rating test. EVERY other test conducted on tires refers back to the load table and not to the Notes on page 1-34.

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

If you haven't concluded by now that you're working off a set of bad assumptions, let me state it clearly. It takes a lot of work to refute each and every argument you present - but I have.

However, you have yet to back up this statement as I asked:

Originally Posted By: TacticalDriver
.....Although you get a smaller contact patch as a result, because of a higher friction (due to higher weight per sq inch), you don't lose any grip......


Please take the time to review your position and whether you have adequate evidence to support it.
 
OMG, this thread has drifted from the sublime toward the absurd.
Applied engineering is by nature a business of compromise.
Your car could be built to last virtually forever, and it isn't.
This is not simply because the makers don't want to kill their own market, it is also because you couldn't afford to buy the car.
Recommended placard pressures are a compromise, involving tire life, suspension component life, fuel economy, handling (which means not simply ulitmate dry grip, but predictability and acceptable rain and winter performance), load capacity and tire life.
In practice, you can sharpen up the handling of most non-performance tires on most cars by adding a little air over placard pressure.
You can air up the rears a bit to make the car feel more neutral.
You may find the ride degradation to be unacceptable for daily use, unless the roads where you live are unusually smooth.
You may also introduce abrupt or unpredictable breakaway behavior as the limits of grip are reached, particularly in the wet, where all the excitment happens at lower speeds.
You can get a gentle drift going in smooth corners in the wet, for example, while you'd probably not attempt it in the dry.
Anyway, after years of playing around with pressures, I usually just go 2-3 psi over placard, to provide some buffer.
Anything more is usually too much for a street driven car.
I speak from no more expertise than that acquired in many years of driving many different cars.
If you want to put a bus up on two wheels, for example, I can't help you.
 
Please don't lecture me on physics - I have a degree in astrophysics...that's why the points made by the engineers on BITOG (like Capri Racer and Shannow) make sense to me. Sure, most of the driving public doesn't consider pressure or vehicle dynamics...most of them don't even check the tire pressure at all! But there are people who do check, and there are people who engineer vehicles and tires. You are arguing a contrary position to a tire engineer that works on these...really? ...really?

I note that your experts are drivers, with degrees in the humanities...or no stated degrees at all...and you wonder why I side with the engineers?

Just because you have driven this way doesn't mean that it's safe or reasonable. If you drove without incident while your seatbelt was unbuckled, drinking coffee in one hand and your i-phone in the other, for 200,000KM, I would not adopt your method....it's very likely that you were just lucky...not that you've "discovered" a better way. Just because a guy with a Master's degree in education drives this way doesn't mean that it's safe or reasaonable...In another thread, I'll be happy to discuss safety, and error management, in the operation of complex equipment in demanding environments...

Performance improvements observed in a Crown Vic on the track while performing "tactical driving" are interesting but not necessarily applicable to the real world, any more than my experience with extreme maneuvering in the Tomcat is applicable to a Boeing in commercial service.

Trust me, you wouldn't want to be a passenger on a plane in which I applied my techniques of tactical flying or in which I made up my own set of limitations that disregarded all the testing and engineering that went into the creation of the aircraft flight manual and its published limitations.

Your heirs and their attorneys might like it...but you wouldn't, and no one should be exposed to that kind of risk...and yet you're insisting that we should all adopt your method of anectdotal evidence, ignoring engineering and analysis because you think you've discovered a better way or some "secret" that the manufacturers and engineers "hid" from us???

Oh please....this truly has become absurd...
 
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Originally Posted By: Shannow
But you are advocating operating ABOVE that safe Max aren't you ?

i.e. in the uncharted area of the safety factor.


People...if we don't know what is the bursting point (breaking point) we can not pinpoint the SAFE MAX.

No one knows for sure, there is no documentation, there are no test reports or physical tests done in this regards by the tire industry, or if they are they are no made public, to show that 5-10 PSI over the sidewall max is not safe.

In the tire history, there is not a single incident recorded referring to a street incident where a tire "exploded" due to an over inflation.

I am using myself 10 PSI (on the dot) over the sidewall max, and in those years I had small and big cars, training cars.

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..."
 
Originally Posted By: Astro14
If you drove without incident while your seatbelt was unbuckled, drinking coffee in one hand and your i-phone in the other, for 200,000KM, ...

Now that's a stupid (very stupid) thing to say and make this assumption. It sounds like you know me or you have seen me driving or you have been to the same race track with me!

That proves that even an astro physicist can behave like a Hilly Billy.
 
Originally Posted By: CapriRacer

Talking about tire stress:
http://www.youtube.com/watch?v=nmo_dkNZIHM

Here's one of the first comments to the video - from the guy who posted the video:

"This is standard tire force&moment test performed at Calspan TIRF (Buffalo NY).

Calspan does a lot of tire testing - both for the tire industry, the automotive industry, and others such as the Federal Government.

The purpose of the machine (and the test) is to characterize the behavior of tires under various conditions - unltimately leading to a computer model of the tire, which can be used for a ride and handling computer model of a vehicle. You can go through a lot of variables in a hurry when you use computer modeling. An extremely useful tool!


I know that many the major tire manufacturers have this type of machine (my office used to be 100 feet from one!) as does Ford and GM and I assume other vehicle manufacturers as well.



What I was trying to demonstrate with that video clip is that there is a technology in place to safely test every theory ve ever discussed here.
On that machine would take absolutely nothing but some time and some tires to prove or disprove that driving with overinflated tires is dangerous or not.
You overinflate a tire you mount it on that machine, you apply a given pressure and.. .. let it roll.

You said you had a machine 100 m away from your office.. .. and no one ever in the tire history had the curiosity to perform an overinflation test (and publicize the results)

How hard can that be?


Originally Posted By: CapriRacer

Obviously this is a vehicle test done on a handling course. The question is whose? There aren't any obvious logos or signage to tell us - BUT - At the end of the video there is a brief image of the Michelin logo and something being said in French. I take this to mean this is an official Michelin release - and the last time I looked, Michelin was part of the tire industry.
That was a handling test not a tire safety and/or integrity test


Originally Posted By: CapriRacer

I haven't bothered to discuss the srticle written by Sgt. Storton - which is also just chock full of errors.


Such as?



Originally Posted By: TacticalDriver
........That Tire and Rim Association paper is listing the MINIMUM pressures for each load. MINIMUM.....

If you read the table it says "Tire Load Limits at various cold inflation pressures" That means the load is a maximum, not the other way around!

But you went on quaoting from Tire and Rim:

Originally Posted By: TacticalDriver
......"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. .......


There is a nuance here that isn't expresed very well in the book - and that is that those pressures are "permissble".

But more importantly, what goes on in actual practice? Are tires tested at these elevated inflation pressures?

Only for the speed rating test. EVERY other test conducted on tires refers back to the load table and not to the Notes on page 1-34.



Two ways of saying the exactly the same thing. Max load for a given pressure has exactly the same practical meaning as min pressure for a given load. The chart then has the note that the tire engineer can increase the pressure up to max psi without increasing the load and this difference is what the engineer has to work with when determining recommended pressure. ie, NVH vs performance, which usually means leaning towards soft and squishy so john Q public does not feel or hear the road.

Please note they call it recommended pressure not required pressure, or some such, because there is no safety issue in going above the recommended pressure. If there was you can bet the NSHTA would have long ago had a placard with that in big bold letters. In fact it could well be that higher than recommended pressure is safer as it gives more crisp steering response and better cornering traction. We already know for a fact that higher pressure means better hydroplaning resistance.
 
Originally Posted By: CapriRacer

Originally Posted By: TacticalDriver
.....Although you get a smaller contact patch as a result, because of a higher friction (due to higher weight per sq inch), you don't lose any grip......


Please take the time to review your position and whether you have adequate evidence to support it.



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.

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".

My dear friend, I am not trying to challenge you or dismiss your years and years of experience. This would be more like you challenging me on the driving course ( I said driving course not racing track).. . LOL!!!!
But listen.. .. I am more than willing to get together for in one weekend and put all the theories to the test
 
Tactical driver,

Let’s talk credibility for a moment – as in, you have none.

You post 3 links and say none of them are from the tire industry, and yet every one of them was – and it only took a few minutes to determine that.

And now you want us to believe that a taxi fleet has done what you are advocating with no negative results? Pu-lease!

Every time you post, you display it more and more. Please stop before you become the Harold Camping of BITOG
 
Originally Posted By: CapriRacer
Tactical driver,

Let’s talk credibility for a moment – as in, you have none.

You post 3 links and say none of them are from the tire industry, and yet every one of them was – and it only took a few minutes to determine that.

And now you want us to believe that a taxi fleet has done what you are advocating with no negative results? Pu-lease!

Every time you post, you display it more and more. Please stop before you become the Harold Camping of BITOG

w0w, Talk about someones credibility taking a dive.
CapriRacer you lose.
Filing your level headed responses in the delete bucket.
way to go capri, way to go.

Thank you TacticalDriver, from a Fellow Hyper-Inflator with more than positive results, Jim
 
Originally Posted By: TacticalDriver
Originally Posted By: Astro14
If you drove without incident while your seatbelt was unbuckled, drinking coffee in one hand and your i-phone in the other, for 200,000KM, ...

Now that's a stupid (very stupid) thing to say and make this assumption. It sounds like you know me or you have seen me driving or you have been to the same race track with me!

That proves that even an astro physicist can behave like a Hilly Billy.


I didn't make an assumption, or an accusation. I gave you a hypothetical example as an analogy.

While my degree is in Astrophysics, I'm a fighter pilot.
 
Originally Posted By: TacticalDriver
Originally Posted By: CapriRacer

Originally Posted By: TacticalDriver
.....Although you get a smaller contact patch as a result, because of a higher friction (due to higher weight per sq inch), you don't lose any grip......


Please take the time to review your position and whether you have adequate evidence to support it.



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.

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".

My dear friend, I am not trying to challenge you or dismiss your years and years of experience. This would be more like you challenging me on the driving course ( I said driving course not racing track).. . LOL!!!!
But listen.. .. I am more than willing to get together for in one weekend and put all the theories to the test



In Newtonian physics, friction is the result of the normal force times Mu, the coefficient of friction. Your discussion is not Newtonian physics...

Vehicle dynamics are more complex...but simply stated, the interaction of the tire area and road surface are both factors. Reduction in that contact area reduces grip, plain and simple, all other factors being equal.

The excessive sidewall flex to which you refer doesn't happen in all vehicles, only the ones on which you have based your position. There are a lot of good, high performance car/tire/chassis set-ups in which the over inflation strategy you are espousing will actually reduce grip.

Ask anyone that tracks their car. The best grip comes when the temperature across the tire surface is even, meaning that the whole width of the tire is being put to good use. That takes trial, track time, and measuring...the kind that the tire and vehicle manufacturers do extensively before a new product is sold. (My BIL is a GM engineer by the way...they test cars for millions of miles before releasing them to the public...)

The best grip doesn't just come from hyper-inflation...it comes from appropriate inflation for the conditions. You can't simply state a blanket recommendation of X PSI over sidewall - that fails to take into account the vehicle on which the tire is installed and its actual use.
 
Originally Posted By: AstroTurf
Originally Posted By: CapriRacer
Tactical driver,

Let’s talk credibility for a moment – as in, you have none.

You post 3 links and say none of them are from the tire industry, and yet every one of them was – and it only took a few minutes to determine that.

And now you want us to believe that a taxi fleet has done what you are advocating with no negative results? Pu-lease!

Every time you post, you display it more and more. Please stop before you become the Harold Camping of BITOG

w0w, Talk about someones credibility taking a dive.
CapriRacer you lose.
Filing your level headed responses in the delete bucket.
way to go capri, way to go.

Thank you TacticalDriver, from a Fellow Hyper-Inflator with more than positive results, Jim


Jim - let's keep this professional and on the subject...shall we?

Part of the issue is credibility.

The credibility of posters like Capri Racer, from whom I have learned about tires, and others, from whom I have learned about oil, is the reason that I frequent BITOG. I appreciate their knowledge of the subject and I am willing to listen.

You and Tactical Driver have pushed this issue, and Capri Racer, hard...

From where I stand, it's clear that you're interested only in winning...if you're interested in learning from those who are recognized experts (like Capri Racer, Shannow, Molakule, to name just a few...) in their particular field, then you'll enjoy this site.

If you're looking to "win" in internet postings...well, then, you won't enjoy it...

I think it's time to ask one of the moderators for a lock...there's no point to this thread anymore.
 
Last edited:
Originally Posted By: Astro14
While my degree is in Astrophysics, I'm a fighter pilot.


Neither of which make you anymore qualified than a Man with Common Sense, Who approaches this undertaking in slow and measurable steps.

But you do a Great Job as a Cheer Leader.

Keep up the Good Work, Jim
 
Just an FYI

The latest issue of Road and Track (July 2011) shows that the air pressure is not equal to the avearge contact patch pressure. Pages 114 and 115!

Sorry, TD, you were wrong again!
 
I agree with you, Astro14. Time to lock this thread, there is no reason for this thread to go on like this. AstroTurf and Tactical Driver ideas are out of whack.
 
Originally Posted By: TacticalDriver


Two of the people advocating 5-10 PSI is Sgt. Dave Storton, the Director of the San Jose Police Academy, and he holds a Master's Degree in Adult Education. He is the lead instructor for the Emergency Vehicle Operations Course (EVOC) at the San Jose Police Academy, and is a lead instructor for the local regional academy. He teaches EVOC instructor courses, advanced EVOC instructor courses, off road EVOC, counter-terrorist / dignitary protection driving, and motion picture stunt driving. Dave has trained over 3,500 drivers.



Show us the link to their written statement advocating the use of pressure 5-10 psi above SIDEWALL MAXIMUM.
 
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.


Taxi companies and drivers aren't interested in maximizing tire life nearly as much as they're interested in maximizing fares. I see lots of taxis in the Toronto financial district every day and 95% of them run their metered axles underinflated so the tires rotate more times per km. Apparently at some point someone with some influence noticed because it even ran on the news as a dishonest practice, but nothing changed.
 
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).
 
Originally Posted By: TacticalDriver
People...if we don't know what is the bursting point (breaking point) we can not pinpoint the SAFE MAX.


I explained to you before that the ultimate failure point of any pressure containment system under a static (and usually full of water to reduce stored energy) has absolutely NOTHING to do with the safe working pressure of a system exposed to a variable environment.

Why do you keep harping on that the bursting pressure has any relevance to safe working pressure ?

You are operating inside the zone that the designer deemed to be the safety factor, for a weak cord, a few clipped kerbs etc....How far in ?

Did YOU design the tyre ?

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.


As an engineer, I typically limit my advice (to my own company and others) to those areas that I have been trained, can provide technical references, and can maintain a defensible position.

If you are "advising" taxi companies to operate outside the OEM deemed safe range, you better have more than anecdotal evidence to back it up, a wicked Professional Indemnity Insurance (that doesn't exclude negligence),and great legal counsel.
 
Originally Posted By: AstroTurf
Originally Posted By: Shannow
But you are advocating operating ABOVE that safe Max aren't you ?

i.e. in the uncharted area of the safety factor.


What is the Safety Factor?

Jim


Jim,
the safety factor is put into a design to ensure that there's margin for all of the things that I mentioned previously.

It's not a range where people should be intentionally treading.

In my professional life, when we see defects in pressure containing equipment, or intend to alter pressures, temperatures, or cycle times, we get a proper design review carried out...by certified, trained professionals
 
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