Fill to vehicle spec or tire spec?

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Originally Posted By: Astro14
I'm with Capri Racer on this whole discussion, see my original post...

Tactical Driver is advocating extreme pressures for extreme usage...in his application, which is not unlike taking your car to the track, it makes perfect sense...

But not for me and for the other 99.9% of the driving public.


Both your first post and now this... Your last statement on the issue are full of contradiction.

Further trying to get a straight answer from the "Local Expert Capri Racer" is next to impossible. I have seen his reference to his own little web page dropped so many times that it is not even funny. Always without a specific answer given.

Please, Test and Observe what you and the so called local expert are saying is right, then compare what others have to say. You may learn something.

The MFG is Right... Not always.

People with real life experience (Measured Results) are right. Trust Me.

Jim

PS Riddle me this Joker:
Vehicle MFG recommends vehicle tire size, Observed.
Vehicle MFG also recommends a max PSI of 38
Tire MFG has a max PSI of 35
Whom do I follow?
What say you contradicted experts?
 
Originally Posted By: AstroTurf
PS Riddle me this Joker:
Vehicle MFG recommends vehicle tire size, Observed.
Vehicle MFG also recommends a max PSI of 38
Tire MFG has a max PSI of 35
Whom do I follow?
What say you contradicted experts?

Which vehicle and what is the specific tire size in question?
 
Originally Posted By: Quattro Pete
Originally Posted By: AstroTurf
PS Riddle me this Joker:
Vehicle MFG recommends vehicle tire size, Observed.
Vehicle MFG also recommends a max PSI of 38
Tire MFG has a max PSI of 35
Whom do I follow?
What say you contradicted experts?

Which vehicle and what is the specific tire size in question?


05 Chevrolet Astro Van
P215/70 16
Michelin LTX MS
 
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I looked it up under the fitment guide at work, and it does indeed say:
Cargo Van P215/70R16 99S 38-38 psi
Passenger Van P215/70R16 99S 35-35 psi
 
Originally Posted By: AstroTurf
Further trying to get a straight answer from the "Local Expert Capri Racer" is next to impossible.


Go back to CapriRacer's post on fatigue data versus bursting data...

It is spot on in an engineering context.

Cyclic applications you almost never worry about a single static application, nor infer that an overly stiff static structure will do well in fatigue.
 
Originally Posted By: Shannow
Originally Posted By: AstroTurf
Further trying to get a straight answer from the "Local Expert Capri Racer" is next to impossible.


Go back to CapriRacer's post on fatigue data versus bursting data...

It is spot on in an engineering context.

Cyclic applications you almost never worry about a single static application, nor infer that an overly stiff static structure will do well in fatigue.


PoppyCock...

Another Expert pointing to an Expert?

Does anyone have more than an Engineering paper that they point to? Real life experience?

Common Sense says that a tire inflated to the MFG PSI or ABOVE will have less wear from cycling. it also runs cooler than a lower inflated tire. The prize is there for the thoughtful user of better than MFG PSI. But, You must pay attention to detail to make it happen. 5 to 10 PSI over MFG is NOT going to cause more wear on the tire.

Now go back and answer the Riddle, Joker. Oh, and there ain't no pointing back to the so called experts either. They don't have the answer.

Jim
 
Do what thou shalt is the whole of the law ?

That's not facts and data, upon which this site is based.
 
Originally Posted By: Shannow
Do what thou shalt is the whole of the law ?

That's not facts and data, upon which this site is based.


???

Then show me the tire burst data. At what PSI will a tire burst in Normal Everyday Use.

Thanks, Jim
 
Originally Posted By: TacticalDriver
Can you please explain this?.... Are the standards updated every year or they are the same as 40 years ago?


I hope you'll forgive me for being imprecise when I used the word "Standard".

First, the standards are published in a yearbook for the various types of tire. Needless to say, passenger car tires are designed to a different standard than mining tires, and those are differnt than agricultural tires, etc. Plus there may be different standrads with a given type of tire, delineated by the way the tire size is expressed.

For example: An 11R22.5 is within a family of over the road truck tires and every over the road truck tire whose size takes that form would be built to that same standard (albeit with differences due the size.)

A 295/70R22.5 would be built to a different, but similar set of standards - AND - an 11R22.5 COULD be used on an off road truck and tires designed for that purpose would be built to a different standard than the over the road tryck tire standard.

But once a standard is published, it will rarely change, which is good because a moving target in this area causes all kinds of problem - and that's the case for current standard for passenger car tires - which are called P metrics for the US based standard.

HOWEVER, the load tables will be revised to reflect new tire sizes being introduced (usually by a vehicle manufacturer) - and sizes will be taken off after a period of time when the tire size is long out of production.

And that is what I was trying to say when I said that the standard doesn't change, but it is revised yearly. I was using the word "standard" to mean both the formula and the load table. I should have been more careful.

Originally Posted By: TacticalDriver
.....The idea behind the 5-10 PSI over the side wall max recommended PSI is that you will get a far more precise steering and and not a cushy ride......


What is written on the sidewall of a tire is NOT a recommendation - it is a maximum (if it expresses it that way). You could think of the placard pressure as a "specification" much like the torque on the lug nuts is a "specification".

But I am going to suggest we use the terms "sidewall pressure" and placard pressure" without the modifiers. That way we will have identified what we are talking about witghout expressing a built in prejudice about the meaning.

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......


While I don't normally use this tactic, you have challenged me a couple of times on things I have said, so I feel justified in asking you to back up that statement with data. Not someone's opinion, but numerical results from a test.

Originally Posted By: TacticalDriver
..... As matter of fact......over driving dynamics.


I realize that a lot of the above segment is opinion, and we could quibble over some of this, so I won't go there.

Originally Posted By: TacticalDriver
......C'mon you guys.. .. 5-10 PSI over the sidewall Max PSI is not..."EXTREME".


Here's where I think we run into trouble. Some versions of the Mazda Miata have a placard pressure of 26 psi - and some tires in the size that fits this car have sidewall pressures of 51 psi. I think it is fair to say that using over TWICE that placard pressure would be considered extreme.

OK, That takes care of my responses to Tactical Driver.
 
OK - first, all I have ever said is use the vehicle manufacturer recommendation as a starting point and adjust from there as needed. I personally adjust from the manufacturer pressure as needed, but find that the recommendation for my Volvo (29F, 29R unloaded, 35F, 38R loaded) is a good range.

Capri Racer is a tire dealer and yeah, that makes him an expert. Me, I am a simple guy who operates machinery for a living...and has a maintenance background. I agree completely that using a pressure twice the manufacturer recommendation, exceeding the rated max on the tire itself, is, in fact extreme and you just became a tire tester. I hope you do those things on a track, not on a public street. I test stuff too, but I don't ask anyone else to take the risk when I do.

To claim that increased inflation pressure (which reduces the footprint/contact patch - that's basic physics) results in increased traction is simply not true. You may get better steering response or cornering(in some specific cases) because of a more stable contact patch, but you have reduced the contact patch, and it is the interaction of the tire compound with the road surface that yields grip. That's why racing slicks have more traction (dry) than all-season/rain tires. I suspect that increasing pressure works well on a Crown Vic or Suburban that wasn't intended for tracking, but there are better methods for a Porsche or other sports car that was intended for that use.

Want a real-world example of increased pressure reducing traction? OK: inflation pressure on the main landing gear of the F-14 was 245 PSI (shore). On the ship, it was 350 PSI. When taking the jet from ship to shore and using the brakes, carrier-pressure tires were noticeably more skittish, easier to slide (or engage Anti-Skid) because they had significantly less braking traction at the increased pressure. Felt it many, many times...and lots of "noobs" blew tires the first time they experienced it...

If more is really better, why not try the Tomcat inflation pressure on your tires...I bet at 350 PSI there would be ZERO sidewall flex, they would run cooler, have an incredibly stable contact patch, and last just about forever...right? Or is that extreme...
 
And now for my responses to AstroTurf:

Originally Posted By: AstroTurf
....Further trying to get a straight answer from the "Local Expert Capri Racer" is next to impossible. I have seen his reference to his own little web page dropped so many times that it is not even funny. Always without a specific answer given.....


2 thoughts: First is that it is important that if we are going to discuss a subject, we need to know about it and we both need to be on the same page. I wrote the web site, NOT with the idea of answering specific questions, but for the purposes of addressing all the mis-information that floats around the internet - and there's a ton of it! The web site is by design verbose and covers a particular topic in much more detail than a specific question requires - but within that verbosity are the answers to many questions - which is why I point to it so often. It saves me a lot of typing (which I am terrible at!)

Second, if you have asked a specific question and I haven't answered it, then point that out. I'll be happy to answer those kinds of questions, if I can. Just be aware that I may point you to my web site, because the answer is there - albeit within all those words.

Originally Posted By: AstroTurf
....PS Riddle me this Joker:
Vehicle MFG recommends vehicle tire size, Observed.
Vehicle MFG also recommends a max PSI of 38
Tire MFG has a max PSI of 35
Whom do I follow?
What say you contradicted experts?


Ah, a specific question! Well, there are 2 possibilities.

a) That the tire in question is a Standard Load, while the placard calls for an Extra Load.

b) That the tire in question has a lower speed rating than the tire listed on the vehicle tire placard.

Remember I said that the placard could be considered a specification? The tire info on the placard also includes a Load Index and a Speed Rating - and that could be considered part of the specification.

- AND -

Like a great many things, there are exceptions to all of that and yours is one of them.

First, if you'll look closely at the sidewall of the Michelins, you see that the pressure listed there is NOT a maximum. It is expressed this way: Max Load 1709# at 35 psi. It is expressing a relationship between the load and the pressure.

Second, it is uncommon for a vehicle manufacturer to use a pressure higher than 35 psi for a standard load tire, but not unheard of. It is also permissible according to the Tire and Rim Assoication under "Notes on page 1-34" as indicated on my web site. Further, the only times I have heard of this occuring is when the vehicle manufacturer wants a certain handling characteristic that he can't get it using something less than 35 psi- and I suspect that is the case here. In some respects you could consider it a last ditch effort to address a problem they discovered very late in the development process and one they couldn't fix using springs, sway bars, shocks, or different tire sizes or many of the other tricks they have employed in the past! It happens, but it is rare.

Originally Posted By: AstroTurf
???

Then show me the tire burst data. At what PSI will a tire burst in Normal Everyday Use.

Thanks, Jim


First, ”everyday use” means placard pressure, and clearly tires do not burst due to pressure under those conditions. They might burst due to road hazard damage, but not due to pressure.

Burst data? You won’t find that published anywhere. Why would anyone want to know what the burst pressure is if they are using pressures well away from the burst pressure? – and if they aren’t, then they will have to accept the results of that decision.
 
Originally Posted By: Astro14
......Capri Racer is a tire dealer and yeah, that makes him an expert......


Actually, I am a tire engineer with one of the major tire manufacturers. The fact that this is not common knowledge speaks to the issue raised by Tactical Driver: While I am employed by a tire manufacturer, I am an engineer first and foremost. I wll point to physics and engineering principles to explain what I think is going on - and if you see me leaning towards bias in favor of tire manufacturers without backing that up with those principles, feel free to point that out. I am more interested in revealing the truth than pushing a political point of view.

I feel the better informed one is, the better decisions they can make. I would hate for someone to get injured - or worse - simply because they thought the understood something - and they didn't, and I was in a position to fix that.
 
Originally Posted By: AstroTurf
Originally Posted By: Shannow
Do what thou shalt is the whole of the law ?

That's not facts and data, upon which this site is based.


???

Then show me the tire burst data. At what PSI will a tire burst in Normal Everyday Use.

Thanks, Jim


Apparently the tire industry spends so much money time and effort into proving (or disproving) something that makes economical sense to them, but there is no record of real life application experiments.

No videos of tire bursting point, tire stress, no long time study/experiments of real life applications. Or if they are any they are kept secret, and we are suppose to take their word for it, we are suppose to believe them just because they are the tire industry, the.. .. specialists.

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

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

Bursting point of a tire that we don't know too much about it, but according to CapriRacer this is a truck tire with a 90 PSI tire wall max pressure
http://www.youtube.com/watch?v=HiLeji8bLOk

Although for the past months I am actively seeking for credible, relevant and unbiased information and/or data in regards to the passenger tires bursting point, I was not able to find.
 
Originally Posted By: CapriRacer
Originally Posted By: Astro14
......Capri Racer is a tire dealer and yeah, that makes him an expert......


Actually, I am a tire engineer with one of the major tire manufacturers. The fact that this is not common knowledge speaks to the issue raised by Tactical Driver: While I am employed by a tire manufacturer, I am an engineer first and foremost. I wll point to physics and engineering principles to explain what I think is going on - and if you see me leaning towards bias in favor of tire manufacturers without backing that up with those principles, feel free to point that out. I am more interested in revealing the truth than pushing a political point of view.

I feel the better informed one is, the better decisions they can make. I would hate for someone to get injured - or worse - simply because they thought the understood something - and they didn't, and I was in a position to fix that.



CapriRacer - I apologize for mis-characterizing your background...I was going off memory, from having read your posts before. From your previous posts, I consider you an expert on tires, and value your opinion on the subject. Knowing you're an engineer simply re-inforces my perception.

For the record (as Shannow and few others know), I majored in Physics...Astrophysics, actually, and appreciate the intellectually rigorous approach...

Cheers,
Astro
 
Originally Posted By: TacticalDriver
but according to CapriRacer this is a truck tire with a 90 PSI tire wall max pressure
http://www.youtube.com/watch?v=HiLeji8bLOk

You seriously can't make out it's a truck tire just by looking at it? When was the last time you've seen a tire and rim of this shape on a passenger car?

Why don't you send an email to the guys that performed this test to verify? [email protected]
 
Originally Posted By: CapriRacer

Burst data? You won’t find that published anywhere. Why would anyone want to know what the burst pressure is if they are using pressures well away from the burst pressure? – and if they aren’t, then they will have to accept the results of that decision.


Ha, ha, ha!!!!! That's so mean! We need to know the exact burst point and from there work our way up with the calculations and find a happy median between safety/traction/consumption (fuel economy)/usage depreciation

This i a very common practice called Ultimate Tensile Strength
where the engineers can figure out what is the maximum stress point a material can withstand while being stretched or pulled before.

The testing involves taking a sample of material and in a controlled environment increase applied force until the sample changes shape or breaks.

Why not do the same thing with the tire? Where is the harm on that?
As a SPECIALIST, don't you want to know anything and everything there is to know about your field/service or product?
 
Originally Posted By: TacticalDriver
Originally Posted By: CapriRacer

Burst data? You won’t find that published anywhere. Why would anyone want to know what the burst pressure is if they are using pressures well away from the burst pressure? – and if they aren’t, then they will have to accept the results of that decision.


Ha, ha, ha!!!!! That's so mean! We need to know the exact burst point and from there work our way up with the calculations and find a happy median between safety/traction/consumption (fuel economy)/usage depreciation

This i a very common practice called Ultimate Tensile Strength
where the engineers can figure out what is the maximum stress point a material can withstand while being stretched or pulled before.

The testing involves taking a sample of material and in a controlled environment increase applied force until the sample changes shape or breaks.

Why not do the same thing with the tire? Where is the harm on that?
As a SPECIALIST, don't you want to know anything and everything there is to know about your field/service or product?


You are mis-understanding what he is saying. They do test to ultimate load, but they don't publish it...

Boeing doesn't publish the ultimate load on the 747, they publish the rated load (it's 2.3G by the way)...Grumman didn't publish the ultimate load strength on the F-14, it was rated at 7.5, then reduced to 6.5 for fatigue life(...though I can tell you from personal experience that it can handle well over 8G...that titanium wing box was strong...)

I find it odd that you are telling an engineer how to do engineering...
 
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Originally Posted By: CapriRacer
...I wrote the web site, NOT with the idea of answering specific questions, but for the purposes of addressing all the mis-information that floats around the internet - and there's a ton of it! The web site is by design verbose and covers a particular topic in much more detail than a specific question requires - but within that verbosity are the answers to many questions - which is why I point to it so often. It saves me a lot of typing (which I am terrible at!)...


With all due respect but on the Barry's Tire Tech is says:
"It is my understanding that copyright laws prevent me from publishing the entire document... but I am allowed to post excerpts with the intent to educate - so I will only give a summary of the parts of the study that will be of interest.

Please note: I am going to show results for each test conducted - regardless of what the results were - in other words a full disclosure - no hidden agenda.

...Some powers that be within the company don't think it is a good idea for people to be posting on the internet. This creates an odd situation for me. On the one side, I have access to a lot of interesting information. On the other side, there is some information that is considered quite proprietary."

Who's interests?

In other words I am allowed only to present aspects that are according to the company policies/politics but nothing that they don't want you to know or be informed about.

I will select the kind of information I want to present you, and makes the case for the tire industry, as for the rest I will say is proprietary or copyright.

Meaning I am only going to tell you half of the truth.

It's like telling someone:
- ...one can stop a knife with his/her chest.
- But he/her died!
- Yeah but I was not allowed to tell him/her there is a possibility he/she can die. Proprietary information
 
No offence, but I think you should listen to Capriracer, I think he's pretty unbiased as he never mentions anything about the company he works for.
As for your "fill near bursting is best" theory, go do some testing yourself. I've had tires at 50psi cold for autocross and they ride like wooden wheels... I wouldn't want to drive them on the street if I was paid to, let alone to make the tires last longer.
I am with you that the car manufacturers suggested pressure can be lower than optimal for handling and maybe tire life, but having passenger car tires anywhere over 40 psi on the street has no advantages at all for you in my experiences.
 
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