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Old 05-29-2008, 05:26 AM   #21 (permalink)
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Hey Ya'll,

I refuse to believe that a tire manufacturer would put a max inflation number on the side of a tire that was higher than it was safe to inflate it to. If it says Max 35 PSI, then that tire better be able to handle that pressure even with high heat conditions or inaccurate guages causing the tire to exceed that number. If it could not handle that then they would be facing lawsuits when the tires failed.

They would obviously design the tire to handle even more pressure than listed on the side to have a margin of safety to take into consideration heat and tire guage variables. This is why people get away with exceeding those max numbers, but exceeding those numbers brings the tire closer to the edge of it's safety margin. The more hyperinflated tires are closer to the point of failure wheather it is a safety or actual tire failure, but only the manufacturers would know how close.

If tire X fails at a certain PSI then they would want to make sure that no one inflates their tires beyond that pressure. They would do this by putting a number on the side of the tire that has a margin of safety big enough for them to feel like tire failure lawsuits would be unlikely. The tire companies would know how big this margin of safety is, but they would not necessarily want the consumer to know because they would be more interested in maximizing profits than maximizing tire wear or fuel economy.

Capriracer, would you agree to these statements? and when can we talk about truck tires?

Later,

Allan Greenblazer

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Old 05-29-2008, 01:43 PM   #22 (permalink)
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CapriRacer -

Quote:
Originally Posted by CapriRacer View Post
I'm starting a discussion thread here - and I'm hoping to move a discussion that got started when I introduced myself:

http://www.ecomodder.com/forum/showt...ires-2522.html

So hopefully this will be a bit more visible and a bit more "on topic".

First, let's define some terms:

Underinflation: Using less inflation pressure than is listed on the vehicle placard (assuming the placard tire size is being used.)

Overinflation: Using more inflation pressure than is listed on the vehicle placard (assuming the placard tire size is being used.)

Hyperinflation: Using more inflation pressure than the maximum listed on the tire sidewall.

Vehicle placard: The sticker on the vehicle that lists the original tire size and the proper inflation pressure for that size.

Agree?

Any other terms we need to define?
I would add :

Maxinflation: Inflating to the maximum listed on the tire sidewall.

I *deliberately* got LRR tires rated at 51 PSI so I could go "pressure to the max" and not worry about violating the sidewall max.

This is a site I reference to others because I think it has a *lot* of good info on tire technology :

The wheel and tyre Bible
http://www.carbibles.com/tyre_bible.html

CarloSW2
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Old 05-29-2008, 04:21 PM   #23 (permalink)
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CapriRacer -

I posted this thread in hopes you would comment :

My Continental Contact-Pro Tires
http://ecomodder.com/forum/showthrea...ires-2642.html

CarloSW2
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Old 05-29-2008, 05:15 PM   #24 (permalink)
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Quote:
Originally Posted by cfg83 View Post
Maxinflation: Inflating to the maximum listed on the tire sidewall.

I *deliberately* got LRR tires rated at 51 PSI so I could go "pressure to the max" and not worry about violating the sidewall max.
I like that definition.
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Old 05-30-2008, 07:13 AM   #25 (permalink)
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I apologize for being silent for the last 3 days, but I’ve been looking for information concerning tire inflation vs various tire properties. I spent a lot of time going through a 700 page publication called “The Pneumatic Tire”. The book is published by NHTSA (National Highway and Traffic Safety Administration) . It is a series of summaries written by various authorities on the subject of tires and tire testing.

So far I’ve only skimmed the articles, looking for graphs and charts that might be helpful, and while I found a lot of stuff that is interesting, I haven’t found anything that deals directly with the subject at hand. I suspect this is because inflation pressure is usually a given in most studies.

I will have to go over the articles again in more depth to see if there are some equations that might include inflation pressure as a term – but wasn’t one of the items studied.

But I suspect that the effect inflation pressure has on various properties was studied long ago and I may be forced into doing searches the old fashioned way – in a library.



Quote:
Originally Posted by Greenblazer View Post
Hey Ya'll,

I refuse to believe that a tire manufacturer would put a max inflation number on the side of a tire that was higher than it was safe to inflate it to. If it says Max 35 PSI, then that tire better be able to handle that pressure even with high heat conditions or inaccurate guages causing the tire to exceed that number. If it could not handle that then they would be facing lawsuits when the tires failed.

They would obviously design the tire to handle even more pressure than listed on the side to have a margin of safety to take into consideration heat and tire guage variables. This is why people get away with exceeding those max numbers, but exceeding those numbers brings the tire closer to the edge of it's safety margin. The more hyperinflated tires are closer to the point of failure wheather it is a safety or actual tire failure, but only the manufacturers would know how close.

If tire X fails at a certain PSI then they would want to make sure that no one inflates their tires beyond that pressure. They would do this by putting a number on the side of the tire that has a margin of safety big enough for them to feel like tire failure lawsuits would be unlikely. The tire companies would know how big this margin of safety is, but they would not necessarily want the consumer to know because they would be more interested in maximizing profits than maximizing tire wear or fuel economy.

Capriracer, would you agree to these statements? and when can we talk about truck tires?

Later,

Allan Greenblazer
Funny you should ask a question this way. I did find something in my searching I didn’t expect:




This an S-N curve for rubber. (Stress - Number of cycles) S-N curves describe the way in which materials behave when subjected to cyclical loading. What these curves say is that the more stress a material experiences, the less cycles it can endure before failure.

S-N curves are very similar for pretty much all structural materials – in that number of cycles before failure is very highly dependent on the stress that the material experiences.

I think this curve is of interest because some discussion has centered around the phenomenon that tires will accept a lot of inflation pressure before exploding. This would be a one-time loading. Just for reference, a passenger car tire would experience 30 million revolutions in 50,000 miles (on the S-N curve that would be 3 x 10^7) If I read the curve correct, at 30M cycles, the stress at failure is only 20 to 25% of that for a single cycle.

Put another way, when a tire engineer is designing a tire, he would choose materials that appear to be grossly over designed. He’s doing that to account for this S-N curve.

That probably also means that hyperinflating tires would result in a fatigue failure many cycles down the road - due to the overall stress in the tire caused by the inflation pressure.


So to answer Greenblazer's question - ah ..... well ...... ah ....... I can't answer it in the form it is in.

The tire is designed around this fatique problem and the bursting pressure of a tire is kind of an incidental property. I haven't seem many tires that have been subject to a "pressure to burst" test, but there are a few videos on Youtube - and there it looks like either the rim or the bead is failing - and most tires fail in the are of the belt package - a completely different area.

But what is going on is that the tire standards organizations have delineated a set of operating conditions (pressure, load, etc.) - and for passenger car tires the operating range is between 1000 and 2500 # (or so), 26 to 36 psi with a provision to allow for higher pressures for special situations, such as high speed operation, and speeds up to the speed rating of the tire (with appropriate adjustments in load and pressure), etc.

So when the tire manufacturers put a maximum pressure on the sidewall of the tire, they are really telling you that this is the limitation they've designed around. So if you exceed those limitations, expect problems since this is an area that the tire manufacturers have not tested in and it may or may not be risky (OK, I think we all know that it is risky, the question is how large is the risk.)

Put another way - the tire manufacturers have warned everyone to stay away from those pressures, so the user assumes liability.

But I can tell you that when tire engineers design tires for higher pressures, they use stronger materials - larger ply cords, more ends per inch, more plies, different materials, etc.) Confounded in this is that uusually the load carrying capacity also goes up, and that's the way a tire is actually used.


Quote:
Originally Posted by Greenblazer View Post
........

and when can we talk about truck tires?.....




Anytime! I just wanted to make it clear that this discussion is about passenger car tires - and other types of tires (truck, aircraft, racing) are different and I didn't want folks to get confused.

So if you want to talk about truck tires, just make it clear. BTW, there are several many different types of trucks - and the tires for each group are indeed different (and delineated so in some way), so please be aware of that when you post.
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Old 05-30-2008, 07:50 AM   #26 (permalink)
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Quote:
Originally Posted by cfg83 View Post
CapriRacer -

I posted this thread in hopes you would comment :

My Continental Contact-Pro Tires
http://ecomodder.com/forum/showthrea...ires-2642.html

CarloSW2
If I have this right, the concern is the car following the grooves in the pavement. We tire engineers call that "groove wander" - although the term "tramlining" is also used (I prefer the former - a bit more descriptive, I think.)

What is happening is that the grooves in the tire are lining up with the grooves in the pavement and when edge meets edge, the tire tends to be follow the edge in the pavement. This phenomenon is going to be affected by the number of grooves in the tire (and the number of grooves in the pavement) and the amount of footprint pressure for each groove.

Obviously over inflating the tires is going to put more pressure on the center grooves - and those grooves will dominate the way the tire behaves. Less pressure will tend to engage the rest of the grooves and decrease the effect.

2 problems: While there are standards about pavement grooving - spacing, width - there are so many non-standard pavement grooving, it is difficult for a tire manufacturer to space the grooves in a tire to account for all of them.

Grooves in a tire are necessary to allow a pathway for the water when the tire rolls through the water - which is what the grooves in the pavement are also doing. In designing a tire, well defined grooves work better that grooves that are interrupted by the tread pattern. Plus the edges of a tread element are areas were the wear will be more rapid that in the center of the element. "Heel and toe" wear is a good examples of this at work. Well defined grooves tend to be more resistant to irregular wear, especially diagonal wear.


In your case, I would try decreasing the pressure and see if that doesn't help.
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Old 05-30-2008, 07:56 AM   #27 (permalink)
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Um Ok... Well CapriRacer,

I do appreciate you responding, but it's a bit of a technical response for me to wrap my mind around. I read it through a couple of times, and I think you are saying that an overinflated tire might or will fail sooner than a properly inflated tire, but not untill it has been stressed past the failure point by lots of use. In other words a new tire might hold higher psi than printed for a while, but with age and use could fail.

Let me simplify and ask again, is it, or is it not safe to run tires at MAX sidewall PSI in your educated opinion? A simple less technical answer would be appreciated.

I don't mean to sound snarky if I am comming accross that way, text can be funny like that. I don't have the technical background to quite grasp what you are saying.

Thanks for your information and participation in this forum.

Later,

Allan Greenblazer

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Old 05-30-2008, 08:56 AM   #28 (permalink)
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Quote:
Originally Posted by Greenblazer View Post
Um Ok... Well CapriRacer,

I do appreciate you responding, but it's a bit of a technical response for me to wrap my mind around. I read it through a couple of times, and I think you are saying that an overinflated tire might or will fail sooner than a properly inflated tire, but not untill it has been stressed past the failure point by lots of use. In other words a new tire might hold higher psi than printed for a while, but with age and use could fail.

Let me simplify and ask again, is it, or is it not safe to run tires at MAX sidewall PSI in your educated opinion? A simple less technical answer would be appreciated.

I don't mean to sound snarky if I am comming accross that way, text can be funny like that. I don't have the technical background to quite grasp what you are saying.

Thanks for your information and participation in this forum.

Later,

Allan Greenblazer
You got it, he is saying that increased pressures reduce the fatigue life, but there is still a huge safety factor there. So the tread will be long gone from the tire before you get to that fatigue failure. If he simplified it in the first place he'd probably catch crap for not backing up his claims and providing technical data/charts.

As for inflating to max sidewall pressure, I think it will be a while till we have more data to support or debunk that. And I feel in the end it will come down to "sometimes", depending on the vehicle/cargo weight, tire load range (this is where where having LT tires will become more of a factor), etc.

I for one don't think max sidewall pressure is always a good idea. Like I said above, it's a "sometimes". My dad used to have a Chevy K2500 (4x4 3/4 ton work truck model). He had me take it in for new tires, they were load range E (same as what came on it stock). The tire shop decided they needed the full 85 psi called out on the sidewall. The ride was horrible. A fairly quick stop in town had the front tires audibly fighting for traction. It was really bad on a washboard road. I stopped in front of a buddy's house and layed a little rubber with a quick stab of the gas. What was revealed was two burnout's probably around 2.5 inches wide each, from 285 series tires (probably around 9" tread width).
Too much pressure + too little weight = crowned tread and very small contact patch

I had a simular experience with a stripped out Toyota pickup I had, weighed in well under 3000 lbs. Built it up with load range E Swampers becasue I had a set of free 16" wheels. Tire shop decided they needed 60 psi after mounting. A single tire's load rating was greater than what my whole truck weighed! When I aired down for wheeling there wasn't any visable buldge in the sidewall untill around 6-7 psi! A little too much tire for the truck!
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Old 05-30-2008, 09:51 AM   #29 (permalink)
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Allow me to shorten:

Quote:
Originally Posted by adam728 View Post
You got it, he is saying that increased pressures reduce the fatigue life, but there is still a huge safety factor there. So the tread will be long gone from the tire before you get to that fatigue failure. ........

I don't think we know how large the "safety" factor is - too many variables. More to the point is that there is an element of statistics involved - tail end of the curve type stuff - that would influence the point at which a failure would occur due to fatigue. As you point out, there's a lot of variables. Things such as speed, road smoothness, etc. would all influence where that point is.

Just as a reminder, when the tire pressure is increased, the wear rate is also decreased, meaning the tire will wear slower - more cycles before removal. This is also going to complicate the situation.



Quote:
Originally Posted by adam728 View Post

.........

I stopped in front of a buddy's house and layed a little rubber with a quick stab of the gas. What was revealed was two burnout's probably around 2.5 inches wide each, from 285 series tires (probably around 9" tread width).
Too much pressure + too little weight = crowned tread and very small contact patch

........
If you watch videos of dragsters, you'll see that the black patch left by the tires is narrower than the full width of the footprint in contact with the ground. This phenomenon also exhibits itself in wear - tire wear on driven tires tends to be more in the center than on the shoulders. You can't see this in FWD cars because the driven tires are also the steering tires - and steering tires tend to wear on the shoulders. But on RWD sedans, for example, the rear tires will wear in the centers and the fronts will wear on the shoulders. Needless to say, this would be aggravated in an unloaded pickup truck where the rear tire pressure is specified for a load in the bed.
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Last edited by CapriRacer; 05-30-2008 at 09:53 AM.. Reason: Spelling, for heavens sake!
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Old 05-30-2008, 10:44 AM   #30 (permalink)
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re fatigue failure:

according to wikipedia "fatigue is the progressive and localized structural damage that occurs when a material is subjected to cyclic loading".

Now what is cyclic loading? In the case at hand, one could probably argue that it happens at every rotation of the wheel at the contact patch, and probably even every time there is a tire warm up cycle. Constant higher pressure does not look like cyclic loading to me, but I might be way off.

From my understanding of it, hysteresis plays the biggest role in tire fatigue. This seems to be demonstrated by the fact that tires which have been run at low pressure for extended periods of time are prone to cord failure and tread separation. So reducing sidewall hysteresis by means of increased pressure would appear like a good way to reduce the occurrence of fatigue failure.

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