Come one. 60 psi is down right dangerous, and asking for a blowout when hitting a decent pothole. I wouldn't ever recommend that non-sense. And if you're wearing the shoulders like that with 32 psi (likely 2 psi above the door placard), something ain't right, and seems down right fishy.
Uneven tire wear?
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That's a police officer website. Irrelevant to your average driver. They make that clear.
If OEMs, who test the combination of ride quality, handling, braking, and traction, wanted 44 psi, it would be on the placard.
44psi on snow and ice would render your car a hockey puck.
44 psi with the [censored] up roads we have around here from snow and ice would knock your teeth out.
If OEMs, who test the combination of ride quality, handling, braking, and traction, wanted 44 psi, it would be on the placard.
44psi on snow and ice would render your car a hockey puck.
44 psi with the [censored] up roads we have around here from snow and ice would knock your teeth out.
Originally Posted By: Drew99GT
That's a police officer website. Irrelevant to your average driver. They make that clear.
If OEMs, who test the combination of ride quality, handling, braking, and traction, wanted 44 psi, it would be on the placard.
44psi on snow and ice would render your car a hockey puck.
44 psi with the [censored] up roads we have around here from snow and ice would knock your teeth out.
I run about 40 psi in my snowtires, they still work fine, I can see that on hard packed snow or ice less pressure may help but it hurts you in slush or loose snow, since high pressures help prevent aquaplaning then they help driving in slush.
I think the main thing to remember is that you never have the ideal tire or pressure in your tire for the conditions your are driving on, its always a compromise! The best tire on clean dry pavment is a slick, the best tire at 70 mph in the rain is half as wide as best dry tire, etc...
I think the door sticker emphaisizes the comfort factor way too much and it seems dumb to put the tires close to the lower limit of safety when it is common knowledge that people don't always maintain the pressures properly.
Ian
That's a police officer website. Irrelevant to your average driver. They make that clear.
If OEMs, who test the combination of ride quality, handling, braking, and traction, wanted 44 psi, it would be on the placard.
44psi on snow and ice would render your car a hockey puck.
44 psi with the [censored] up roads we have around here from snow and ice would knock your teeth out.
I run about 40 psi in my snowtires, they still work fine, I can see that on hard packed snow or ice less pressure may help but it hurts you in slush or loose snow, since high pressures help prevent aquaplaning then they help driving in slush.
I think the main thing to remember is that you never have the ideal tire or pressure in your tire for the conditions your are driving on, its always a compromise! The best tire on clean dry pavment is a slick, the best tire at 70 mph in the rain is half as wide as best dry tire, etc...
I think the door sticker emphaisizes the comfort factor way too much and it seems dumb to put the tires close to the lower limit of safety when it is common knowledge that people don't always maintain the pressures properly.
Ian
Hey, if it's good enough for the cops, whose lives depend on maintaining control of their vehicles to protect yours, I'm sure not gonna lose sleep at night driving with 45-50psi in my tires. They are running Goodyear Eagle RS-A tires, which are original equipment for the Ford Crown Victoria. Same tires that come with the civilian vehicle. The tires may have a slightly different formulation, but they are passenger tires.
The average driver needs all the help they can get. On this site, I would venture to guess that the majority of us are not average drivers, because average drivers probably don't ponder the mysteries of lubricants the way we do, let alone the square foot or two of contact they have with the road. The average driver is safer riding with higher pressures than with lower.
They are better off starting their tires off at 44psi, and having not checked them, let them dwindle to 32psi over time, than to start at 30-32psi and find themselves at 24psi with slicks.
I know I am in foreign territory running my tires higher then max psi. But I know of a hundred others with millions of miles between them that say it is safe to run tires above the pressure listed on the tire, and have had nothing come of it EXCEPT better wearing tires that get high miles on them, better handling, better protection against hydroplaning, and better fuel economy due to decreased rolling resistance.
The max pressure on the side of the tire simply represents the max load at that pressure, and that increasing your tires above that pressure does not increase the load carrying capacity of that tire. A tire at lower pressure does not have the same load capacity as a tire at higher. That is all that number means on the side of the tire, from my understanding, which I don't believe to be wrong. Is it perfect? Far from it.
As always, YMMV.
The average driver needs all the help they can get. On this site, I would venture to guess that the majority of us are not average drivers, because average drivers probably don't ponder the mysteries of lubricants the way we do, let alone the square foot or two of contact they have with the road. The average driver is safer riding with higher pressures than with lower.
They are better off starting their tires off at 44psi, and having not checked them, let them dwindle to 32psi over time, than to start at 30-32psi and find themselves at 24psi with slicks.
I know I am in foreign territory running my tires higher then max psi. But I know of a hundred others with millions of miles between them that say it is safe to run tires above the pressure listed on the tire, and have had nothing come of it EXCEPT better wearing tires that get high miles on them, better handling, better protection against hydroplaning, and better fuel economy due to decreased rolling resistance.
The max pressure on the side of the tire simply represents the max load at that pressure, and that increasing your tires above that pressure does not increase the load carrying capacity of that tire. A tire at lower pressure does not have the same load capacity as a tire at higher. That is all that number means on the side of the tire, from my understanding, which I don't believe to be wrong. Is it perfect? Far from it.
As always, YMMV.
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Does load capacity refer to weight or to mass?
First, It is unfortunate that the webpage cited above has so many mistakes. I’m only going to address 3 of them. You can draw whatever conclusions you want from there:
1) “The reason the owner’s manual lists 35 psi is because we get the same manual as the civilian version of the Crown Victoria.”
If Sgt. Storton had bothered to go down to the local Ford dealer, he would have realized this is not true – and the difference is enough to account for the extra stuff police vehicles carry (as he mentioned!)
2) "If you look on the sidewall of the tire, you will see that it lists 44 psi max pressure.”
If Sgt. Storton had bothered to look at other police pursuit tires, he would have realized that this is also not true. Some will list 51 psi as a maximum.
3) “ The tires will not balloon out creating a peak in the center portion of the tread when tire pressure is above 35 psi. There is a steel belt that prevents this from happening.”
This is something out of “The Pneumatic Tire” which is published by NHTSA. The book is over 700 pages long and is a compilation of articles written by tire industry experts. This particular chart is supposed to show the size of the footprint relaive to the load an inflation pressure – but it also shows a couple of other interesting things.
a) That lower the load / the higher the pressure, the more the footprint preesure in the center of the tread (and the lower the footprint pressure in the tread shoulders.)
So the belts do not prevent the tread from ballooning out.
b) That the full width of the footprint is in contact with the ground regardless of the load and inflation pressure.
This means that using the “chalk method” to determining the proper inflation pressure does NOT work 100% of the time.
****************************************************************
I’m stopping at 3 mistakes, but you get the idea.
It is unfortunate that many people have read this web page and have gathered up these mistakes as facts. Here’s one:
Originally Posted By: crosseyedwx
.....
The max pressure on the side of the tire simply represents the max load at that pressure, and that increasing your tires above that pressure does not increase the load carrying capacity of that tire. A tire at lower pressure does not have the same load capacity as a tire at higher. That is all that number means on the side of the tire, from my understanding, which I don't believe to be wrong. Is it perfect? Far from it.
………
Sorry, but the maximum pressure listed on the sidewall is not connected to the maximum load unless it specifically says so. I discuss this here:
http://www.geocities.com/barrystiretech/loadtables.html
About 1/3 of the way down the page, pay particular attention to “The notes on page 1-34”. There I discuss where the pressure on the sidewall comes from.
And just for the record: The pressure where the load maximizes is 35 psi for a standard load passenger car tire. (2.5 bar for SI based tire standardizing systems)
One of the things I don’t point out is that tire testing takes place based on the rated conditions – rated load / rated inflation pressure. That means that if you have a tire where the maximum pressure listed on the sidewall is 44 psi, that all the testing done on that tires was conducted based on the 35 psi as the rated condition (except of course, vehicle testing where the placard value is used.)
What I am trying to say is that if you are looking at the pressure listed on the sidewall as some sort of guide, be careful that you understand where it came from!
1) “The reason the owner’s manual lists 35 psi is because we get the same manual as the civilian version of the Crown Victoria.”
If Sgt. Storton had bothered to go down to the local Ford dealer, he would have realized this is not true – and the difference is enough to account for the extra stuff police vehicles carry (as he mentioned!)
2) "If you look on the sidewall of the tire, you will see that it lists 44 psi max pressure.”
If Sgt. Storton had bothered to look at other police pursuit tires, he would have realized that this is also not true. Some will list 51 psi as a maximum.
3) “ The tires will not balloon out creating a peak in the center portion of the tread when tire pressure is above 35 psi. There is a steel belt that prevents this from happening.”
This is something out of “The Pneumatic Tire” which is published by NHTSA. The book is over 700 pages long and is a compilation of articles written by tire industry experts. This particular chart is supposed to show the size of the footprint relaive to the load an inflation pressure – but it also shows a couple of other interesting things.
a) That lower the load / the higher the pressure, the more the footprint preesure in the center of the tread (and the lower the footprint pressure in the tread shoulders.)
So the belts do not prevent the tread from ballooning out.
b) That the full width of the footprint is in contact with the ground regardless of the load and inflation pressure.
This means that using the “chalk method” to determining the proper inflation pressure does NOT work 100% of the time.
****************************************************************
I’m stopping at 3 mistakes, but you get the idea.
It is unfortunate that many people have read this web page and have gathered up these mistakes as facts. Here’s one:
Originally Posted By: crosseyedwx
.....
The max pressure on the side of the tire simply represents the max load at that pressure, and that increasing your tires above that pressure does not increase the load carrying capacity of that tire. A tire at lower pressure does not have the same load capacity as a tire at higher. That is all that number means on the side of the tire, from my understanding, which I don't believe to be wrong. Is it perfect? Far from it.
………
Sorry, but the maximum pressure listed on the sidewall is not connected to the maximum load unless it specifically says so. I discuss this here:
http://www.geocities.com/barrystiretech/loadtables.html
About 1/3 of the way down the page, pay particular attention to “The notes on page 1-34”. There I discuss where the pressure on the sidewall comes from.
And just for the record: The pressure where the load maximizes is 35 psi for a standard load passenger car tire. (2.5 bar for SI based tire standardizing systems)
One of the things I don’t point out is that tire testing takes place based on the rated conditions – rated load / rated inflation pressure. That means that if you have a tire where the maximum pressure listed on the sidewall is 44 psi, that all the testing done on that tires was conducted based on the 35 psi as the rated condition (except of course, vehicle testing where the placard value is used.)
What I am trying to say is that if you are looking at the pressure listed on the sidewall as some sort of guide, be careful that you understand where it came from!
From what I gather, and thank you for that useful information, there is still no problem running your tires at 44psi. Now that I have more clarified information, I now better understand how loading standards are tested, but why then would they print 44 or 51psi if the tire itself is not safe at that pressure. Thank you for your civil clarification.
What I am saying is that I have driven my vehicles with tire pressures at placard and at higher pressures (printed max or slightly above), and every time, I felt I had better control of my vehicle with the higher pressures. Steering wasn't sloppy, cornering was crisper, and at 16000 miles on my current set of tires on my Kia, they literally have lost 1-2/32 of tread depth across the width of the tire (new is 11/32). Mind you, I am not an intense driver, and I know this is a sensitive subject. Thank you for your patience.
What I am saying is that I have driven my vehicles with tire pressures at placard and at higher pressures (printed max or slightly above), and every time, I felt I had better control of my vehicle with the higher pressures. Steering wasn't sloppy, cornering was crisper, and at 16000 miles on my current set of tires on my Kia, they literally have lost 1-2/32 of tread depth across the width of the tire (new is 11/32). Mind you, I am not an intense driver, and I know this is a sensitive subject. Thank you for your patience.
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Any comment regarding my question? (Does load capacity refer to weight or to mass?)
What's it do me good if a tire has a load capacity of 500kg (mass), but the actual weight (force) on the tire can reach 800kg?
What's it do me good if a tire has a load capacity of 500kg (mass), but the actual weight (force) on the tire can reach 800kg?
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
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Originally Posted By: crosseyedwx
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Originally Posted By: moribundman
Originally Posted By: crosseyedwx
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Answer: You have to look up the car manufacturer's specs - which are conveniently located on the placard, which starting in 2008 is on the driver's door or doorpost.
Originally Posted By: crosseyedwx
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Answer: You have to look up the car manufacturer's specs - which are conveniently located on the placard, which starting in 2008 is on the driver's door or doorpost.
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- Messages
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Originally Posted By: CapriRacer
Originally Posted By: moribundman
Originally Posted By: crosseyedwx
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Answer: You have to look up the car manufacturer's specs - which are conveniently located on the placard, which starting in 2008 is on the driver's door or doorpost.
I have never had an issue finding out the the required tire specs for any of my cars.
I hate asking for a third or fourth time the same question, so I'm moving on, presuming nobody knows if the load capacity figure is established based on weight or mass. Why did I keep asking until now? I was wondering how people picked tires with the proper load capacity. I KNOW that most people DO NOT PAY ANY ATTENTION to load capacity when choosing tires. But whatever...
Originally Posted By: moribundman
Originally Posted By: crosseyedwx
Mori, I am pretty sure it refers to actual weight. Sorry I did not mention that...
So how would one go about figuring out which tire load number is required by one's vehicle (without cheating by looking up what specs the car manufacturer requires)?
Answer: You have to look up the car manufacturer's specs - which are conveniently located on the placard, which starting in 2008 is on the driver's door or doorpost.
I have never had an issue finding out the the required tire specs for any of my cars.
I hate asking for a third or fourth time the same question, so I'm moving on, presuming nobody knows if the load capacity figure is established based on weight or mass. Why did I keep asking until now? I was wondering how people picked tires with the proper load capacity. I KNOW that most people DO NOT PAY ANY ATTENTION to load capacity when choosing tires. But whatever...
Originally Posted By: crosseyedwx
From what I gather, and thank you for that useful information, there is still no problem running your tires at 44psi. Now that I have more clarified information, I now better understand how loading standards are tested, but why then would they print 44 or 51psi if the tire itself is not safe at that pressure. Thank you for your civil clarification.
What I am saying is that I have driven my vehicles with tire pressures at placard and at higher pressures (printed max or slightly above), and every time, I felt I had better control of my vehicle with the higher pressures. Steering wasn't sloppy, cornering was crisper, and at 16000 miles on my current set of tires on my Kia, they literally have lost 1-2/32 of tread depth across the width of the tire (new is 11/32). Mind you, I am not an intense driver, and I know this is a sensitive subject. Thank you for your patience.
Let's put it like this: Everything is a compromise and there are a lot of compromises both in the design of a tire and the way it is used.
In the case of inflation pressure, obviously the ride quality goes down as the inflation pressure goes - and, of course, that leads to the question of the fatigue life of the rest of the vehicle components. Personally, I don't know a lot about other vehicle components, so I can't offer guidance in that area.
But tire impact resistance also goes down as inflation pressure goes up. You can subdivide "impacts" into 2 types:
1) Impacts where the sidewall of the tire folds over and touches together, and the cords in the sidewall are ruptured. Obviously more inflation pressure reduces the liklihood of this by increasing the spring rate of the tire- and obviously this type of impact is more prevalent in lower aspect ratios.
2) Impacts where an object deflects the tire in some other location and the sidewall is not squeezed together and the cords break. A longstanding tire test which simulates this is called a "Plunger Energy" test where a 3/4 diameter probe with a hemispherical end is slowly forced into the tire at the centerline of the tread. What is measured is the energy the tire absorbs before it is ruptured - the force generated times the distance traveled. Increasing the inflation pressure increases the spring rate, but because the cords of the tire are already in tension due to the inflation pressure, the probe merely adds to the tensions and the distance traveled not only is reduced for the same level of energy, but the tire ruptures at a reduced energy level.
While impacts of this type are fairly rare, the results can be quite dramatic, especially if you are traveling at high speed.
But the intent of allowing high pressures usage in passenger car tires was for high speed operation. That would involve smoother roads - which reduces the risk of an impact related failure. So I think this becomes a "wash", from a risk point of view.
In addition to the spring rate of the tire going up as the inflation pressure goes up, but the overall stiffness of the tire also goes up. This results in less wear and a faster response to steering input. Let me explore this for a moment.
Most of us aren't really aware of the time lag between our turning the steering wheel and when the tire reacts (and when the vehicle reacts). But if you do a back to back when the tire pressure is increased, almost everyone will feel the difference. However, many of us interpret this "quickness" as increased cornering power - and that would be wrong. But, certainly the vehicle feels more responsive - and that's a good thing up to a point.
I have been searching for what are called "carpet plots" of typical passenger car tires. Carpet plots are the output of a "Force and Moment" machine which inputs slip angle, camber, vertical load, and tire pressure and the output is side force.
In "the good old days", this was graphed out - and it was several graphs because of all the variables - but because this information is really of no value except when doing suspension studies, the data is now left in the form of a data table for computers to use when running vehicle simulations.
I mention this because I want to verify that increased inflation pressures results in a reduced slip angle for the same vertical load and side load - but more importantly, I want to see if the slip angle / side force is more linear at higher slip angles (I suspect it is) and that means that the vehicle will feel more predictable at higher cornering levels. (But you can also achieve this by increasing the tire's load capacity - which is what I think happened in the 1988 to 1995 time frame)
But does increased inflation pressure result in creased cornering force. When I was racing on street based tires, I thought so. But now I am not so sure.
I know that increased cornering levels benefit from reduced steering akerman (the difference between the turned angles of the front tires.) and coincidentally, this is one of the things that increased inflation pressure results in. But does this translate into actual improved grip or is it just that it is easier to control the vehicle, so the driver feels more confident and drives harder?
Lots of questions and not a whole lot of data.
But let me point out one thing:
When tires are designed, the amount of cord - both belt and casing - is carefully considered. But there is an engineering principal called fatigue. Here's a link to a Wikipedia article:
http://en.wikipedia.org/wiki/Fatigue_(material)
Please note the S-N Curve. These curves are similar for many engineering materials - including rubber.
If a tire travels 50,000 miles, it "cycles" somewhere in the vicinity of 60 million times - which is off the edge of the graph posted. But if you calculate the ratio of how much the stressed has to be reduced in order to survive 6 X10^7 cycles, you'll find it is on the order of about 5 - which means that a tire that is designed to survive 50 psi in service, should be designed to survive a 250 psi burst pressures.
If you read more of the article, you'll see that they refer to Minor's Rule, which says that under variable stress (which is what a tire experiences) the cycles to failure can be expressed as a function of the average stress. In the case of tires, we're talking about tire cords and they are prestressed by the inflation pressure - and then the "stress cycles" is applied on top of that! I don't think the stresses are reduced by using increased inflation pressure - just the opposite. And as proof I offer the aformentioned plunger energy test.
So I am urging caution until more data comes in. To give you an idea of "how much data" we need:
Deep within Dr. Govindjee's report on the Firestone tires is a statement that the actual failure rate of these tires was a fraction of a percent. This struck me, because I had come to pretty much that same conclusion based on what information I had availble to me.
Dr. Govindje was not more specific than that, so let's assume the actual failure rate was ½%. That's one failure out of 200 tires or one out of 50 vehicles. If the tires went 30K miles, then that is one failure out of 1½ million miles. So that would be a indication that things are very, very bad!
So what is the failure rate of a normal tire? Sorry, not only don't I know, and that answer has been constantly growing smaller, but it is also a company secret. But let's assume that the Firestone was a "tail of the curve" sort of thing and that at the time, normal tires were 50 times better (that's in Dr. Givindjee's report, too!).
That means the failure rate would be one out of 2500 vehicles or one out of 75 million miles! Needless to say, this is a huge number and one where the samples - the number of vehicles - has to be enormous to get meaningful results.
And I haven't even mentioned that data collection from an internet posting forum (like this one) is pretty dodgy and suspect!
Now, that's a lot of background information, but that's where I am coming from.
From what I gather, and thank you for that useful information, there is still no problem running your tires at 44psi. Now that I have more clarified information, I now better understand how loading standards are tested, but why then would they print 44 or 51psi if the tire itself is not safe at that pressure. Thank you for your civil clarification.
What I am saying is that I have driven my vehicles with tire pressures at placard and at higher pressures (printed max or slightly above), and every time, I felt I had better control of my vehicle with the higher pressures. Steering wasn't sloppy, cornering was crisper, and at 16000 miles on my current set of tires on my Kia, they literally have lost 1-2/32 of tread depth across the width of the tire (new is 11/32). Mind you, I am not an intense driver, and I know this is a sensitive subject. Thank you for your patience.
Let's put it like this: Everything is a compromise and there are a lot of compromises both in the design of a tire and the way it is used.
In the case of inflation pressure, obviously the ride quality goes down as the inflation pressure goes - and, of course, that leads to the question of the fatigue life of the rest of the vehicle components. Personally, I don't know a lot about other vehicle components, so I can't offer guidance in that area.
But tire impact resistance also goes down as inflation pressure goes up. You can subdivide "impacts" into 2 types:
1) Impacts where the sidewall of the tire folds over and touches together, and the cords in the sidewall are ruptured. Obviously more inflation pressure reduces the liklihood of this by increasing the spring rate of the tire- and obviously this type of impact is more prevalent in lower aspect ratios.
2) Impacts where an object deflects the tire in some other location and the sidewall is not squeezed together and the cords break. A longstanding tire test which simulates this is called a "Plunger Energy" test where a 3/4 diameter probe with a hemispherical end is slowly forced into the tire at the centerline of the tread. What is measured is the energy the tire absorbs before it is ruptured - the force generated times the distance traveled. Increasing the inflation pressure increases the spring rate, but because the cords of the tire are already in tension due to the inflation pressure, the probe merely adds to the tensions and the distance traveled not only is reduced for the same level of energy, but the tire ruptures at a reduced energy level.
While impacts of this type are fairly rare, the results can be quite dramatic, especially if you are traveling at high speed.
But the intent of allowing high pressures usage in passenger car tires was for high speed operation. That would involve smoother roads - which reduces the risk of an impact related failure. So I think this becomes a "wash", from a risk point of view.
In addition to the spring rate of the tire going up as the inflation pressure goes up, but the overall stiffness of the tire also goes up. This results in less wear and a faster response to steering input. Let me explore this for a moment.
Most of us aren't really aware of the time lag between our turning the steering wheel and when the tire reacts (and when the vehicle reacts). But if you do a back to back when the tire pressure is increased, almost everyone will feel the difference. However, many of us interpret this "quickness" as increased cornering power - and that would be wrong. But, certainly the vehicle feels more responsive - and that's a good thing up to a point.
I have been searching for what are called "carpet plots" of typical passenger car tires. Carpet plots are the output of a "Force and Moment" machine which inputs slip angle, camber, vertical load, and tire pressure and the output is side force.
In "the good old days", this was graphed out - and it was several graphs because of all the variables - but because this information is really of no value except when doing suspension studies, the data is now left in the form of a data table for computers to use when running vehicle simulations.
I mention this because I want to verify that increased inflation pressures results in a reduced slip angle for the same vertical load and side load - but more importantly, I want to see if the slip angle / side force is more linear at higher slip angles (I suspect it is) and that means that the vehicle will feel more predictable at higher cornering levels. (But you can also achieve this by increasing the tire's load capacity - which is what I think happened in the 1988 to 1995 time frame)
But does increased inflation pressure result in creased cornering force. When I was racing on street based tires, I thought so. But now I am not so sure.
I know that increased cornering levels benefit from reduced steering akerman (the difference between the turned angles of the front tires.) and coincidentally, this is one of the things that increased inflation pressure results in. But does this translate into actual improved grip or is it just that it is easier to control the vehicle, so the driver feels more confident and drives harder?
Lots of questions and not a whole lot of data.
But let me point out one thing:
When tires are designed, the amount of cord - both belt and casing - is carefully considered. But there is an engineering principal called fatigue. Here's a link to a Wikipedia article:
http://en.wikipedia.org/wiki/Fatigue_(material)
Please note the S-N Curve. These curves are similar for many engineering materials - including rubber.
If a tire travels 50,000 miles, it "cycles" somewhere in the vicinity of 60 million times - which is off the edge of the graph posted. But if you calculate the ratio of how much the stressed has to be reduced in order to survive 6 X10^7 cycles, you'll find it is on the order of about 5 - which means that a tire that is designed to survive 50 psi in service, should be designed to survive a 250 psi burst pressures.
If you read more of the article, you'll see that they refer to Minor's Rule, which says that under variable stress (which is what a tire experiences) the cycles to failure can be expressed as a function of the average stress. In the case of tires, we're talking about tire cords and they are prestressed by the inflation pressure - and then the "stress cycles" is applied on top of that! I don't think the stresses are reduced by using increased inflation pressure - just the opposite. And as proof I offer the aformentioned plunger energy test.
So I am urging caution until more data comes in. To give you an idea of "how much data" we need:
Deep within Dr. Govindjee's report on the Firestone tires is a statement that the actual failure rate of these tires was a fraction of a percent. This struck me, because I had come to pretty much that same conclusion based on what information I had availble to me.
Dr. Govindje was not more specific than that, so let's assume the actual failure rate was ½%. That's one failure out of 200 tires or one out of 50 vehicles. If the tires went 30K miles, then that is one failure out of 1½ million miles. So that would be a indication that things are very, very bad!
So what is the failure rate of a normal tire? Sorry, not only don't I know, and that answer has been constantly growing smaller, but it is also a company secret. But let's assume that the Firestone was a "tail of the curve" sort of thing and that at the time, normal tires were 50 times better (that's in Dr. Givindjee's report, too!).
That means the failure rate would be one out of 2500 vehicles or one out of 75 million miles! Needless to say, this is a huge number and one where the samples - the number of vehicles - has to be enormous to get meaningful results.
And I haven't even mentioned that data collection from an internet posting forum (like this one) is pretty dodgy and suspect!
Now, that's a lot of background information, but that's where I am coming from.
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