tire pressure myth?

[2.2 Straight six]

Originally Posted by UncleBob

you seem to be rather insistant that you understand this better than everyone, when a awful lot of people say otherwise.

If you'd like some credentials....I work at a tire store. We're not making this stuff up.

you can't argue with that.

if you want more proof that tyre running pressure is decided by vehicle weight and is decided by the vehicle manufacturer i suggest you look at some large trucks like semis, dump trucks etc..

i've seen a lot of them here with the tyre pressure labeled on each individual wheelarch. this is decided by the manufacturer, not the operator, not the driver, not the tyre company, not even that guy with the moustache that lives 5 doors down.

maybe you shouldn't argue with the experts here, Curtis, Moppie, UncleBob and some others are the experts here. they know more about cars that you could imagine, so don't argue.

you're outnumbered in opinion when it comes to what that number represents anyway.

[KiwiBacon]

44psi is dangerous for a light car.
Your contact patch is severely reduced, which reduces grip.

Here's how I set my tyre pressure:
Drive at your normal open road cruising speed, pull over and feel the temperature of the tyre.

Warmer on the sides means the pressure is too low.
Warmer in the middle means the pressure is too high.

Get it right and you'll get even tyre wear and even temperature distribution.

For reference this gives me 40psi running 600kg on each 225/85R16 LT tyre.

[JustSayGo]

In the name of Democracy! The guys in white sheets made sure they always outnumbered their victims and began their meetings reading from the Bible. They believed they were right and that their work was what God and the majority wanted done.

Seems to me 2.2 may be trying to pull his experts under his sheet.

There are small car tires that are safe and recomended inflated to 44lbs

Tires are constructed in ways that maximum tire presure is determined by a calculated formula which is based on their individual design.

Tires are capable of supporting the greatest load at their maximum inflation pressure.

Tires are designed to provide the greatest wear and fuel milage at the maximum inflation pressure.

Tires are designed to provide even wear over a range of pressure and varios load.

Tires are run lower than max inflation to improve ride comfort.

Due to construction, Tires can and have worn more on the outside edges because of over or max inflation. Bands in tires can be designed and constructed in ways that prevent the center of the tread from expanding as much as the edges when the tire is inflated. Tires are a very sophisticated balloon.

Some of the most significant evidence presented against the Ford Motor Company in their Explorer roll over because of tire failure law suite (which they lost seriosly big $$$), delt with stickers on the door that were lower pressure than the tire manufacture had recomrnded.

Tire expence is the second greatest operating expence, fuel being the first. Tire manufacture factory reps do tire tests together with fleet vehicle owners to determine the best tire pressure decal to place on the body at each wheel for that fleet. The pressures on the stickers are updated and adjusted periodicly as conditions change and newer tests dictate need. The tire pressure is ultamatly decided by the fleet owner. I have been part of the testing, inflating, and putting the sticers on, for the largest fleet in the world and another extreemly well recognized large fleet. I have had extensive training and conversation with the major tire reps. Each rep is preaching the same info.

Competition between tire manufactures supplying fleets is fierce. They send their best reps to fleets to measure and optimize expence. Tire sales reps who visit tire stores advise on how to sell the most tires by giving the public what they want most.

Fleets pay their techs to maintain tire pressure so often that the pressure is maintained well within 5% of their determined inflation pressure.

Maintaining tire pressure is critical. When ever I did side jobs, regardless of replacing brakes, clutch, or tune-up, I always aired the tires to the max inflation, partly because of my fleet background and because often I found the tires had deflated to only 18-20lbs when max was 32-36lbs. Little wonder that some told me, "you know, my car always drives better after you have worked on it." "I don't understand how this type of repair can make my car feel different and drive better?"

Even after inflating so many tires for too many years, I am somewhat amazed at my own newest tires that are nitrogen filled to 28lbs (max may be 36lbs) after more than a year they still gave 28lbs. Heat does not change pressure of nitrogen filled tires.

Manufactures recomend very close to the max and never stop talking about maintaning pressure.

In the case of your girlfriend, I recomend giving her what She wants!

[Alastor187]

Originally Posted by JustSayGo

...Heat does not change pressure of nitrogen filled tires...

Isothermal tires?

[KiwiBacon]

Originally Posted by JustSayGo

In the name of Democracy! The guys in white sheets made sure they always outnumbered their victims and began their meetings reading from the Bible. They believed they were right and that their work was what God and the majority wanted done.

Seems to me 2.2 may be trying to pull his experts under his sheet.

There are small car tires that are safe and recomended inflated to 44lbs

Tires are constructed in ways that maximum tire presure is determined by a calculated formula which is based on their individual design.

Tires are capable of supporting the greatest load at their maximum inflation pressure.

Tires are designed to provide the greatest wear and fuel milage at the maximum inflation pressure.

Tires are designed to provide even wear over a range of pressure and varios load.

Tires are run lower than max inflation to improve ride comfort.

Which part of "contact patch" do you not understand?

The higher the tyre pressure, the smaller the contact patch, the less grip you have.

44psi in a passenger car is dangerously high, your contact patch is approximately 50% smaller than it should be and your grip is seriously compromised.

In addition you will wear out the centre of the tyre tread, causing replacement to be required much sooner and increasing the owners running costs.

Maximum inflation pressure is only for use at the maximum weight the tyre can carry.

[UncleBob]

Originally Posted by JustSayGo

There are small car tires that are safe and recomended inflated to 44lbs

correction, there are small car tires that have a WEIGHT RATING that can acheive 44 psi. Simular, but not the same

Tires are constructed in ways that maximum tire presure is determined by a calculated formula which is based on their individual design.

bullshit. To put it nicely.

I assume you're talking about runflat tires? If you think they are incapable of overinflation damage because they have such stiff sidewalls, you'd be quite wrong.

As kiwi pointed out, weight/psi = contact patch. No matter how stiff the side walls are. Really.

Tires are capable of supporting the greatest load at their maximum inflation pressure.

100% agree. Thats the entire purpose of the listed maximum weight the tire can support....which is also listed with the maximum psi. They go hand in hand.

Tires are designed to provide the greatest wear and fuel milage at the maximum inflation pressure.

Wrong. Tires are designed to have the greatest wear mileage at the proper inflation for the vehicle weight.

Best mileage would be at maximum inflation the tire could support, but would cause the tires to wear accessively

Tires are designed to provide even wear over a range of pressure and varios load.

only if the vehicle weight corresponded with the tire psi.

Its been stated over and over. psi = weight capacity. Its a very simple formula

Tires are run lower than max inflation to improve ride comfort.

this is definitely true.

Due to construction, Tires can and have worn more on the outside edges because of over or max inflation. Bands in tires can be designed and constructed in ways that prevent the center of the tread from expanding as much as the edges when the tire is inflated. Tires are a very sophisticated balloon.

Let turn the tables here on this belief. If a tire is so stiff that it will keep an even form across the contact patch regardless of psi....

why does it need any psi?

comprenda?

Some of the most significant evidence presented against the Ford Motor Company in their Explorer roll over because of tire failure law suite (which they lost seriosly big $$$), delt with stickers on the door that were lower pressure than the tire manufacture had recomrnded.

correct. That was firestones argument. Ford set the psi in the door jam lower than was realistic for the vehicle weight, for two reasons. One was ride quality. The second might surprise you, it was to prevent roll overs. The CG was a contention with the engineers, so this was one tiny aspect that they manipulated to lower it to help prevent roll overs. Funny eh?

The part that I find amusing about such arguements about the firestone/ford thing, is that 99.9% of car owners don't even know about the sticker in their door jam, so its really quite mute on whats printed on it. Most people wait til their tires are so flat its riding on the rim before they do anything about it. Thats my experience anyway.

Manufactures recomend very close to the max.

uh. No they don't. Most manufacturers don't put that crappy a tire on their cars.

[UncleBob]

here's a mind bender for car people.

What is the proper inflation psi based off of......on a bike tire?

It has a round profile, which is desired to support lean angles. The contact patch will obviously get bigger the less psi you have, but there is some major issues with a under-inflated tire on a motorcycle. Stability becomes very bad at some point.

Its a little mind teaser for those that have never dealt with bike tire inflation. Do the same rules apply, as I've listed above, for cars? Is weight the ultimate consideration, even though it won't ultimately cause an "even" contact patch across the tire? What ARE the factors involved here?

[Moppie]

Originally Posted by JustSayGo

In the name of Democracy! The guys in white sheets made sure they always outnumbered their victims and began their meetings reading from the Bible. They believed they were right and that their work was what God and the majority wanted done.

Seems to me 2.2 may be trying to pull his experts under his sheet.

Riiight, except your the one giveing some very irrational reasoning, and backing it up with rethoric.
Prehaps we should all join you in your sheet?
Oh! Thats right, we have knowledge, experiance and rational thought on our side.


Iv added some comments in red:

Originally Posted by JustSayGo

There are small car tires that are safe and recomended inflated to 44lbs

Yip, thier called space saver spare tyres. They run a very high side wall, and a very small contact patch. They also have a very limited life.

Tires are constructed in ways that maximum tire presure is determined by a calculated formula which is based on their individual design.

I would hope some engineering and calculating went to it

Tires are capable of supporting the greatest load at their maximum inflation pressure.

As has already been stated. Max load needs max pressure, right again.

Tires are designed to provide the greatest wear and fuel milage at the maximum inflation pressure.

Yip, true again, high pressure equals small contact patch, equals lower roller resistance, equals better fuel milage. It also means the tyre will wear faster since not all of its contact patch is being used, the small part that is wears more, and un-evenly across the face of the tyre. You can also get problems from the tyre over heating. And of course its very dangerous, since the car has less traction that it was designed to have.

Tires are designed to provide even wear over a range of pressure and varios load.

Of course, assuming the pressure matchs the load.

Tires are run lower than max inflation to improve ride comfort.

Yip, common problem with used Jap imports sold here in NZ and else where in the world. The recomended prssure is one for driving around Japan, and for a market that generaly values comfort over performance. They also have radicaly different speed limits, to the rest of the world, with most cars never getting above 60kph in thier life. So, they have lower tyre pressures recomended by the manufactors. They also carry less weight in thier cars, as the population generaly weights less. The exact same car, sold here in NZ, where the speed limits are much higher, and its very easy to drive long distances at 100kph, and as a population we weigh more, and carry more, comes with a manufactors put a tyre pressure recomendation that can be 4-6psi higher.
Basicly what works in Japan, becomes dangerously under inflated here in NZ.
Some local manufactors that took to importing and renewing and then selling thier own brand of car from Japan even goto the trouble of replacing the Japanese tyre prssure recomendation plate.


Due to construction, Tires can and have worn more on the outside edges because of over or max inflation. Bands in tires can be designed and constructed in ways that prevent the center of the tread from expanding as much as the edges when the tire is inflated. Tires are a very sophisticated balloon.

Yip, another good reason not to over inflate your tyres, and why a pressure guage is very important to keep in your car if your serious about getting the pressure right. Nothing worse than uneven wear on a tyre.


Some of the most significant evidence presented against the Ford Motor Company in their Explorer roll over because of tire failure law suite (which they lost seriosly big $$$), delt with stickers on the door that were lower pressure than the tire manufacture had recomrnded.

Not relevant to the thread, but ok.

Tire expence is the second greatest operating expence, fuel being the first. Tire manufacture factory reps do tire tests together with fleet vehicle owners to determine the best tire pressure decal to place on the body at each wheel for that fleet. The pressures on the stickers are updated and adjusted periodicly as conditions change and newer tests dictate need. The tire pressure is ultamatly decided by the fleet owner. I have been part of the testing, inflating, and putting the sticers on, for the largest fleet in the world and another extreemly well recognized large fleet. I have had extensive training and conversation with the major tire reps. Each rep is preaching the same info.

And just what is this info? Im very familar with fleet work, I help look after a small fleet of trucks. Im also well aware that the pressure recomended by the manufactor is not always right, for all situation. There is often a trade off in tyre life, vs performance, or comfort. As a general rule on every car Iv owned I taken the manufactors recomendation, and added about 4psi, then adjusted it to suit, based on driving feel, tyre temps (measured) and wear across the contact patch. At the moment I run 32 on the front of my car, where 28 is recomended.

Competition between tire manufactures supplying fleets is fierce. They send their best reps to fleets to measure and optimize expence. Tire sales reps who visit tire stores advise on how to sell the most tires by giving the public what they want most.

Fleets pay their techs to maintain tire pressure so often that the pressure is maintained well within 5% of their determined inflation pressure.

Sounds like good business practice, but has nothing to do with this thread

Originally Posted by JustSayGo

Maintaining tire pressure is critical. When ever I did side jobs, regardless of replacing brakes, clutch, or tune-up, I always aired the tires to the max inflation, partly because of my fleet background and because often I found the tires had deflated to only 18-20lbs when max was 32-36lbs. Little wonder that some told me, "you know, my car always drives better after you have worked on it." "I don't understand how this type of repair can make my car feel different and drive better?"

On a large car, or one with low profile tryes then 32-36psi is about right. Infact some very, very low profile tyres (50% and below) recomended pressure can be 42psi or more, or the very low side wall is unable to surport the weight of the vechile, and maintian its shape in corners.
But 32-36psi is certianly not max pressure. Unless your talking about the manufacotors recomended max, pressure, and not the max pressure printed on the tyres side wall, which is what the thread started is refering to.

Originally Posted by JustSayGo

Even after inflating so many tires for too many years, I am somewhat amazed at my own newest tires that are nitrogen filled to 28lbs (max may be 36lbs) after more than a year they still gave 28lbs. Heat does not change pressure of nitrogen filled tires.

Being an inert gas Nitrogen dosn't experiance the same changes in volume with changes in temprature that breathable air does because of its Oxygen content. There are better gases to use, Ill be damned if I can remember what they are though.

Originally Posted by JustSayGo

Manufactures recomend very close to the max and never stop talking about maintaning pressure.

Tyre manufactors or car manufactors?
Because they both recomend a different max pressure, for the tyre manufactor its the point at which the tyre can't hold any more weight, and adding more becomes dangerous.
For the car manufactors its the point at the which the car, when fully loaded will be surported by a tyre with a complete contact patch, and provide the car manufactors idea of the ideal ride and performance.
There is nothing terriably wrong with following the car manufactors recomended max, although if have very little weight in your car you may be compromising total tyre grip by slightly reduceing its contact patch.
If you follow the tyre manufactors recomended max your are an idiot unless its matchs the cars max, and you are also carrying the cars maximum pay load.
But since the tyres recomended max is usualy 20-30% more than the max of the car its fitted to, all you end up doing is reducing the tyres contact patch to a very dangerous level.

Originally Posted by JustSayGo

In the case of your girlfriend, I recomend giving her what She wants!

Congratulations, you have a just given a recomdation that will lead to a dangerous situation for his girlfriend, and anyone else who has to share the road with her.
And is all based on reasoning that draws a very different conclusion.

[Moppie]

Originally Posted by UncleBob

Its a little mind teaser for those that have never dealt with bike tire inflation. Do the same rules apply, as I've listed above, for cars? Is weight the ultimate consideration, even though it won't ultimately cause an "even" contact patch across the tire? What ARE the factors involved here?

A little help:

Remember that weight is a factor of force AND mass
In mid corner a bike can generate some very high forces, and tyre pressures need to reflect that.

[UncleBob]

Originally Posted by Moppie

A little help:

Remember that weight is a factor of force AND mass
In mid corner a bike can generate some very high forces, and tyre pressures need to reflect that.

oooh....I like the way you think!

you are correct that weight involves force and mass....but here's the kicker. A higher force in the corners would cause the contact patch to get bigger.

Thats a good thing....up to a point

[Moppie]

Originally Posted by UncleBob

oooh....I like the way you think!

I spent a long time riding a push bike as a kid, and plenty of time playing with tyre pressures while doing so

Air serves two purposes in a tyre.
It holds the weight of the vechile the tyre is attached to, AND it helps the tyre hold its shape.
And of course the shape a tyre has dictates its contact patch on the road surface, which of course dictates how much grip it will have.
Different tyres, used in different aplications, rely on different shapes, which require different air pressures in oder to hold up under the forces exerted on them by a vehcile.


With relation to bike tyre pressures vs car tyre pressures, think about the different jobs they do, and how they have to do it.
And, an extra little hint, very low profile tyres on a car have to behave in a similar manner as tyres on a bike with a large side wall contact patch (although that might confuse some people).

[534BC]

I don't know much abouit bike tires other than what I can see that they are large, round, round and someone once told me that when spinning they want to "stand up" gyro or something.

I once picked up a load with an old backhoe with car tires on the front end (aired to 100 pounds) and the rim beads were touching the insides of the treads, lol.

We measured it and laughed. Does that count for anything?

[UncleBob]

bike tires follow many of the same principles as car tires.

Weight is still a key factor, but it has more to do with tire performance.

Since there is no tire shape that you are trying to maintain, maxing out the tire pressure on any bike will increase your mileage because it reduces the contact patch, with no side effects to the tire. It in fact, increases tire life. Less contact patch means less heat for the tire.

The side effect, of course, is traction. Less contact patch will of course reduce traction, but the heat is an important factor also. Bike tires are much stickier than car tires, but they require a certain amount of heat to work optimally.

So for high performance riding, you drop the tire pressures to increase traction. The tire will wear faster because of this. The range you have availible to play with is quite large, say 20psi to 42psi.

The handling disadvantage with low pressure is it takes more steering effort to get a bike leaned over. The larger contact patch makes it resists the angle changes more. This doesn't prevent a bike from handling well, but many riders dislike the added steering effort.

I run my rear tire at 20-30psi, depending on what I'm doing. This is quite low compared to most. The reason being, the turbo makes rear wheel traction a challenge. But just by dropping my tire pressure, it will take every bit of HP I can throw at it. Quite impressive when you put it in car terms, of power to weight ratio....no car could keep traction with that level of P/W, without using special tires and chasis tuning.
__________________

[GreyGoose006]

Originally Posted by JustSayGo

Let them fill their tires as they see fit.Those guys sound like they are clutching at their chest with both hands and sticking one leg outta bed. They have a fairly clear understanding of 1975 tire technology and refuse to ackowledge the improvements that TIRE manufactures are continuosly making every day.

I pretty sure that none of the major TIRE manufactures will be consulting these guys asking for their recomendations on tire inflation any time soon.

Thirty years ago American cars weighed 4-6,000lbs and all tires said 28-32 lbs max inflation on the sidewall. Todays cars weigh around 3,000 lbs and in many cases have much wider tires than the typical 70's auto. There has been a trend of gradually increasing tire inflation recomendations by TIRE manufactures over the past 30 years. Now we have tires that say 44lbs max PSI on them on realetivly light weight vehicles. Tire pressures are cold and should not be adjusted as heat increases tire pressure.

Modern automobile tires are far more sophisticated than comparing them to an illustrative example of a party balloon having limited structure. Modern technology of tire construction continues to reduce irregular tire wear problems that over years past were blamed totally on tire inflation. Engineers who design tires are blending construction and inflation together to develope and produce longer lasting, safer, and more fuel efficient tires. Before a tire design ever leaves the computer drawing board, the engineers know what the tire should do at the tire pressure it has been designed to work at.

If your tires are the size recommended by the AUTO manufacture, the max tire pressure molded into the side wall by the TIRE manufacture will not create a liability to them or cause the tire to dervolope undisirable characteristics, contact patch, or otherwise reduce safety.

this was posted in the caprice forum when i mentioned the hot debate going on over here.

i'm sorry, but if the sidewall of my tire says 44psi. (it does), i'm gonna inflate it to 44psi. if it says 15, i'll happily put 15psi. in it.

as soon as you change from the tires that came on the car, you can ignore the doorjamb's sugestion.

my car is an '84 caprice classic.
it CAME w/ 205 wide tires that inflated to 25psi.

police 9c1 caprices came w/ 225 wide tires. i'm guessing they were at 25psi.

i put new 235 wide 44psi. tire on.
i inflate them to 44 psi.

if i inflated 44psi. tires to 25psi., all i'd be doing is decreasing my gas mileage, and causing accelerated tire wear and premature tire failure.

at $85 ea.
i'll inflate to 44psi thank you.

[Moppie]

Originally Posted by GreyGoose006

i'm sorry, but if the sidewall of my tire says 44psi. (it does), i'm gonna inflate it to 44psi. if it says 15, i'll happily put 15psi. in it.

as soon as you change from the tires that came on the car, you can ignore the doorjamb's sugestion.

my car is an '84 caprice classic.
it CAME w/ 205 wide tires that inflated to 25psi.

police 9c1 caprices came w/ 225 wide tires. i'm guessing they were at 25psi.

i put new 235 wide 44psi. tire on.
i inflate them to 44 psi.

if i inflated 44psi. tires to 25psi., all i'd be doing is decreasing my gas mileage, and causing accelerated tire wear and premature tire failure.

at $85 ea.
i'll inflate to 44psi thank you.

Wow.

Have you read anything in this thread?
Or you just out to kill yourself in you car?