Tire Pressure

I apologize for the crosspost...
I have a pair of Neons, an '03 and an '04, and the tire pressure was getting low in the '03. I've never checked it since we've had it, but it was reading
about 27 psi at each wheel. The door sticker reads 32 psi but the tire sidewall reads a max of 44 psi. So I'm wondering what should the pressure be set at? In years past, I always went about 4-6 psi less than the max listed on the tire to account for temperature changes, altitude, etc. So I ended up going with 38 psi all around. The ride is much firmer and I'm wondering if it's meant to be at 32 psi after all.
Any suggestions?
Thanks, NG
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NG wrote:

I could be wrong about this, but my view has always been that automotive manufacturers are paid to engineer these things to a specification exacting enough to provide the best longevity at the least cost with the tools and technologies they are given (permitted?) to use. With this in mind, they're not going to cheap out on tire research when that's a very extremely important aspect of the overall vehicle. They're going to do the research, do the stress testing, do the road testing, and they're eventually going to get to the right tire pressure that permits for things like road temperature, vehicle weights, etc., and therefore all you need to do is fill the tires to the point they tell you to. MY far-from-expert advice would be not to second-guess an engineer who probably earns a hell of a lot more than any of us do, and to trust what they tell you is appropriate for your vehicle.
OTOH, if you're an automotive professional with years of training and very expensive education in the matter, you could probably customize every little nuance of your ride to fit your driving style, but what they came up with is pretty much guaranteed to work for all sane driving styles.
FWIW, I fill mine to 32 psi. Mine hold air with no problem. About every 6 months or so I have to put just a couple psi in, but not much. If you haven't lost but 5 psi over a year and a half, that's not bad at all. Just put it back at 32 and keep a regular check on it.
As for altitude, even at sea level we're only under 14 psi or so, so I'd imagine at 50,000 feet it would only drop 7 psi. We can't even get above 10,000 without the need for oxygen, and not much higher before we need pressurization, but I don't see altitude really affecting automotive tires to the point you need to concern yourself with it.
Which also makes me wonder if you even need to worry about road conditions: do a simple test... take the psi reading before you go driving, and then take the family on a nice scenic drive or something (good 30 minutes or so at highway speed should do the trick) and when you get back home, check the pressure again while the tires are still warm. I doubt you'd see more than 4 or 5 psi difference, although it's a guess.
Again, I'm no expert. HIH.
CJ
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Circuit Breaker wrote:

If you're a tire, you don't really care what car you're on. You care if you're mounted on the correct-sized rim, and then you care about how many pounds you're being asked to carry.
It's actually a pretty dumb thing for car makers to put the tire PSI on the door jamb. Ok, well, they do know what tires they put on the car from the factory, so that's really the only *correct* situation where the door-jamb PSI spec is valid. Other than that, once you start putting on different tires (and different sizes) then the tire makers should have specs as to what a given tire should be pressurized to for a given weight to obtain the correct rolling profile.
You need enough pressure so that the tire doesn't deform a lot (flatten-out) as it turns. That's a function of the weight of the car (and all cars are different). Too much air results in too little contact patch surface (and a hard ride, and too much center wear, but probably great fuel economy).
Most passenger car tires know they're going to be carrying (3700 / 4 ) 925 lbs, so you'd think that instead of the ridiculous "max pressure" rating on a tire that there'd be *the correct freeking PSI rating* for 1000 lbs load.
What ever happened between Ford and Firestone's SUV tires? Was it proven that Ford's door-jamb rating was not correct for the particular tires that were blowing out on the highway?
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Having been in the tire business for over thirty years and have seen everything from the firestone 500 problem of the sixties to the present problems. The air pressure issue is very important. You should check your pressure based on the car makers recommendations. The pressure should be checked once a month after the car has set for over 8 hours. The proper way to do this as follows. check the recommended air pressure from the door jam, for this example lets use 32 psi. Measure the air pressure with a reliable gauge. Write down the pressure for each wheel position. i.e.; L/F 26 psi, R/F 29 psi etc. Then if you do not have your own compressor drive to the nearest service station that does and measure the pressure. IE the L/F now reads 29 psi and increase of 3 psi Inflate that tire to 35 psi ( 32 plus the 3 psi from the difference of being cold.) Then the following morning re-check
The problem with Ford and Firestone was 2 fold. Ford had recommended a low air pressure of 25 psi which would have been no problem if the average consumer checked his air pressure regularly. (not) The failure mainly occurred in high temperature areas where tires heat up faster.Also the fact that other tires had failed on the ford products leads one to believe that it was a design flaw on Ford's part. If you look at the location of the rear exhaust in relation to the rear tire it appears to be very close thereby adding extra heat .

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I couldn't believe my eyes when I saw Harold Seldin wrote:

25 PSI?!?! That tire is rated for something like 40-44 PSI! It would seem to me that this would result in *serious* overheating, even at Ford's recommended tire pressure!
FWIW, I generally go by the tire's sidewall, and go to the max. Usually I have a decent ride and decent gas mileage.

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This can lead to excessive wear in the center of the tire. --------- Alex
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HachiRoku wrote:

Why?
Yes, I think Ford really messed up if that was their recommended pressure for a vehicle the size of the Explorer.

I tend toward the max also, but keep in mind that this is really indicated if you have the tire loaded to the max load specified along with the max pressure. A lower pressure for a lower load isn't a bad thing.
Matt
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Circuit Breaker wrote:

Pretty bold assumptions there. Like everything, the recommended pressure is a compromise of many things. The ideal pressure for gas mileage will not be the ideal pressure for tread longevity will not be the ideal pressure for handling, will not be the ideal pressure for ride smoothness, etc., etc. A given manufacturer may put higher priority on soft ride (claimed by some to be an over-compromise that created or contributed to the more recent Firestone debacle), while the same manufacturer may put higher priority on handling on a different vehicle or even on a different version of the same vehicle (with, say, a handling package option). *Everything* is a compromise. The final answer depends on the weighting factors put on the various aspects of vehicle/tire ownership. Nothing wrong with an owner putting a higher priority on handling and tire longevity/even tread wear and cooler running temperatures and putting 2 to 4 psi higher than the recommended pressure. Going lower than that recommended rarely makes much sense.
Bill Putney (to reply by e-mail, replace the last letter of the alphabet in my address with "x")
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On Mon, 26 Jul 2004 20:49:52 +0000, NG wrote:

Of course it's meant to be at 32. Why do you think they put that sticker on the door?
Did you ever think to check the owner's manual for information?
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I've regarded the owner's manual recommendations as a starting point only, ever since the 1960s when tire pressures of 24 psi or so were recommended by ride-conscious automakers, much to the detriment of handling.
A point of warning: if you go by the door sticker alone, you may not be adhering to manufacturer's recommendations in "high speed" driving, which turns out to be what a lot of us actually do. Read your owner's manual. Note the example which follows.
I offset front vs. rear tire pressures to assist in adjusting the handling of my cars. My 1995 Dodge Intrepid departs from stock only in the replacement of one rear sway bar bushing on each side with polyurethane instead of the factory rubber parts; and revised tire sizing, replacing the factory's P205/70R15 with P215/65R15. The door sticker with tire pressures says 32 lbs., front and rear; HOWEVER the owner's manual says for sustained speeds of 75mph or more (and these days on expressways, 75mph is pretty much normal speed) the pressures should be increased to 35 lbs., front and rear. I run 39 lbs. on the front and 35 lbs. on the rear; this reduces understeer by increasing front tire grip, and with the "quicker" action of the rear sway bar due to the harder polyurethane bushing, it makes it easier, actually fun, to "toss" this relatively large vehicle into corners.
Near my home is a right/left S-bend, the left being sharper than the right, the whole having a mild dip at its entry. Box-stock, the car had a response which was safe but felt slow and sluggish here, especially at the transition in the middle of the S-bend where the front tires would plow. With the higher front tire pressure and the replacement bushings, response is quick and adhesion much better balanced between front and rear. In the middle of the S-bend, a quick turn of the wheel to the left is all it takes to bring the car around and exit straight out, while opening throttle and accelerating out. What's more, the whole, stable demeanor of the tires and chassis are such that I could do that kind of thing all day. And the tires wear flat across the tread grooves, too, even on the front.
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About 7 months ago I had new tires put on my wifes '00 Taurus at Firestone.
The tires started balding about 2 months ago, so I took it in.
They wouldn't warranty the tires because I inflated them to what it said on the sidewall of the tire. They told me to go by the vehicle manufacturers specifications no matter what, or the warranty is void.
Now, I'm not sure if they were just scamming me or what, but I've since gone by the factory manual and they haven't given me a problem since.

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wrote:

The sidewall pressure is the MAXIMUM allowabel pressure, which would be recommmended if operating the tire at MAXIMUM load. Any higher pressure and/or load and the tire is in danger of rupture. The car manufacturer /engineers decide what the proper tire pressure is for a given tire size when installed on the vehicle to give best combination of ride, handling, and tire-wear. Deviating from that pressure without a very good understanding of the loads and conditions involved is foolishness. If you understand the ramifications, small changes can safely be made.

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SMoo wrote:

Did they wear only in the center of the tread?

That's a pretty pathetic excuse. However, there must be more too it because even being overinflated by that amount wouldn't wear a tire to the point of being bald in only 5 months ... unless you drive 10,000 miles per month.

Is that clause in their written warranty? If not, then they need to honor their warranty.

The car maker's recommendations are typically a decent compromise, but they are a compromise. If you run your vehicle heavily loaded all of the time, then you likely need higher pressure. If you drive alone all of the time, the the manufacturer's recommendations are probably fine. I tend towards the max on the tire, especially on my pickup, and have have good tire life with only a slightly harsher ride.
Matt
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I agree.
On my LeBaron, I keep them inflated to what the sidewall says to inflate them to.
The reason being is that the Chrysler shop manual (Which wasn't cheap) says that any speed under 65mph to inflate them to 35 psi. Anything over 65mph, to go by the tire.
Soooooo, if I have to take it back to Firestone, I'll show them this in the shop manual, and wait for their next piece of shit excuse...

Firestone.
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SMoo wrote:

I've never seen a sidewall that has the "recommended" pressure stamped on it.
They usually have the "max pressure".
Tire makers seem reluctant to stamp a recommended pressure on tires. That seems odd. I'm sure they have a chart for every tire showing PSI on the Y axis and load (weight) on the X axis.
The max load rating of a tire is proportional to the volume of air contained within the tire. The wider and taller a tire is, the higher the MAX PSI is (and the higher the MAX load is).
http://www.goodyear.com/truck/pdf/databook/5113_Lsec_V.pdf http://www.tirerack.com/tires/tiretech/tirespecskey.jsp#maxload http://www.dodge.com/bodybuilder/2004/docs/intro/tirecharts.pdf
RV forums sometimes have tire PSI discussions - such as in this link:
http://www.rv.net/forums/index.cfm/fuseaction/thread/CFB/1/TID/246059.cfm
The correct strategy here is to "(1) weigh the rig and (2) consult the tire manufacturers load/ pressure charts to find the right (air pressure) value."
The PSI spec found on the door jam sticker of passenger cars assume that all tires have the same load/pressure chart (you tell me if that's a realistic assumption). It would be interesting to look at the tire inflation specs from 3 different 300M cars (one with 16" tires from the PHP package, one with the standard 17" wheels, and the third with 18" wheels from the 300M Special package). Are the PSI values different?
Clearly, the PSI value on the door sticker has some over-all car weight in mind. If it's the GVWR (max gross weight which is a fully loaded car) then if you drive around with only yourself (and not 4 other adult passengers) then inflating your tires to the spec value is technically over-inflation for what you're doing (it's safe, and it's probably going to give you good milage, but it's going to give you a harsh ride - and depending on the conditions of your roads your tire will experience more internal "injury" with higher PSI's).

The goodyear link (above) has a chart which also indicates that up to 5 extra PSI (for car tires) and 10 PSI (truck tires) are recommended for speeds between 65 and 75 MPH. The extra pressure at high speeds is desired to reduce the amount of flexing within the tire as it turns. There is energy (heat) generated within the tires as they turn, and the tires can only dissapate so much heat per unit time. At high speeds, you want the tire to generate less internal heat per revolution - so you give it more internal air pressure.
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On Thu, 29 Jul 2004, SMoo wrote:

The sidewall doesn't say what to inflate them to. The sidewall says the *maximum allowable pressure* for that specific tire.

Most you could've spent on it is $90, and that's if you didn't shop around. Any idea what a *factory* service manual costs for an '85 Volvo? The answer has four digits *before* the decimal point.

Every tire they make is a piece of shit excuse. Next time get BFGoodriches.
DS
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Daniel J. Stern wrote:

But why would you WANT an 85 Volvo?
Matt
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On Thu, 29 Jul 2004 23:55:09 -0400, Daniel J. Stern wrote:

Who gives a shit? How is that relevant to this discussion? Are we supposed to be impressed, or something?

Better yet, get Goodyear.
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On Fri, 30 Jul 2004, Dan C wrote:

Obviously, you give enough of a shit to notice and comment on it.

*chortle* Good one! Got any more?
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Nooooooo, that the maximum they can handle, not what they should be!!!!! The common thinking from the pro's is to fill them to what the manufacturer puts on the door sticker. Adding much more than that can cause some of the vehicles to handle out of spec and can lead to rollovers, blowouts and other fun stuff.

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