how do you know what psi to run

[ahoier]

I typically meet somewhere in the middle. My "placard" (owner's manual) calls for 32 psi) - but my tires "spec" 42 psi MAX COLD....so I use 36.....ride is great. I've tried 42 PSI.....and the ride was just too harsh lol.....not worth the extra couple cent, gas savings

 

[bdcardinal]

I almost think that the book is trying to say to go 1-3 under the door sticker when cold in hopes that when the tires heat up they will be at the proper pressure.

What is the book title and publisher, I would email them or the author and ask for clarification and sourcing. I find it very odd that a text book would stick their neck out and say to do something that differs from the owners manual. It could open the publisher and author up to lawsuits.

Also was the Firestone rep from a Firestone store or from the actual Bridgestone/Firestone corporate office. I ask because I have heard some tire shop people at chain places say some real off the wall things.

 

[Dakota1820]

He was from a corporate office

 

[GC4lunch]

Originally Posted By: Doog
Placard on door plus 2psi. The Firestone guy is a moron.

^^ this

It is a very rare tire that does not lose a pound of pressure per month; some tires lose more, a few lose less. If you fill only to the door placard pressure and you do not check and top off your tires every two weeks or so, you probably will be running a tad low most of the time.

Running at below the optimum pressure generally causes some irksome problems, while running a little bit high causes none. Within the maximum tire pressure (listed on the sidewall, usually either 44 psi or 51 psi), the higher the pressure, the greater load carrying capacity the tire has. Running the tire low, especially with a heavily loaded vehicle, will cause the tires to heat up (from friction caused by flexing in the sidewalls), increasing the probability of tire failure (blow-out). It also will cause both outer edges of the tire to wear faster than the center of the tread, even faster than running tires on Macpherson strut suspension systems causes one outer edge of each front tire to wear faster that the other outer edge. Finally, the placard recommendations of the vehicle manufacturer are notoriously biased low, because that gives a softer boulevard ride; usually handling (lateral adhesion) will be improved if you boost the pressure a couple of psi, though at the cost of a very slightly harsher ride.

 

[Garak]

Originally Posted By: The Critic
Not sure what the Fartstone guy was thinking.


He was thinking of Firestones that had catastrophic failures at highway speeds in certain SUVs when they were underinflated.

 

[expat]

Originally Posted By: bdcardinal
I almost think that the book is trying to say to go 1-3 under the door sticker when cold in hopes that when the tires heat up they will be at the proper pressure.

What is the book title and publisher, I would email them or the author and ask for clarification and sourcing. I find it very odd that a text book would stick their neck out and say to do something that differs from the owners manual. It could open the publisher and author up to lawsuits.

Also was the Firestone rep from a Firestone store or from the actual Bridgestone/Firestone corporate office. I ask because I have heard some tire shop people at chain places say some real off the wall things.


Agree!
I would take this up with your instructors.

Many vehicle manufacturers state a different tire pressure Front and Rear, As tire pressure effects the vehicle handling.

I can think of some cars (my Triumph for example) where you would be VERY foolish NOT to maintain the stated F R pressure differential!


The Firestone guy was a Moron!

 

[TallPaul]

I don't know what the owner's manual says, nor the placard. Most of my tires say max somewhere in the mid 40s. I have been pumping them up to about 37 psi. If the middle treads start wearing faster, I can reduce the pressure a few pounds. But they usually reduce several pounds by the time I get around to checking them again.

Higher pressure should help fuel mileage too.

Really, the tire manufacturer should provide a chart of pressure per weight. Of course then we are talking about weight on each individual wheel. Does anyone put different pressure in the back which is lighter than in the front?

 

[MrQuackers]

I have an SL2 and run about 40 psi. Tires (Sumic GTA) are rated @ 51 psi max. No problems slaloming the country roads in the rain over the roadside recommended cautionary curves limits. Like riding a rail. Love Saturn.

 

[bvance554]

Here is my take on it....

The maximum tire pressure listed on a particular tire is the maximum pressure that the tire can safely be operated at. The textbook says to inflate the tires to 1-3 psi less than the maximum when cold so that it does not exceed the maximum when heated. This is correct for the tire without any regard to the vehicle.

The tip states to inflate it to the specified pressure in the owners manual, which is what should be followed. It is two different points of view. The tire manufactures' safety limit, and the vehicle manufactures' reccomendation for best performance.

 

[Kuato]

Originally Posted By: antiqueshell
Originally Posted By: Doog
Placard on door plus 2psi. The Firestone guy is a moron.


x eleventy billion!

If you run nearly max pressure with the standard tire sizes you will probably destroy the suspension in short order, and your teeth will likely be shaken out of your head too. Not only that you actually will greatly increase tread wear towards the center of the tire tread.


As far as aftermarket tire and wheel sizes, you usually go thinner profile and wider so in effect the pressures would stay about the same for up to +2 I would guess.


No. Inflating your tires to their max pressure will NOT destroy the suspension and will not knock your teeth around. However the ride is firmer.

I can't agree with your wear estimate, and have found the opposite to be true -- for years I ran the placarded pressure and usually ended up with worn outer edges of tires and not much wear in the center.

Can we all agree that a properly inflated tire will show even wear across the entire tread? If so, then choosing an arbitrary number listed on the door panel or anywhere else isn't correct -- everyone's saying use this or that number but I didn't see any real world testing. You've got to play around with it to get the proper pressure for your vehicle.

For my last 8 vehicles (the 2 in the sig, 2008 Nissan Versa, 2000 Grand Cherokee, 2004 Dodge truck, 1986 Mercury, 1996 Jeep Wrangler, 1993 Ford Crown Vic) I have found that inflating the tires to their maximum value provided even wear across the tread. For some of the vehicles,there was excessive wear on the edges. For NO vehicle was there more wear on the center of the tire.

In each case, the inflation pressure was a good bit higher than the placard on the door frame. Manufacturers often placard a tire pressure that give the best ride...a firm ride isn't what Mr. Old Guy wants in his car, he wants it cushy and may not care about tire wear.

For me, the history I have over the last 300,000 miles of driving the vehicles listed above shows pretty conclusively that a higher pressure gives more even wear. Finally, in those miles I experienced exactly ZERO suspension issues.

 

[Dakota1820]

I have my saturns set a 35 and outside wear is a smidge more than inside.

 

[The Critic]

Originally Posted By: chevyboy14
I have my saturns set a 35 and outside wear is a smidge more than inside.


33F/29R worked great for me when I had my '96 - OE spec is/was 30F/26R.

 

[krzyss]

Originally Posted By: TallPaul
Does anyone put different pressure in the back which is lighter than in the front?


I do if this is what placard says.

Krzys

 

[KitaCam]

First of all, well done Chevy for noticing this apparent contradiction of information....said as a former teacher...some say always a teacher...

I always expected my students to notice this type of "expertise" offered and taught them to "question authority" of the authors when their own experience taught them otherwise...

This is not to say that I taught students to say that such authoritativeness was automatically wrong and that they were automatically right, but taught them to ASK WHY there was this conflict between their knowledge and the text knowledge....

You could bring in this thread to class and declare the authors idiots...but...that would only bring in more anecdotal experience to support one view over another...but experience is not knowledge unless supported by research...

You can say you've done some of YOUR OWN research of knowledgable car owners and since nearly all disagree with the tire manufacturers and some who modify the car maker's recommendation, you want to know WHY....

[even though everything I know about tire pressure supports what you've read here...and answer why you should follow car manufacturers and not tire manufacturers....and answer the quesstions I pose below, ask you prof....]

.....you should 1st ask your prof. WHY the tire manufacturers would tell car owners such general information that is so different from car manufacturers.

.....you should ask why the tire manufacturers recommend the PSI settings that they do...what is THEIR PURPOSE for such a variance from car makers' PSI settings...

....you should ask your prof what is the impact of different PSI settings on tire wear and function, and on the car's performance.



THAT is the role of a good student...to ask why...

 

[Hokiefyd]

This is very simple. Call the customer support phone number for any number of tire manufacturers, and ask them what pressure you should use in your tires.

Hint: they will all tell you to use what the vehicle manufacturer specifies, as long as you are using tires in the correct size/specification. If you are deviating from that, then there is certainly reason to adjust accordingly.

 

[CapriRacer]

f you were to call a certain tire manufacturer and ask to speak to an engineer so he could explain WHY we (as a tire manufacturer) recommend what we recommend, you MIGHT talk to me. Needless to say, I find this whole thread very, very interesting.

I realize that some think the tire dealer speaks for the tire manufacturer. They do not.

Some think the tire dealer is knowledgeable on the subject. Some are, some are not.

Some think that ANYONE employed by a tire manufacturer has enough knowledge on the subject. They do not. I can tell you that even our sales folks have lots of the same mis-conceptions the general public has.

Bottomline: The vehicle tire placard if the tire size is the same as listed there.

Additional info: If you were to test a number of different tires, you will find that they behave differently under the same pressure. That's a difference in the design characteristics of the tire. That is intentional. Some tires are designed to ride better than others. Some are designed to have crisper steering. Don't expect tires to feel EXACTLY the same way. You have to select tires with the characteristics that are important to YOU - keeping in mind that there are trade offs and you can't get everything you'd like.

 

[cchase]

Originally Posted By: chevyboy14
Originally Posted By: Quattro Pete
Originally Posted By: chevyboy14
My text book. It says most tire manufacturers say to run between 1 and 3 psi below max psi when cold.

Can you provide an exact quote from your book?



http://i1090.photobucket.com/albums/i377/dakota1820/IMAG0024.jpg


Hope its readable


The wording here states that the number on the sidewall is the maximum pressure, but to ideally run at the pressure listed in the vehicle owners manual.

The purpose of the last paragaph seems to be to say that even though the tire has a maximum inflation pressure, inflating the tire to a pressure 1-3 psi below this is recommended (if you're going to run at max sidewall rating).

 

[eljefino]

Originally Posted By: cchase

The purpose of the last paragaph seems to be to say that even though the tire has a maximum inflation pressure, inflating the tire to a pressure 1-3 psi below this is recommended (if you're going to run at max sidewall rating).


I agree on the confusing yet possibly not self contradictory editing. Seems like they had to put all that in the book to make it thicker and more saleable.

Back in the day you could find different inflation pressures for high speed use or lightly vs fully loaded. My 1994 dodge spirit had this, for example. Figure CAFE or Ford/Firestone put the keibosh on that, or they think we're dumber now.

Personally I have 30/26 on my saturn and can't buy a tire that takes less than 35 on the sidewall. Like having the extra capacity. I run somewhere between placard and sidewall for my own reasons, Due to

-- wild swings in temp this time of year (every time of year?)
-- would rather adjust pressure on a warm/nice day so it's adequate in the cold
-- air can leak out, but never leak in
-- I like how it turns with stiffer sidewalls and more air.

That said I get even wear, but might anyway. I probably have that "cap ply" that keeps the center from bulging out too much more.

 

[Dakota1820]

I found out that the reason a lot of firestone tires failed was because people ran than above 10% below the max rating thus effecting the tire with to much heat and ruining the glue atleast that is what I was told and firestone was dumb enough to write it down In emails . I set my tires at about 40 today the wide is firmer but it feels better than 35 I think 38 is probably going to be perfect mind you my Saturn tires are a little wider than stock

 

[Dakota1820]

I found out that the reason a lot of firestone tires failed was because people ran than above 10% below the max rating thus effecting the tire with to much heat and ruining the glue atleast that is what I was told and firestone was dumb enough to write it down In emails . I set my tires at about 40 today the wide is firmer but it feels better than 35 I think 38 is probably going to be perfect mind you my Saturn tires are a little wider than stock