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slbeemer
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Discussion Starter · #1 ·
I just bought new shoes for my care - Pirelli 225/55 R17. They put 42 psi in each of the four tires (tire guy told me that is what they are rated at). I noticed on the metal label inside the drivers door that BMW recommends 33 psi in the front and 41 psi in the rear. I have always put the same pressure all around but should I go with BMW recommendations and what are the implications of doing that?
 

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Yes, go with what the BMW door tag says initially. You can tweak to your liking from there.

The pressure stated on the tire itself is the max. rated pressure for that tire and really has no relation to the correct pressure for your/any specific car which is based on vehicle weight, suspension and passenger weight.
 

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I wanna DRIVE!
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In looking at tire pressures, you should know that the pressures that BMW recommends for the US are higher than the same vehicle recommendations in Europe. Because we Americans can't be trusted to check our tire pressures on a regular basis, it is safer to recommend higher tire pressures in order to reduce the likelihood of driving on dangerously underinflated tires. Thus, the 33/41 you are looking at is higher than the European pressures for the same vehicle of 29/33 for four people or less.

Note too that the front to back differential is higher in Europe than in the U.S. This is done not because we cannot be trusted to check our tire pressures, but is instead done because we cannot be trusted to handle a car when driving quickly around corners. The additional 4lb front to back differential in the U.S. is intended to induce understeer, which is less likely to get the inexperienced driver in trouble when driving fast around corners.

I've been running 36 all around for a little while, but I have some wear on the outer edges of my front tires. I think I'm going to try 32/36 for a while.
 

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Wrenchin'
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Depends on if you have the staggered setup [wider rear wheels] or if the tires are the same all around, me thinks. I've do 35/40 psi front/rear, staggered.
 

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Ohmess said:
I've been running 36 all around for a little while, but I have some wear on the outer edges of my front tires. I think I'm going to try 32/36 for a while.
Technical question, but why would higher front tire pressure lead to increased wear on the outer edges?

I would have thought higher pressure would translate to more wear in the center. Of course that's for straight line driving. Still, I would think lower pressure would cause more sidewall deformity and more wear on the edges, particularly with cornering.
 

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slbeemer
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Discussion Starter · #6 ·
thanks for the quick answers. I also question why higher tire pressure might cause wear on the outside edge of the tires.

A follow on to my question -- I do not have a staggerd setup so is a 35/40 or something close to that still appropriate. I assume the the door tag assumes that car doesn't have a staggered setup.
 

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I have done some research on tire pressure a couple of months ago. And looks like most people agree that the recommended tire pressure by BMW is higher than necessary and running at a lower pressure is more suitable to most US drivers.

I have a 2003 530 with Sports package. I have been running 32/36 and it worked well. The original 41 all around feels too bumpy to me not mentioned that I noticed more wear in the center for all tires, which indicated over inflation.
 

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Rob325_in_AZ said:
Technical question, but why would higher front tire pressure lead to increased wear on the outer edges?
It doesn't on my car. I was running about 33/36 (front/rear on a staggered set-up) and the outer edges of my fronts were wearing very fast. Increasing the pressure to 36/38 has slowed down the outer wear very substantially. The rears seem to wear incredibly evenly no matter what I do. I'll have gone through two sets of fronts by the time I need new rears.
 

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1Dreamer said:
It doesn't on my car. I was running about 33/36 (front/rear on a staggered set-up) and the outer edges of my fronts were wearing very fast. Increasing the pressure to 36/38 has slowed down the outer wear very substantially. The rears seem to wear incredibly evenly no matter what I do. I'll have gone through two sets of fronts by the time I need new rears.
Ah thanks.

I keep 38 all around on mine and have noticed generally very even wear. The first pair of tires lasted about 35k miles as I recall. These were the OEM tires with the e46 sport pack (ZR 17 225/45)
 

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Wrenchin'
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Ohmess said:
In looking at tire pressures, you should know that the pressures that BMW recommends for the US are higher than the same vehicle recommendations in Europe. Because we Americans can't be trusted to check our tire pressures on a regular basis, it is safer to recommend higher tire pressures in order to reduce the likelihood of driving on dangerously underinflated tires. Thus, the 33/41 you are looking at is higher than the European pressures for the same vehicle of 29/33 for four people or less.

Note too that the front to back differential is higher in Europe than in the U.S. This is done not because we cannot be trusted to check our tire pressures, but is instead done because we cannot be trusted to handle a car when driving quickly around corners. The additional 4lb front to back differential in the U.S. is intended to induce understeer, which is less likely to get the inexperienced driver in trouble when driving fast around corners.

I've been running 36 all around for a little while, but I have some wear on the outer edges of my front tires. I think I'm going to try 32/36 for a while.
We Americans also weight more, so that could be another reason for the difference in tire pressures.

Wear on the edges of tires is usually indicative of an alignment issue.
 

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BMW rec'ds make no sense (other than from a "safety" standpoint).
Less pressure in the front? The heavier end?

Less pressure in front = understeer. I think the lawyers got their hands in so the car's would push a bit more and hit head first.

Try puttig you tire pressure even all around and see how you like it. The car should turn-in better and handle a little better.

General rule of thumb is divide chassis weight by 100, then add a few psi to the heavy end, and subtract a few from the light end.
 

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What I am still trying to get is what the pressure should be. I have a 06 325i with run flats. The book does list my exact tire, the inside door has two stickers with different pressures and the Bridestone dealer gave me another set of pressures. Already burned through the fronts, because, according to BMW, the tire pressue was to low!

So, what is it supposed to be?
 

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nww2bmw said:
What I am still trying to get is what the pressure should be. I have a 06 325i with run flats. The book does list my exact tire, the inside door has two stickers with different pressures and the Bridestone dealer gave me another set of pressures. Already burned through the fronts, because, according to BMW, the tire pressue was to low!

So, what is it supposed to be?
Well as you can see, you're not going to get an exact answer. Different people have different preferences, and it depends on how much load you usually carry, and what your priorities are (ie, comfort? handling? tire longevity? etc)
 

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i have a 2001 E39 530i. with OEM rims and tire size setup of 225/55-16. I set the tire presssure to the door jam of 33 front and 41 back, this to me rode to hard and bumpy and nervous. I set the tire pressure all around to an even 31 psi, wow the car takes bumps so much better and seems to handle better.
 

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e39 tires pressure

I have a 18" wheels: front are 235/40/18, and the rear 265/35/18, what's the proper air pressur i should have. I had 17" befor, and i just changed my wheels to 18, and i felt a big difference in gas conssuming. pls help. thanx
 

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slbeemer
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Discussion Starter · #16 ·
I have the same 225/55 R16s and I have the same tag -- 33 and 41 psi. I tried that and didn't like the ride so I have gone back to 37 psi all around. I think 31 psi is too low - you will probably get tire wear you don't want. I would suggest something in the 35-36 psi range all around - this will be a nice mix between ride and performance. Good luck
 
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