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Discussion Starter · #1 · (Edited)
Sick of center tire wear and throwing money away, I decided to bring in my camber as close to zero as possible (dealer took it to -1.0°) and run 27 PSI on all my tires against the instructions on the door jamb sticker and against the manual.

I ran into a senior tire engineer from Bridgestone (I live near Akron, Ohio.. "rubber city USA") while I was getting my windshield replaced. I told him how my tires (especially rear) always had extreme center wear running the recommended PSI. He took a moment to look at the GVWR front/rear on my door jamb, then looked at my tire size and recommended I try 27 PSI cold.

What I noticed immediately is that the car handles more predictably, ruts (at intersections) don't fight back as much, and the ride is smoother and quieter. Not sloppy at all. Since I rarely take the car above 100 MPH, this lower pressure seems suited for me.

I took a look at my tire wear tonight and to my amazement, the center tread is wearing much more evenly now compared to running the recommended pressure from BMW, 29 Front, 34 rear. I know all about tire pressure differential and handling, but I really think the recommended PSI is artificially high due to the 1990's Ford Explorer/Firestone controversy. I see no sign of tire stress or overheating and the fact that my tires look much healthier at this pressure has me convinced.

Before, 15K miles, recommended PSI, factory alignment specs. If you look at the wear bars, you can clearly see the huge amount of center wear:



After, 10K miles, lower 27 PSI, camber set to the most positive number the dealer would allow (-1):

 

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Whats youre tire profile ?
 

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I run 35 PSI all the time , slightly higher when autocrossing. and have even wear, you must need more practice reading a pressure gauge because i dont think u where running the correct pressure and getting weird wear
 

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42R, 38F Nitrogen in mine and no such wear. Radials should always be
32 PSI minimum, at least that's what the rule used to be..
 

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Premature center-wear is usually indicative of over-inflation, whereas side-wear would be of under-inflation - which is kind of confusing because you're under-inflated and getting the symptoms of over-inflation. I'm not sure how this senior engineer can suggest 27psi off the top of his head considering that proper air pressure is dependent upon the weight of the car. Regardless, incorrect camber will promote excess wear against one edge or the other - your outer tire is now going to wear faster.


Honestly I would inflate tires properly and get a stock alignment - unless you're using non-standard wheel sizes, in which case I couldn't begin to tell you what is appropriate. From there if it is still wearing premature, something else is wrong and I would get your suspension checked.
 

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Just curious, and I ask without any intent to insult your intelligence, but have you checked with different gauges or have you always used the same tire pressure gauge when filling tires?
I use three of them. :b:
 

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It's probably to do with the tires themselves. Different tires require different pressure, quite possibly also affected by the tire age.

When using the recommended pressure, I found my old PS1 tires looked less round than my new PS3 tires.
 

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15-20K miles isn't unusual for Max / Ultra performance tires. If you want better traction you give up tire life.

What are the specs on your tires and wheels?

If you went to a higher "load index" say from 91 to 94 you may need a lower pressure to carry the same load. (matching the specs for the factory tires)
If you change the load range, from XL(extra Load) to SL(Standard Load) you may need a different pressure.
If you have tires mounted on wheels that are less than the "measured" wheel width for the tire, it will tend to give you a "rounded" contact patch, less wear on the edges and more in the middle.

This is a very good document on tires.
http://www.tiresafety.com/images/Tire Replacement Manual.pdf

Find the actual load carried from your factory tire pressures, and then use that to find the correct tire pressure for your new tire size/load index.

Using the info from my 2003 330Ci owners manual-

205/50/17 93XL
front tire pressure (normal load) 33psi shows a load of 1190lbs (appendix B tables)
rear tire pressure (normal load) 38psi shows a load of 1312lbs

If I compare loads above to a 245/40/17 91 SL tire in the chart -
1190lbs indicates a new front pressure of 31psi front and 1312 lbs gives 35psi rear (BMW doesn't show this size for the front in the owners manual)
The 35 rear pressure matches exactly the pressure recommended by BMW for that tire size in the manual, even though it doesn't list the load index.

If I stuffed 255/40/17 94 SL tires on-
1190lbs indicates a new front pressure of 28psi front and 1312 lbs gives 32psi rear (a little over the 1312 lbs)
 
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