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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > All-Wheel-Drive (Xi / xDrive) Talk > What PSI do you run?



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      06-08-2016, 03:58 PM   #1
E9Slow
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What PSI do you run?

Hey guys just curious what you guys like to go by for PSI preference. I used to work for Firestone, so I know it's always standard procedure to go by the data on the sticker inside the drivers door instead of the tires "max psi" rating like many do, but I've also realized sometimes minor tweaks can make major improvements. My car is an '07 328xi sedan with pretty new Bridgestone Driveguard RFT (~10k mi) on the factory awd wheels (sorry forgot the 'type'). If I remember correctly the door reads like 32 front 34 rear or so for the car, but at that PSI (all were about 30-32) the car rode rough(-er than normal on RFTs) and when braking, would track wherever ruts in the road went and shake a bit. Today, just to experiment, I turned them all up to 40psi equally using a digital air compressor, and what a difference! It feels tighter, stays more true to a straight line, and when braking, there's almost no wandering at all, and the shaking is nearly gone! It still rides firm, but that's to be expected with the PSI turned up, completely worn out struts, and RFTs. Definitely found my new regular summer setting for these tires (until I finally upgrade wheels and tires).

Have you guys found different pressures that work differently for you, higher or lower than recommended?

(P.S.- I know a lot of my braking wandering is almost solely because of worn control arm bushings, but this did eliminate a LOT of what I was experiencing).
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      06-08-2016, 04:23 PM   #2
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this is really just a band-aid........if you dont really need the RFT i would ditch them next time you need tires. For reference im on conti DWS and run them at 38 psi all around. tried them at 40 and the car didnt like it too much with KW v1s. my next big thing is getting poly bushings for the front thrust arm hyrdo bushings (rear control arm in the front). fixes the front end stability
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      06-08-2016, 08:07 PM   #3
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Quote:
Originally Posted by niquehawk5
this is really just a band-aid........if you dont really need the RFT i would ditch them next time you need tires. For reference im on conti DWS and run them at 38 psi all around. tried them at 40 and the car didnt like it too much with KW v1s. my next big thing is getting poly bushings for the front thrust arm hyrdo bushings (rear control arm in the front). fixes the front end stability
That's actually what I've been researching doing next also heard good reviews about swapping out for the strong yellow bushing, would definitely like to try them as I prefer a tighter firmer ride anyways.
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      06-09-2016, 12:31 PM   #4
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I have them on my car and love them it definitely tightened up the front. When I brake there is no more shudder. It's definitely a great upgrade
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      06-20-2016, 10:24 PM   #5
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Quote:
Originally Posted by E9Slow View Post
Hey guys just curious what you guys like to go by for PSI preference. I used to work for Firestone, so I know it's always standard procedure to go by the data on the sticker inside the drivers door instead of the tires "max psi" rating like many do, but I've also realized sometimes minor tweaks can make major improvements. My car is an '07 328xi sedan with pretty new Bridgestone Driveguard RFT (~10k mi) on the factory awd wheels (sorry forgot the 'type'). If I remember correctly the door reads like 32 front 34 rear or so for the car, but at that PSI (all were about 30-32) the car rode rough(-er than normal on RFTs) and when braking, would track wherever ruts in the road went and shake a bit. Today, just to experiment, I turned them all up to 40psi equally using a digital air compressor, and what a difference! It feels tighter, stays more true to a straight line, and when braking, there's almost no wandering at all, and the shaking is nearly gone! It still rides firm, but that's to be expected with the PSI turned up, completely worn out struts, and RFTs. Definitely found my new regular summer setting for these tires (until I finally upgrade wheels and tires).

Have you guys found different pressures that work differently for you, higher or lower than recommended?

(P.S.- I know a lot of my braking wandering is almost solely because of worn control arm bushings, but this did eliminate a LOT of what I was experiencing).

I've got a square set-up with 255/35/18 PSS (non run flats) and typically run 34 at all four corners. I find this to be a pretty good balance between handling and comfort. That's with stock springs and Bilstein B6's. If I was at an autocross event (which i don't typically do any longer) I'd likely run the front at 38 or so. For a track day, I'd probably start 35 psi for the first session and then talk to an instructor about what the car was feeling like and where I was seeing tire wear - particularly upfront with a chassis that tends slightly toward understeer when pushed.

Now, all that said, tire pressure is a bit like shoes. You gotta determine what you're after, try it and adjust if necessary.

Seriously consider ditching the run flats if you can get a spare or goo/compressor set-up and don't mind the potential hassle involved. They're so much more comfortable for the handling you get.
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      06-21-2016, 10:13 AM   #6
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I've experimented with this a bit over the years with my 2007 328xi (even have some posts about my "adventures" with PSI). When I ditched RFT my Ventus V12 hated the door jam PSI numbers and bumping them to 38 all around fixed them. Sometimes I went to 40 but you feel everything. Oddly enough though, I'm now running 36 up front and 37 rear and seem to get better MPG and, of course, a more compliant ride (I have Micheline A/S 3 tires now, which are awesome). I don't feel a sacrifice in handling either. Now the MPG could be weather changes ( I also notice it happens when my average speed at fill ups is 40mph instead of 35mph. I thought driving faster was gonna lower it, guess not ). I also have Bilstein HD shocks.
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      06-21-2016, 01:56 PM   #7
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I run 36psi front, 32-34psi rear, cold.

I have a 17x9 255/40 square wheel/tire setup.

I have very bad snap/lift oversteer in my car so I run less in the rear.
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      06-21-2016, 02:02 PM   #8
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I had the same thing happen with my AS3s when I dropped my tire pressures. Somehow improved mpg.

I think I am currently running 38/36. I may drop it down to 36/35. I find, to an extent, that slightly more pressure in front than rear really helps neutralize the car's handling.
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      07-12-2016, 04:48 AM   #9
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34 front/36 rear. (cold @ 55*F)
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      07-12-2016, 04:51 AM   #10
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I run 8 psi in first and second gear and 20 psi on WOT
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      07-12-2016, 09:04 AM   #11
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Does it matter what size tires you run on front/rear if staggered? Or just go by what the door says?
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      07-12-2016, 11:32 AM   #12
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Quote:
Originally Posted by 550i Beast View Post
Does it matter what size tires you run on front/rear if staggered? Or just go by what the door says?
It all depends. For example if the door says 36psi, you need to check what stock tires were capable of (lbs) at 36psi. Let's say stock tires were rated at 900lbs per tire at 36psi; now you need to find out ratings for your new tires. If your new tires handle 900lbs at 32psi, you should run 32psi....
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      07-12-2016, 01:09 PM   #13
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38 is perfect for me with my 245/285 PSS tires.
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