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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Square setup=same tire psi all around too??



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Wheel offset calculator courtesy of BimmerPost.com. You may use this calculator to calculate what tire sizes you might need if you upgrade your tires, or what wheel sizes/offsets are compatible with your car.
    Current Wheel Width  inches             Current Wheel Offset  mm.
         New Wheel Width  inches                  New Wheel Offset  mm.
 
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Original Tires Diameter (in.)
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  Difference in diameter (in.)
           Percent Difference %
                     
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      08-27-2012, 08:19 PM   #1
ziominix
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Square setup=same tire psi all around too??

Switched to 235-40-18 all around on new wheels obviously. Should I maintain the factory tire psi specs with higher pressure in the rear or run same psi all around now??

Thanks for any input.
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      08-28-2012, 12:58 AM   #2
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No ideas?
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      08-28-2012, 02:36 AM   #3
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I use a square setup with 235 all around. I suggest to front pressure should be lower than the rear. Too much pressure in the front makes the ride very poor. I recommend the fronts around 36-37 and the rears 38-39, but you may prefer lower pressure for softer ride quality.
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      08-28-2012, 11:06 AM   #4
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Depends on if your tires are rft or not. If they are rft, go with BMW's recommendation; if non-rft, add 2-3 psi to the front tires from what BMW recommends.
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      08-28-2012, 11:16 AM   #5
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Start with the OEM pressures and experiment from there. Decreasing the front/back differential will tend to reduce understeer but will make the car less stable at speed, especially in crosswinds.

The non-staggered 16" tires on my E91 call for 32/39 but I prefer 34/37 when the car is lightly loaded and 34/42 when carrying 1/2 ton of stuff.

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      08-28-2012, 04:37 PM   #6
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It would be no problem to stick with the factory psi recommendations, run flat or no. Some prefer slightly higher pressures for faster steering response when going to a non run flat, but it is not needed.
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      08-28-2012, 04:46 PM   #7
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Yeah not running run flats. Pole position 970AS. Would equal pressures for same size tires not lead to more even wear characteristics?
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      08-28-2012, 06:58 PM   #8
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2011 BMW 335i  [4.66]
Quote:
Originally Posted by ziominix View Post
Yeah not running run flats. Pole position 970AS. Would equal pressures for same size tires not lead to more even wear characteristics?
No. Only if the pressures are extremely off would there be wear problems ...and wear would be the least of your worries at that point.

Start from stock pressures listed on your driver side door and go from there as noted. I run 34 front, 38 back, almost stock with my non RFT. Perfectly fine.
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      08-28-2012, 11:00 PM   #9
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On my door jamb, it reads for speeds up to and over 100 mph, recommended setup is 39psi front/45psi rear, a 6psi difference between front and rear.

I run a COBB tune, so the higher pressure in the back helps with grip, but I run 36psi front/42psi rear for a softer ride (hehehe) and in anticipation of temperatures increasing the inflation plus or minus 3psi front/rear.

I also have a Quaife diff, so I like to drift with the higher pressure.



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