Quote:
Originally Posted by M2siast
I had been suffering from high fuel consumption, highway wandering (had set M2 to Sport+ chassis to firm up the drive and control the wandering), and very poor wet grip (Pirelli Pzero).
I noticed my car came with 32 psi all around… and I’m not sure why BMW would do that…
I have since corrected my tire pressure to
- 40 front
- 45 rear (I like to put 1 psi over because I inflate them in a warm garage, and it’s getting cold out, so it accounts for the loss of pressure coming out of the garage)
Now my car:
- is great on the track (already was)
- feels lighter
- has better turn in (I thought the turn in was great before, oh what I missed, the sharpness is amazing now)
- has unbelievable wet grip (no slide whatsoever; whereas before I couldn’t really use throttle and turning was sketchy because of the loose rear)
- has better fuel economy (combined with me changing gas from Shell to Chevron, which I expected)
- has a sportier ride without being uncomfortable
Any guesses as to why BMW would set the pressure so low?
What are you guys running and have you played with the different tire pressures?
I’ll stick to this recommended setting for good.
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BMW sets the tire pressures based on max speed, load, and package and wheel/tire combinations. I'm sure BMW receives some input from the tire makers and does some field testing: track and road; to ensure the tires do not manifest any abnormal (side wall or center) wear under varying speeds and load conditions.
32psi is not low for those of us owners that have the tire/wheel setup for which 32psi is the recommended pressure. Oh, and keep the speed below 100mph...
40/45 is way high unless you are carrying the Olympics weight lifting team on a run around the 'ring...
Or you have the M package and are running 285/30 20" and 295/20 21" tires. At >100mph the manual calls for these to be inflated to 44psi and 48psi respectively.
My car doesn't have the M package and has the 19"/20" tire combo and I don't but very seldom and then not for but just a brief instant or two take the car above 100mph.
Thus I follow the owners manual -- which someone has already posted -- and for my car/tires it is 32psi "cold" provided 100mph is not exceeded. (If I drove my car fully loaded or tracked my car I'd certainly check the owners manual for how much pressure to run fully loaded or if I exceeded 100mph for any significant time.)
With 32psi is the tires I don't notice any issues. Gas mileage is reasonable. Really though the tires would have to be considerably under inflated to affect gas mileage. Far and away the biggest factor in gas mileage is vehicle usage.
The ride is firm but not jarring or harsh and the tires even when I press the car on curvy roads manifest considerable grip.
Unless you are running tires for which BMW calls for higher inflation pressures and the pressures you have selected are within BMW's recommended pressure with the tires inflated as high as you have then inflated I would expect sub-par contact of the tread to the road. And I would expect after awhile the tires to show excessive wear in the center of the tread.