Why 32 - 38

[DOrtiz]

Due to recent "slightly cold" weather in Florida (low 40s, oh boy ), my left tire pressure light came on (low pressure). So I decided to put some in and check them all while at it. They were all low actually, but what I found strange is the required pressure.

The door sticker calls for 32 front and 38 rear. Really?!?!? A 6psi difference? Why is that? I thought weight was practically eventually distributed. Maybe because it's an xDrive?

Thoughts anyone?

[0w40X1]

I don't get that either. My s28i says 35f 38 rear which is about right. If I run both 35 car doesn't want to turn, and with new Michelin PS4S it seems 35 37 works better.

Just try 35 front 38 rear and see. My fronts weren't wearing in center at 35 psi. The pressures they recommend for high speed are confusing. What they mean is those are pressure you might see after driving hard.

When fronts reach 42 psi hot they lose grip on either tires I've had. 40 hot front and 42 hot rear is sweet spot.

[DOrtiz]

Originally Posted by 0w40X1

I don't get that either. My s28i says 35f 38 rear which is about right. If I run both 35 car doesn't want to turn, and with new Michelin PS4S it seems 35 37 works better.

Just try 35 front 38 rear and see. My fronts weren't wearing in center at 35 psi. The pressures they recommend for high speed are confusing. What they mean is those are pressure you might see after driving hard.

When fronts reach 42 psi hot they lose grip on either tires I've had. 40 hot front and 42 hot rear is sweet spot.

Thank you.

I put 32/38 as suggested and for the life of me the car seems smoother and strains less on initial takeoff. Of course, this could very well be butt-dyno syndrome.

I will say initial pressure tests showed 28/32 if that makes a difference? 😳

I don't drive her hard. I cruise her 90% of the time. Once in a while to overtake a truck or something I make her roar but aside from that it's mostly smooth sailing. 😊

[LevinBR]

This pressure spec from BMW is to induce under-steer (vs over-steer) for safety reasons.

[DOrtiz]

Originally Posted by LevinBR

This pressure spec from BMW is to induce under-steer (vs over-steer) for safety reasons.

Thank you Levin.

I'll need to Google that so I know what it means. 😊

[DOrtiz]

Got it! 👍🏻👍🏻

"Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occurs when a car steers less than the amount commanded by the driver."