[urbo73]

Taking delivery of my new 340i tomorrow morning, and was looking at what the tire pressures should be, to let them know to have it properly inflated for pick up.

The wheels are the 20" 795Ms and the tires the Pirelli P-Zero PZ4 RFTs, 225/35R20 fronts and 255/30R20 rears.

On the door jab sticker, it says (for under 100mph) to use 36psi front and 44 psi rear. See attached photo of sticker.

The owner's manual however says to use 42psi front and 44psi rear, both in the under 100mph section and over 100mph section. See attached screenshot as well.

So what's the deal here? 36/44, with a difference of 8 psi between front and rear per the door jab sticker seems like a large difference. Also the fronts 36psi vs owner's manual 42psi seem quite off at a 6psi difference.

Which to trust?

[lemetier]

Originally Posted by urbo73

Taking delivery of my new 340i tomorrow morning, and was looking at what the tire pressures should be, to let them know to have it properly inflated for pick up.

The wheels are the 20" 795Ms and the tires the Pirelli P-Zero PZ4 RFTs, 225/35R20 fronts and 255/30R20 rears.

On the door jab sticker, it says (for under 100mph) to use 36psi front and 44 psi rear. See attached photo of sticker.

The owner's manual however says to use 42psi front and 44psi rear, both in the under 100mph section and over 100mph section. See attached screenshot as well.

So what's the deal here? 36/44, with a difference of 8 psi between front and rear per the door jab sticker seems like a large difference. Also the fronts 36psi vs owner's manual 42psi seem quite off at a 6psi difference.

Which to trust?

The pressures calculated from the QR code data for each individual installed tire. This is scanned during PDI, transmitted to the car, calculated by the onboard systems, and then displayed in iDrive.

[urbo73]

Originally Posted by lemetier

The pressures calculated from the QR code data for each individual installed tire. This is scanned during PDI, transmitted to the car, calculated by the onboard systems, and then displayed in iDrive.

Yes, I saw that. But as the tires heat up (normal as you drive or as ambient temps increase), iDrive's recommended pressures also change and go up. Why is this? Once it detect the tire, which it correctly did, it should just state/show the recommended pressures and not fluctuate, unless I'm not understanding something.

[lemetier]

Originally Posted by urbo73

Yes, I saw that. But as the tires heat up (normal as you drive or as ambient temps increase), iDrive's recommended pressures also change and go up. Why is this? Once it detect the tire, which it correctly did, it should just state/show the recommended pressures and not fluctuate, unless I'm not understanding something.

Recommended Cold Inflation Pressure (BMW Printed Nominal Value) is based on 20°C/68°F; the white FMVSS label on the door jamb is the same temp but for maximum vehicle load on the rear axle.

With higher temps comes higher pressure. Since you have a post 7.2020 build, temperature compensation (both ambient and tire temp actual) is automatically applied and displayed appropriately. In cold climates, an advisory message is displayed if the pressure drops too low due to temperature.

Beyond temp compensation, with increased static vehicle loads, the recommended pressures displayed will adjust as well.

[urbo73]

Originally Posted by lemetier

Recommended Cold Inflation Pressure (BMW Printed Nominal Value) is based on 20°C/68°F; the white FMVSS label on the door jamb is the same temp but for maximum vehicle load on the rear axle.

With higher temps comes higher pressure. Since you have a post 7.2020 build, temperature compensation (both ambient and tire temp actual) is automatically applied and displayed appropriately. In cold climates, an advisory message is displayed if the pressure drops too low due to temperature.

Beyond temp compensation, with increased static vehicle loads, the recommended pressures displayed will adjust as well.

I understand how tire pressures work, and to inflate and measure when tires are cold, and to account for loads (doorjamb sticker is as you say for max to keep things simple) and for swings in air temperature, but I still don't understand why the recommended pressures should ever change. If the recommended pressure is 42/44, in this case for example, then that's what the tires should be set to when they are cold, irrelevant of ambient air temps or tire temps when driven (which go up). I guess I still don't understand why iDrive is doing this. I would think all iDrive should do is display the recommended pressures and display dynamically the actual pressures. Not sure why the former is also dynamic, especially if load is the same. Maybe if it detects a larger load, then it could recommend a higher pressure? It just seems confusing, where doorjamb or book is simpler.

[thakid22]

Originally Posted by urbo73

I understand how tire pressures work, and to inflate and measure when tires are cold, and to account for loads (doorjamb sticker is as you say for max to keep things simple) and for swings in air temperature, but I still don't understand why the recommended pressures should ever change. If the recommended pressure is 42/44, in this case for example, then that's what the tires should be set to when they are cold, irrelevant of ambient air temps or tire temps when driven (which go up). I guess I still don't understand why iDrive is doing this. I would think all iDrive should do is display the recommended pressures and display dynamically the actual pressures. Not sure why the former is also dynamic, especially if load is the same. Maybe if it detects a larger load, then it could recommend a higher pressure? It just seems confusing, where doorjamb or book is simpler.

I think people here are missing your problem...
The owners manual says inflate your front tires to 42 psi.
The door jamb sticker instructs you to inflate your front tires to 36 psi under *identical* circumstances.

One of those is in error. It is my opinion, that the door jamb sticker is wrong. It would not be the first time. The stickers were incorrect and recalled on certain E90 3 series back in the day.

The 42 psi is the correct pressure for the 20 inch front tires.
Running 36 psi up front will put you at risk on potholes, dull steering response, and make the handling a bit mushier up there.

Even the 225/40/19 PZero requires 38psi. So 36 psi, is surely too low for the even lower profile 20 inch.

If you feel like being a scholar, report your door jamb to your dealership. Might need to show it to an actual technician as a service advisor likely won't understand the severity of this being mislabeled. Other G20's are probably out there running around under inflated because of that label too. In normal driving it won't be an issue, but in the perfect storm it is an accident waiting to happen via a blowout or loss of control.

[urbo73]

Originally Posted by thakid22

I think people here are missing your problem...
The owners manual says inflate your front tires to 42 psi.
The door jamb sticker instructs you to inflate your front tires to 36 psi under *identical* circumstances.

One of those is in error. It is my opinion, that the door jamb sticker is wrong. It would not be the first time. The stickers were incorrect and recalled on certain E90 3 series back in the day.

The 42 psi is the correct pressure for the 20 inch front tires.
Running 36 psi up front will put you at risk on potholes, dull steering response, and make the handling a bit mushier up there.

Even the 225/40/19 PZero requires 38psi. So 36 psi, is surely too low for the even lower profile 20 inch.

If you feel like being a scholar, report your door jamb to your dealership. Might need to show it to an actual technician as a service advisor likely won't understand the severity of this being mislabeled. Other G20's are probably out there running around under inflated because of that label too. In normal driving it won't be an issue, but in the perfect storm it is an accident waiting to happen via a blowout or loss of control.

Yes, 36psi was definitely suspect for this wheel/tire. I since spoke with the service manager, and he did say there could be an issue with the door jamb sticker, so to trust the manual or iDrive recommendation instead. He said the same as you, that he's seen this happen before, where they put the wrong info on the sticker and then had a TSB or whatever and replaced the sticker. So you are correct.

Furthermore I spoke with him about iDrive and why it's changing the recommended pressures as tire temps fluctuate. His assumption is that it does that so that if someone decides to inflate when the tire is not cold, then they know what number to inflate to - it just adjusts as I would in my head I guess. For example if it's 90F out, and the cold, recommended is 42/44, and I know it will be mostly and consistently cooler by 20 degrees the rest of that day and week, then I would go to 44/46 or something, knowing the temps would drop. And I guess that's what iDrive is doing in reverse if that makes sense.

A lot more info, not sure it's entirely helpful for folks. I always adjust when tires are cold and take into account ambient temps. I will continue to do this. 90% of folks don't even bother with pressures, so not sure how iDrive's recommended pressures is useful. I like it for its ability to just show the actual tire temps and pressures in real time. I couldn't care less about its recommendations.