[Florida-X3]

We have 245/50R19 105H M&S tires on our X3. The manual and door sticker say 33 PSI for fronts and 36 PSI for the rears. When I update iDrive with the proper tire size, it also say 33& 36 as the recommended PSI. However, after setting the proper tire size the car wanted to go through a pressure sensing cycle. After it was 100% done, iDrive was now saying 34 &37 was the recommended PSI. Not sure why iDrive changed its mind.

[SpencerPJ]

Darn good question. Given the ever so slight difference, I wouldn't lose sleep over it.

[g11hoonigan]

It changes depending on temperature. It's cute but totally unnecessary for most use-cases.

[Battin4th]

I'm part of the confusion club as well. Rarely does the "recommended PSI" ever agree with what's on the door sticker. Obviously the PSI on the door is the recommended cold tire pressure. And what's shown in the iDrive is constantly changing based on tire temperature. I think the whole implementation is quite ridiculous and confusing IMO. Depending on your tire size and type selections and then the <100 mph or >100 mph, I think the recommended PSI rarely agrees with what's on the door.

I think the general consensus here is, just go with what's on door when your tires are cold.

[Sportstick]

Originally Posted by Battin4th

I'm part of the confusion club as well. Rarely does the "recommended PSI" ever agree with what's on the door sticker. Obviously the PSI on the door is the recommended cold tire pressure. And what's shown in the iDrive is constantly changing based on tire temperature. I think the whole implementation is quite ridiculous and confusing IMO. Depending on your tire size and type selections and then the <100 mph or >100 mph, I think the recommended PSI rarely agrees with what's on the door.

I think the general consensus here is, just go with what's on door when your tires are cold.

It depends on what you carry. The door jamb sticker shows recommended tire pressure at the Gross Vehicle Weight Rating (GVWR), per NHTSA regulations.

https://www.jdpower.com/cars/shoppin...hicles-payload

If you carry a full load of passengers and cargo, the label values apply. If you typically are alone in the car, these pressures would be higher than necessary.

[Florida-X3]

The fact that it changes (iDrive recommendation) doesn’t make sense. Oh well, I’m sticking with sticker, manual and original iDrive recommendation of 33/36. I’m used to funky tire pressures, the TPMS was 4-5 pounds off vs. reality in our F15 X5.

[brettl]

I actually run non run flats (dws06) on the 19’s and run them at 37/45. Felt too soft at the door recommendation. Keep it kind of in the middle of the higher speed and lower speed idrive recommendation.

[nord1899]

Just remember the door card (and manual) tire pressures are cold. Meaning the car hasn't been used for a while, like say overnight.

iDrive is trying to adjust for temperature changes, as you drive the tires warm up and the pressure will change.

[bouchy]

The reality is, you don't have cold tyres when approaching gas station to reinflate (personal compressor was not a thing, Pepperidge farm remembers). So, either overinflate it a bit and then correct it at home with (proper) pressure gauge next morning, or respect what's stated in iDrive. iDrive values change a bit due to the temperature etc., but actual tyre pressure should move as well, if you drive. I don't think there is anything confusing. Check it in iDrive from time to time and spend your life with joy and your family.

Pressure gauges can cause some trouble, be sure you use something decent.

[Florida-X3]

Originally Posted by nord1899

Just remember the door card (and manual) tire pressures are cold. Meaning the car hasn't been used for a while, like say overnight.

iDrive is trying to adjust for temperature changes, as you drive the tires warm up and the pressure will change.

Not talking about the actual pressure, I'm talking about the recommended pressure. When you go into vehicle status, tires ... it provides the actual pressure reading from the TPMS but it also states what the recommended pressure should be. That's the number that's different from when you first tell iDrive the tires (size & type) you have. Not worrying about it but IMHO that's like looking at the door sticker and one time it says 33/36 and another time it says 34/37.

[g11hoonigan]

Originally Posted by Florida-X3

Not talking about the actual pressure, I'm talking about the recommended pressure. When you go into vehicle status, tires ... it provides the actual pressure reading from the TPMS but it also states what the recommended pressure should be. That's the number that's different from when you first tell iDrive the tires (size & type) you have. Not worrying about it but IMHO that's like looking at the door sticker and one time it says 33/36 and another time it says 34/37.

I think what we are saying is the 'recommended' pressure also goes up with the temperature.

All these stuff is all about speed. It won't really matter if the vehicle is run under 100mph @99% of the time.

While there are lab tests that give merit to this feature, it's more of a gimmick IMO. And there are (rare) cars that will even tell you the tire pressure is low for the speed you are running. Again, that's running way above 100mph, not just 120 or 130.

[Sportstick]

Originally Posted by g11hoonigan

All these stuff is all about speed. It won't really matter if the vehicle is run under 100mph @99% of the time.
.

Much of this is indeed about speed, but it is also about load, thus the door label for tire pressure when fully loaded with passengers and cargo. A tire underinflated for the load flexes the sidewall more and generates more deteriorating heat.

[g11hoonigan]

Originally Posted by Sportstick

Much of this is indeed about speed, but it is also about load, thus the door label for tire pressure when fully loaded with passengers and cargo. A tire underinflated for the load flexes the sidewall more and generates more deteriorating heat.

It depends and I don't think the iDrive recommendation calculates (adjusts) for the max load.

FWIW, SAE tests for 'speed rating' resulted in higher chances of survival when pressure is increased. Load was consistent all throughout.

[Sportstick]

Originally Posted by g11hoonigan

It depends and I don't think the iDrive recommendation calculates (adjusts) for the max load.

I very certain you are correct. This does place the burden on the driver to know the weight of the load versus the door jamb label limits, be it people or items. Perhaps this is unrealistic, but it is the only feasible metric for the OEMs and NHTSA and does allow some determination after an event if a vehicle is overloaded.

[g11hoonigan]

Originally Posted by Sportstick

I very certain you are correct. This does place the burden on the driver to know the weight of the load versus the door jamb label limits, be it people or items. Perhaps this is unrealistic, but it is the only feasible metric for the OEMs and NHTSA and does allow some determination after an event if a vehicle is overloaded.

I wish many drivers will become more aware and educate themselves, more than just operating the vehicle. Unless someone asks on a forum, these are rarely touched and often diluted in posts, usually when people go off on a tangent

[VrmmVrmm]

Originally Posted by Florida-X3

The fact that it changes (iDrive recommendation) doesn’t make sense. Oh well, I’m sticking with sticker, manual and original iDrive recommendation of 33/36. I’m used to funky tire pressures, the TPMS was 4-5 pounds off vs. reality in our F15 X5.

The sticker temperatures are the Cold tyre temps....standing at least 3 hours if you had a run. They then rise if you go on a journey...depending on speeds etc they will vary again....high speed motorway journeys the pressure recommended rises as does the actual pressure in the tyre....cold say 33 psi...fast run....36 psi will show up on tpms...

[Florida-X3]

Originally Posted by VrmmVrmm

The sticker temperatures are the Cold tyre temps....standing at least 3 hours if you had a run. They then rise if you go on a journey...depending on speeds etc they will vary again....high speed motorway journeys the pressure recommended rises as does the actual pressure in the tyre....cold say 33 psi...fast run....36 psi will show up on tpms...

I realize that but are you going to stop on your trip and say, "Oh, I better add a few more PSI" ....No, and if you do, you have to let it back out under cold conditions. I think most people (hopefully not being too generous) know that once their tires get warmed up and traveling, the PSI will raise 3-4 pounds.

I at least understand what BMW is doing, not sure it makes real life practical sense but time to move on. Thanks to all that have chimed in.

[lfdal54]

Here's a tidbit.

The iDrive controller rounds the numbers. If I read the TPMS sensors with my Autel scan tool I'll get a decimal point, i.e., 34.5. I can't remember if the iDrive system rounds it up or just truncates it. Also, the sensors themselves are generally somewhere between 2-3%. So at 35lbs on a good accurate gauge, you might be reading 34 or 36 on the iDrive screen. I try to set them all cold with a good gauge and then don't think about it anymore.

[Florida-X3]

Originally Posted by lfdal54

Here's a tidbit.

The iDrive controller rounds the numbers. If I read the TPMS sensors with my Autel scan tool I'll get a decimal point, i.e., 34.5. I can't remember if the iDrive system rounds it up or just truncates it. Also, the sensors themselves are generally somewhere between 2-3%. So at 35lbs on a good accurate gauge, you might be reading 34 or 36 on the iDrive screen. I try to set them all cold with a good gauge and then don't think about it anymore.

Again, it's not the actual iDrive reading I'm talking about it's what iDrive says is the recommended that's changing. I'm not worrying about it (never was) just questioning the moving target. I do have good gauges, have three (two different brands) and they all read the same. Thanks. This horse is dead.

[Leem40i]

As several others have stated, the only time you measure your tires to the spec on the door jamb is when the tires are cold. If you have 33 lb in the front tires once those tires warm up they will probably be closer to 35. When the door jamb says cold tire pressure it's referring to the tires having rested all night and have no internal heat built up.

[Florida-X3]

Originally Posted by Leem40i

As several others have stated, the only time you measure your tires to the spec on the door jamb is when the tires are cold. If you have 33 lb in the front tires once those tires warm up they will probably be closer to 35. When the door jamb says cold tire pressure it's referring to the tires having rested all night and have no internal heat built up.

Yes, I'm well aware of that.