[JayM40i]

So I looked through previous posts and still don’t have a great answer to this question. How are people choosing the appropriate tire pressure for their x7s equipped with all seasons on 21” wheels? Some posts say look at the door jam, some say use iDrive. I feel Iike the settings in iDrive for <100 mph feel soft and the settings for >100 feel way too high. Do people pick a number in the middle and if so, how do you determine the difference in PSI between front and rear. The range is different based on the settings you select. Thanks.

[ledphut]

I live in the land of potholes the size of asteroid craters (Chicago) so I always overinflate a bit.

As long as you’re within a healthy range of what iDrive is asking for just go with what feels right, which according to your post is somewhere in the middle of too soft/too hard.

[blutob2]

Originally Posted by JayM40i

So I looked through previous posts and still don’t have a great answer to this question. How are people choosing the appropriate tire pressure for their x7s equipped with all seasons on 21” wheels? Some posts say look at the door jam, some say use iDrive. I feel Iike the settings in iDrive for <100 mph feel soft and the settings for >100 feel way too high. Do people pick a number in the middle and if so, how do you determine the difference in PSI between front and rear. The range is different based on the settings you select. Thanks.

I select my tire in iDrive and been using that. Feels fine to me honestly. One issue I did have was when we had very cold temps recently, I got the low pressure warning. I aired them up according to iDrive and the warning never went away. Several days later, it was still there. The only thing I could do was change the tire in the settings and that recalibrated it, then I reselected my tire and all good now.

[jadatis]

Needed cold tirepressure is is to give tire a deflection warm that wont overheat any part of tire material, when driving the speed constantly, for wich it is determined.

For that load on tire and maximum speed used ( and wont go over for even a minute) is needed, and tiremakers organisations have a formula for that to calculate it, wich I got hold of end 2007, and went running with.

Maxload of personscartires is given for max 160kmph/99mph, but mostly rounded to the 100mph you read.

For higher speed, but who drives it, there is a system for highening up the reference- pressure of 42 psi for XL, you most likely have, before puting it in the base formula.

This " pigheaded Dutch selfdeclared tyrepressure specialist" now uses an other formula and system for speed, wich to my conclusions in time, comes closer to laws of nature.

So to answer your question next.
Give here your tire specifications, and I make you a cold pressure/ axleloadcapacity list, with build in maximum reserve, but still acceptable comfort and grip.
Need next.
1. Maxload or loadindex
2. Standard load ( AT 36 psi) or XL/ reinforced/ extraload ( AT 42 psi)
3. Speedcode, less important, shal be Q or above

Then give max used speed for the situation(s) , and give if wanted in psi or bar, kg or lbs.

Then you " ONLY'" have to determine the axleloads for the situation(s) 99% acurate, and search them back in my list for the needed cold pressure ( at 68 degr F/20 degr C ambiënt temperature).
The most tricky part in it all, and your responcibility.
And different axleloads give different pressures front and rear. Only driver front highest weight, fully loaded rear higher axleload so needed pressure.

The carmakers use GAWR's and 99 mph for comfort setting, and max technical carspeed for sports setting ( or whatever its called)
The the number of persons in car and luggage is also used for different settings.

Then there is difference of opinion between systems of what to use for the pressuresettings, and that gives the different pressures you read between car and app.

[cochese]

We’ve been running this, with the <100 setting and the low pressure warnings have gone away, and the ride feels ok.

Edit: these are cold numbers.

[bmwchicago]

I found this in the manual.

[MystroX5]

I run my AS 21” from PA to Florida at:
21” Front 33lbs. 21” Rear 39lbs
Or
21” front 35lbs. 21” rear 40lbs.

This is high speed highway driving on mixed surfaces from concrete to asphalt. My tires after 7K show almost no wear patterns.

[JayM40i]

Anyone using the >100 mph settings? Seems high but should I be looking at this as an option if I’m driving over 100 mph occasionally on the highway? I do mostly back road driving and some driving on the highway.

[cochese]

[QUOTE=MystroX5;30889446]I run my AS 21” from PA to Florida at:
21” Front 33lbs. 21” Rear 39lbs
Or
21” front 35lbs. 21” rear 40lbs.

This is high speed highway driving on mixed surfaces from concrete to asphalt. My tires after 7K show almost no wear patterns.


Same here with our AS 21s. Mostly 33/39 front/rear.