Transfer Case stress - wheel diameter/tire pressure/wear

[fmugur]

I read a few threads about the tire pressure, the wear of the tires or the same brand/model and so on.
Since on the pre face lift model the transfer case is locked to a specific ratio to avoid pressure on the TC we have to make sure the diameter of the rear and front wheels are the same.

The 4.8 uses 35 rear and 32 front. Is the actual diameter the same at this pressure?
I tried to measure the diameter but I had some challenges finding a very flat and level surface.
Is the tire pressure on 4.6 as is on the 4.8 model?
Is the 4.6 TC different?

Can you please comment on this subject. Is the 35/32 tire pressure the combination the staggered tores end up to be at the same diameter?

[JCL]

35/32 is not related to staggered tire sizes, it is related to more load expected in the rear of the vehicle. You would need to measure loaded circumference, not unloaded.

[fmugur]

So the front has the engine, the back is pretty much unloaded since it's me only most the time in the car. Is having the same pressure front and rear an option for unloaded car?
I will do the measurement from the ground to the center of the wheel as in the picture again but last time I did I had to lower the rear tire pressure down to 27 to match the front hight.

[JCL]

Originally Posted by fmugur

So the front has the engine, the back is pretty much unloaded since it's me only most the time in the car. Is having the same pressure front and rear an option for unloaded car?

The same pressure (32 psi) is the starting point for all tire sizes on the 2000 model, up to four passengers. It is what I ran my 2003 X5 at.

[TwinTurboGTR]

Well the transfer case on the 4.6 used the mechanical TC as you mentioned and the 4.8 or anything in the 2004MY used the new X drive TC.

[Turbo_Bimmer]

You could use a tape measure, and measure from the ground to the top of the rims. If you have less than 1% of difference, your are within BMW specs. This way of measuring will take into account the tires inflation, wear and truck load.

[theblue]

you're not going to noticeably change the size of the tire by changing the pressures and even if you could it wouldn't remain constant as the tires heat up and cool down at different rates.

Try to find what cold pressure most have had good luck with and then watch for tire wear patterns to adjust as needed.

overall tire size can be different between brands and even models. The big reason to not mix and match tires all over the place is because of this difference. since the front and rear diffs are both open (from what I understand) I would only worry about matching tires on an axle.

[JCL]

Originally Posted by theblue

overall tire size can be different between brands and even models. The big reason to not mix and match tires all over the place is because of this difference. since the front and rear diffs are both open (from what I understand) I would only worry about matching tires on an axle.

Diffs are open but the transfer case isn't. Varying diameters front/rear has caused transfer case failures on BMW X models.

[theblue]

don't some models come staggered from the factory?

[JCL]

Yes, but with different size tires that end up being within a few revolutions per mile of each other.