New wheel set up causing some transfer case issues

[dula]

Hey guys,

I just picked up a f15 35d. I come from the e92 and f30 platforms so I'm fairly used to this non sense.

I picked up some new wheels yesterday. BMW 215M wheels.

Front: 21x10 (or 10.5, i forget)
Rear: 21x11.5

I got some tires installed and they were P Zeros

Front: 275/40/21
Rear: 315/30/21

I drove on it for like 2 minutes and as soon as I got up 60-80km/h it felt like the transfer case was slipping and the front diff was binding almost. Got the chassis stabilization message and swapped back onto my OEM 20"s and the problem was gone of course.

F: 275/40/20
R: 315/35/20

Now from what I've found on these forums so far is that the 30-40 sidewall difference is too much and puts the car out of the xdrive tolerances. Makes sense. I also saw that some people suggested running 275/35/21 and 315/30/21 which would be within tolerances at 29.5/29.6

I'm just posting this in hopes that someone who is/has running/ran the set up mentioned above can confirm.

Appreciate the help.

[P1]

You are installing OEM wheels. Why would you not go with OEM tire sizes?

[jbfrancis3]

That's a 4% difference in circumference on the 21's - too much. The factory 20's are a 0.1% difference. I'd guess the tolerance is 1-2% or less. An unfortunate and expensive mistake.

[dula]

Originally Posted by P1

You are installing OEM wheels. Why would you not go with OEM tire sizes?

OEM these take a 325 rear which was a 2 week wait rn.

[stocktree]

I've never seen a all wheel drive car that allows you to have different tire diameters front to rear. Why do you think you can do that on the x5? The computer sees the front wheels spinning at a different rate than the rear, and throws the code.

[suitedcboy]

There have been some full time systems with a T case diff connecting front and rear driveshafts that didn't care (full size jeep wagoneers and cherokees and others). These don't have any control over torque proportioning like ours do nor do they have some software that changes torque split with higher computed engine torque and dial it down if the grip of front tires is more important than the drive torque applied to the front wheels.

[stocktree]

Originally Posted by suitedcboy

There have been some full time systems with a T case diff connecting front and rear driveshafts that didn't care (full size jeep wagoneers and cherokees and others). These don't have any control over torque proportioning like ours do nor do they have some software that changes torque split with higher computed engine torque and dial it down if the grip of front tires is more important than the drive torque applied to the front wheels.

True. With those older transfer cases, there were no electronics on them, so you wouldn't get any errors. But those transfer cases did have viscous couplers that allowed some slippage. But if they slipped a lot, the coupler would heat up and fail.

[Qsilver7]

Originally Posted by dula

I got some tires installed and they were P Zeros

Front: 275/40/21
Rear: 315/30/21

I drove on it for like 2 minutes and as soon as I got up 60-80km/h it felt like the transfer case was slipping and the front diff was binding almost. Got the chassis stabilization message and swapped back onto my OEM 20"s and the problem was gone of course.

F: 275/40/20
R: 315/35/20

Now from what I've found on these forums so far is that the 30-40 sidewall difference is too much and puts the car out of the xdrive tolerances. Makes sense. I also saw that some people suggested running 275/35/21 and 315/30/21 which would be within tolerances at 29.5/29.6

I'm just posting this in hopes that someone who is/has running/ran the set up mentioned above can confirm.

Appreciate the help.

You're running the incorrect size 21" tires. BMW recommends the sizes below for 21" staggered tires...or the 21" tire sizes you mentioned at the end of your quote above (highlighted in red) :

• Front: 285/35/21
• Rear: 325/30/21

[shimmy23]

Originally Posted by Qsilver7

You're running the incorrect size 21" tires. BMW recommends the sizes below for 21" staggered tires...or the 21" tire sizes you mentioned at the end of your quote above (highlighted in red) :

• Front: 285/35/21
• Rear: 325/30/21

i believe he knew that. he didn't want to wait for the proper tire sizes due to a 2 week delivery time.

OP, i dont think you'll find many if any folks that run different tire sizes then what is recommended per 21" OEM spec. I've seen folks run square setups, but again, that doesn't impact the TC like a staggered setup.

[sukhk527]

Your tire diameter is over the 3% the tcase likes and it’s complaining. Fix the tire sizes and recalibrate it and you’ll be fine. Otherwise it’s going to continue to complain.

[RED_Y_]

Originally Posted by dula

OEM these take a 325 rear which was a 2 week wait rn.

Between damaging your TC and waiting 2 weeks, I would go with waiting two weeks.

[P1]

Originally Posted by dula

OEM these take a 325 rear which was a 2 week wait rn.

Would you rather wait two weeks or damage your transfer case? Now you've damaged it and you'll be waiting two weeks.