[stvding]

Mine is an f32 xdrive.
I putnit in park and change my summer setup.
No hand brake involved.
Why i am able to spin the front wheels. Rears are locked.

[bimmer456]

Because only the transmission is locked. The diff in the front may not be and so spinning one wheel causes the other to spin in the opposite direction if your car is on a lift and you are spinning by hand. Also, being x-drive, the front drivetrain is disengaged under most driving conditions and power is only sent to the front axle when it is needed. So only your rear wheels are locked in park. Not sure if the diff would also be locked in the back or you can spin one wheel and the other turns in the opposite direction in the back.

[tpliquid]

Back locked probably caus it's engaged to park. And other side of car is not off the ground. U can let it free move when set to neutral

[stvding]

Originally Posted by tpliquid

Back locked when hand brake is on.

Please read.....i said, no hand brake involved

[stvding]

Originally Posted by bimmer456

Because only the transmission is locked. The diff in the front may not be and so spinning one wheel causes the other to spin in the opposite direction if your car is on a lift and you are spinning by hand. Also, being x-drive, the front drivetrain is disengaged under most driving conditions and power is only sent to the front axle when it is needed. So only your rear wheels are locked in park. Not sure if the diff would also be locked in the back or you can spin one wheel and the other turns in the opposite direction in the back.

I only have one wheel in the air... i used a jack

[tpliquid]

Originally Posted by stvding

I only have one wheel in the air... i used a jack

I edited my post.

[stvding]

Originally Posted by tpliquid

I edited my post.

For the front, i can spin it freely. The opposite front is on the ground. So no chance to move. I think the front axle is disengaged when P

[DDS2015]

This is normal. I can do this in all of the BMWs I do tire swaps on except the X1. I do an F32, F82, F15, F26 (X2), and F48.

Only in the X1 does the front wheel not spin when I'm changing over tires. The X1 has FWD bias AWD thus the front differential is the one used to hold the car when in park.

[Billfitz]

Originally Posted by bimmer456

the front drivetrain is disengaged under most driving conditions and power is only sent to the front axle when it is needed.

Under normal driving conditions the front axle is engaged, but only at 40% of the available power, with 60% going to the rear. That ratio can be changed as required, via the electronically controlled clutch that determines power distribution. My assumption is that when the engine is off the clutch position goes to the full rear/no forward axle position, and that's why locking the transmission only locks the rear axle.

[stvding]

Originally Posted by Billfitz

Under normal driving conditions the front axle is engaged, but only at 40% of the available power, with 60% going to the rear. That ratio can be changed as required, via the electronically controlled clutch that determines power distribution. My assumption is that when the engine is off the clutch position goes to the full rear/no forward axle position, and that's why locking the transmission only locks the rear axle.

But why bmw require to use a flat bit to tow xdrive? If in neutral, rear axle is disengaged and i assume front too. Should be able to tow with nose up, rear wheel on the ground with no harm

[Billfitz]

Putting the car in neutral means there's no connection from the engine crankshaft to the transmission output shaft. The drive wheels are never totally disconnected from the transmission. With the engine off you can rotate the front wheels, I did today, but there's still some resistance there so it's not totally freewheeling.

[Poon Stick]

I don't know how the xdrive works for sure, but speaking to my knowledge of the e46 AWD, I think the front may be connected via viscous coupling.

Basically if the rear slips, some (up to 40%) of torque is sent forward while rear is slipping. If this is the case on the f30, there is no real mechanical connection between rear and front wheels. So while being in Park locks the rears, when you spin a wheel on the front it'll either spin the opposite in the opposite direction or spin the driveshaft to the coupling

[HighlandPete]

Originally Posted by Poon Stick

I don't know how the xdrive works for sure, but speaking to my knowledge of the e46 AWD, I think the front may be connected via viscous coupling.

Basically if the rear slips, some (up to 40%) of torque is sent forward while rear is slipping. If this is the case on the f30, there is no real mechanical connection between rear and front wheels. So while being in Park locks the rears, when you spin a wheel on the front it'll either spin the opposite in the opposite direction or spin the driveshaft to the coupling

xDrive uses a multi-disc clutch pack in the transfer case, not a viscous coupling like the older designs. The clutch pack is open in the condition where the front wheel is jacked up, and as you say, no real mechanical connection in that state to the rear wheels.

[bimmer456]

When I first read the title I thought you were doing a front wheel burnout in Park I was like "whaa?" Lol

[stvding]

Originally Posted by bimmer456

When I first read the title I thought you were doing a front wheel burnout in Park I was like "whaa?" Lol

Lol

[HighlandPete]

Originally Posted by stvding

But why bmw require to use a flat bit to tow xdrive? If in neutral, rear axle is disengaged and i assume front too. Should be able to tow with nose up, rear wheel on the ground with no harm

One part of the clutch pack in the transfer box will be spinning and the other static, (front element), can imagine it would build quite a bit of heat if towed the way you describe.

[vooonoo]

Have you ever seen someone jack up a car to change their tire and forget to put the parking (hand) brake on? Some cars the wheels can still spin if the parking (hand) brake isn't engaged