facelift/pre-facelift & 1/2 model years??

[PropellerHead]

Originally Posted by TiAgX5

The torque split is fixed by the gearing UNTIL brake actuation causes the torque to the slipping axle to TRANSFER to the non-slipping axle.

Well aware of how Xdrive works.

You may be, but appear not to be aware of how a non XDrive/prefacelift AWD system works:

Originally Posted by TiAgX5

Not the case. Pre-facelift Xs were able to direct 100% of torque to front/rear axles and side to side using automatic brake activation.

This just isn't true. It should read "Pre-facelift Xs were able to direct fixed power of 38% to the front and 62% of engine power to the respective axle." You might have then offered that DSC/braking allows this transfer from side to side, but the ratio is the main thing that you have wrong.

I don't have any issue with how this happens- DSC enabled. Never said any different. What I said was that the face lift models with XDrive offer this up to 100% of available TQ to either axle. Pre-face lift X's do not. Plain and simple.

Here is a source from BMW that explains the difference. Pay attention to the 2nd and last paragraphs. The differences in the systems are clearly not what you think they are:

[TiAgX5]

Originally Posted by PropellerHead

You may be, but appear not to be aware of how a non XDrive/prefacelift AWD system works:This just isn't true. It should read "Pre-facelift Xs were able to direct power to 38% to the front or 62% to the axles."

I don't have any issue with how this happens- DSC enabled. Never said any different. What I said was that the face lift models with XDrive offer this up to 100%. Pre-face lift X's do not. Plain and simple.

Here is a source from BMW that explains the difference. Pay attention to the 2nd and last paragraphs. The differences in the systems are clearly not what you think they are:

When the DSC/traction control activates the brakes on a slipping axle where do you think that axles disrupted torque go? The other axle by chance? If you don't think that's the case you don't understand the basics of driveline dynamics.

[PropellerHead]

Originally Posted by TiAgX5

When the DSC/traction control activates the brakes on a slipping axle where do you think that axles disrupted torque go? The other axle by chance? If you don't think that's the case you don't understand the basics of driveline dynamics.

It may transfer there to fill the gap between the 0-38% (Front) or 0 - 62% (rear) of power delivered, but it cannot (and does not) vary on the older cars. The power doesn't 'go' anywhere- except away. The DSC system cuts the power if it exceeds the available traction that either axle can use.

Power is transferred dynamically (and electronically as opposed to physically) from 0-100% for either axle on XDrive.

[TiAgX5]

Originally Posted by PropellerHead

It may transfer there to fill the gap between the 0-38% (Front) or 0 - 62% (rear) of power delivered, but it cannot (and does not) vary on the older cars.

It does so dynamically from 0-100% for either axle on XDrive.

So in summary, you saying that when the rear brakes lock the rear wheels there's no more then 38% total torque from the transmission twisting the front wheels?

You do realize that if you try to explain it does not go to the front wheels, you are, in fact stating, BMW has negated Newtons first law of energy......Energy can neither be created nor destroyed in a closed system.

[PropellerHead]

Originally Posted by TiAgX5

So in summary, you saying that when the rear brakes lock the rear wheels there's no more then 38% total torque from the transmission twisting the front wheels?

I am saying that a fixed, split-ratio, gear-driven transfer case (like the NV 124 and NV 125 in non-Xdrive vehicles) will output power at a fixed ratio front to rear. That torque transfer ratio is 38 front, 62 rear and it is constant, not variable.

Electronic nannies (like DSC) and zillions of hypothetical situations can do what they want, but the physical gears and the static behavior of the NV124 cannot be changed. It just can't.

XDrive equipped models (ATC 500) come with a clutch system that allows this to vary up to 100%. It just does.

Edited to correct part numbers.

[TiAgX5]

Originally Posted by PropellerHead

I am saying that a fixed, split-ratio, gear-driven transfer case (like the NV 124 in non-Xdrive vehicles) will output power at a fixed ratio front to rear. That torque transfer ratio is 38 front, 62 rear and it is constant, not variable.

Electronic nannies (like DSC) and zillions of hypothetical situations can do what they want, but the physical gears and the static behavior of the NV124 cannot be changed. It just can't.

XDrive equipped NV125 models are chain driven with a clutch system that allows this to vary up to 100%. It just does.

I guess Sir Issac Newton was wrong. I guess the torque to that gear must take a bus to Hoboken, NJ or something like that.


The torque ratio is fixed ONLY as long as both front and rear gears are turning at the same rpm. When one gear is slowed or stopped the torque supplied to that gear transfers to the other gear in this universe.

[PropellerHead]

Originally Posted by TiAgX5

I guess Sir Issac Newton was wrong. I guess the torque to that gear must take a bus to Hoboken, NJ or something like that.


The torque ratio is fixed ONLY as long as both front and rear gears are turning at the same rpm. When one gear is slowed or stopped the torque supplied to that gear transfers to the other gear in this universe.

Where did I say that the TQ goes anywhere outside of the planetary gear? You're a little anxious.

Read again. I said it transfers and it does it at a fixed ratio. The gears turn at a 1:1 ratio- that is one spins at the same speed as the other. One has more teeth- the rear- and spins slower but with more teeth resulting in a higher ratio- all the time- than the other (the front)- that is smaller but with fewer teeth driving output. (I am prone to get the speeds/teeth mixed up, but the concept of a fixed ratio is the same despite my spatial deficiency) The gears spin at the same speed, but are different sizes resulting in different output front vs rear.

There is no clutch to vary the output of power within the transfer case on a non-XDrive car. Both spin at the same input/drive speed (1:1), but the output is different bc they're different sized gears. See below for an illustration.