ThetaTau87

Many people (even the makers of the Stasis high bias torsen diff) believe that if you are ever in a situation that a wheel is in the air or you have zero grip at one axle that the car will not move. This comes from the misconception that the torsen diff multiplies the grip available at the slipping axle and sends it to the axle with more grip. This is not true. Saying that grip at the wheel and torque at the wheel are the same is wrong. Grip at the wheel is not torque at the wheel. I have argued my point many times on this forum, but have always had others tell me I was wrong.

I figured I would settle this once and for all. I jacked up the rear of my car with both rear wheels off the ground. I was able to move the car forward and backward. Watch the video for proof.

You can say that the torsen diff multiplies the torque going to the slipping axle by 2:1, but the minimum torque sent to that axle is 33% of the available engine torque, not the grip at the wheel. Therefore, multiply that by 2 and the remaining 67% of the torque goes to the non-slipping axle. A better way to say it is that the torsen diff splits the available engine torque between the front and rear axle and the max torque split it can send to either axle is 2:1 or 67%/33%. The wheel can have zero grip and still will have 33% of the engine torque going to it.

Actually the torsen diff works with no direct connection to grip. It only reacts to changes in axle speed front to back. A change in axle speed is caused by a loss of grip. A loss of grip causes that wheel to spin faster and the diff compensates by sending more torque to the slower axle until they are spinning at the same speed again and the torque split is at 50/50 again. It senses how much torque (by axle speed) can be sent to that axle and adjusts it constantly. You can see in the video the rear wheel on the opposite side is spinning faster than the speed of the car. Only one rear wheel spins because the rear diff is open.

I hope this clears up a long standing misconception about quattro.<ul><li><a href="http://www.hostdub.com/albums/thetatau87_album01/Tire_in_Air_Video.mov">Watch the video here!</a></li></ul>

The Crapple

:golf clap: bravo!

EvanUrS4

Nice work, that ought to shut everyone up =)

Smitty: Kriegswagen

That's a very nice garage.

escargot

The wheel was on the ground, but the axle popped out. The car wouldn't move an inch. Tried locking the rear diff - nothing.

Mike2kS4

If so, torque will definitely go to the fronts.

On newer quattro cars the EDL's will prevent the potential "stuck" scenario from happening anyhow.

TabulaRasa

#1. Was that your throwout bearing making noise? #2. Lube your door hinges. =)

RMN

look closely and you'll see that the passenger side rear wheel does rotate

closed loop

The Torsen does split the engine torque, but the torque at any given wheel is definetly a function of the torque at the lowest wheel, not directly related to the engine. With a Torsen with a 2:1 torque bias ratio (TBR), if the torque on the lowest wheel is 100 Nm the torque on the opposite wheel would be 200 Nm. If the wheel truely had zero torque then the opposite wheel would also have zero torque. In the real world there is friction, and inertia, so zero torque is not acheivable. The left over engine torque that isn't going into driving the car is being turned into inertia by spining up a wheel. An open differential operates on the same principle, but it has a TBR of 1:1. (Even open differentials have TBR's from 1.1-1.3, because of friction, but it is easier to explain by ignoring friction). Your car is able to drive forward and back, not because of engine torque, but because 2.x times the torque being reacted by friction and inertia in the rear is being transmitted to the front. Because I can push my car forward and back in my garage it doesn't take much. Park your car on a 10% grade, jack up the rear and try to drive up that and I'm guessing our cars won't make it.
That being said Torsen's are an awesome coupling technology, because they react "instantly" to torque changes at the wheels, where even good electronic systems take upwards of 500ms to react torque. A Torsen is a driver's AWD.

The Crapple

you just described what would happen if the car had an open diff for the center, not a torsen.