For the attention of Teutonic_Tamer.Please note that Staffan has been employed by Haldex Traction in Landskrona since August 97. He works as a control software developer on the Haldex Limited Slip Coupling. This is an intelligent coupling for distributing the torque between axles in an all wheel driven vehicle.
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Hi Staffan,
I'm trying to settle a debate about the Haldex Gen II Controller fitted to my Golf MkV R32. As a person with extensive knowledge of these systems, would you mind answering the following question?
Can the Gen II Controller transfer more than 50% to the rear wheels in a front engined car?
Person A believes it can send over 50% of the engine's torque to the rear.
Person B believes the only time a Haldex front engined car can get more than 50% drive to the rear is if the front axle drive shafts are removed as the rear differential's drive shaft is driven by the front differential.
Who is correct?
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Dave,
The question about torque ratio is a common one. I will try to answer it as well as I can.
Lets begin by examining a common cause of confusion: If the front and rear axles were to be locked together completely, what would the torque ratio be? Well, many car magazines would write 50/50 in such as situation, which is completely wrong. The only thing that one can be sure of in such a situation is that the front and rear axles rotate with exactly the same speed. The torque ratio will then depend on things like turning radius, vehicle speed, tyre rolling radius, vehicle weight distribution and of course the surface of the road.
If the car turns and the speed is low (approx < 40 kph) the front wheels will want to move in a circle that is outside the rear wheels. That means that they will want to rotate faster, which means that additional torque will be transferred to the rear wheels until the drive slip of the tyres compensate for the difference in circle diameter. If the axles are locked, the front wheels will actually brake and the rear wheels will drive the car.
Similar things happen if the rolling radius of the tyres front and rear differ. That can be due to using different dimensions (should be avoided!), different brands, differently worn tyres etc, but also because of different loading of the vehicle (different weight distribution). A smaller tyre rolling radius on the front than the rear will cause more torque to be transferred to the rear.
If the ground surface differs between the axles, the torque ratio will of course also be affected. If the front wheels are on ice and the rear ones are on tarmac, the torque split will be almost 100% to the rear. The corresponding is true the other way around.
So much for a car where the front and rear axles are completely locked together. But why did I spend so much text explaining that? Because the Haldex coupling Gen II is capable of distributing the torque between complete front wheel drive and (almost) a complete lock between the axles. That means that the Haldex Gen II can transfer more than 50% to the rear if the surface differs front/rear, if the car turns slowly, if the car turns very hard while running at speed (that will tend to lift the inner front wheel -> more torque can be transfered to the rear), if hard acceleration causes a change of the weight distribution backwards etc... It can however not do so in any arbitrary situation.
Note that everything above describes what is possible to transfer, not what is actually transferred! The latter depends on the control algorithms used which try to continuously optimize the car behaviour while you are driving. When you are accelerating hard, as much torque as possible will be transferred to the rear in order to optimize traction. When cruising the highway much less torque is transferred in order to optimize things like fuel consumption. When taking a corner the torque transfer will depend on a number of things that are all aimed at making the car handle as well as possible. The target behaviour is defined by the car manufacturer and may differ somewhat between different manufacturers.
I hope this helps and that I didn't confuse you to much!
Please note that this answer is given as a private person.
Best Regards
Staffan
Well instead of insulting me, try and answer my sepcific concern! 
In one of the many shots fired from your fact gun, you aimed an insult bullet directly at me, claiming I believe in fairy tales…
Please quote me correctly. I merely ASKED who had provided such info, to your very specific claim of 70% going to the rear.
And if you did feel that I made a "personal attack", then I apologise, as it wasn't meant to be "personal" at all. 
As an owner, who’s driven thirteen thousand miles in an R32 and had the Haldex controller fitted...
And I am speaking as a highly qualifed Automobile Engineering Technician, who fully understands the detailed operation of transmissions, and particularly four wheel drive transmissions, and has spent many, many years working on such systems.
And I add to that my own personal experiences of driving various Haldex cars - albeit with just the "standard" Haldex software in the controller.
I can confirm that if I put it in Race mode and perform a standing start, there is an unquestionable sensation of being pushed down the road rather than pulled. It sometimes feels like the fronts are doing nothing at all.
I don't question that at all, and I fully understand and agree with you. And it is simply down to weght transfer during acceleration which creates such an effect.
I understand the car is not permanent 70/30 RWD bias but if you really think that it can’t shift more than 50% to the rear wheels then you sir, have never driven a MkV R32 in Race mode.
But I am sorry, I have to disagree with you. Please tell me how the Haldex unit is able to disengage the drive to the front axle? It can NOT do so, because the front axle is permanently driven, irrespective of what the Haldex is doing. The Haldex is simply a clutch, and not a differential, and so it can NOT dynamically apportion torque from one axle to another. At best, irrespective of weather the Haldex is standard or "race", the Haldex unit simply locks its clutch at a clamping force of 100% - and this simply locks the rear axle to the front - meaning an exact 50:50 bias.
With your "Race" mode, what is actually happening, is that the Haldex is locking its clutch before you move off, thereby giving and exact 50:50 bias, but, because of the weight transfer effectively being pushed to the rear of the car during acceleration, it then "feels" like the fronts are doing very little, and the rears feel as though they are doing the major share of the traction. The actual apportioning of drive though can be no more than 50% to the rear axle.
I would take my own experiences and manufacturer info over a bloke on a public forum, no offence.
Firstly, no one is doubting your "experiences". However, what you "feel" through the seat of your pants is not the same as the fundamental priciples of Automobile Engineering.
Furthermore, Haldex Traction have repeatedly been found to "fudge" their figures, and squew their claims. Haldex make incorrect claims by ignoring the "industry standard" of describing vehicle dynamics. Google "Vehicle Dynamics International", blag yourself some free tickets, and then speak to some of THE most eminent professionals of the motor industry - and not one will back up Haldex Tractions' methods of describing the distribution of drive in their four wheel drive systems (or the way Haldex "discredit" 4wd systems with an ATB centre differential).
Kind regards.
