Various 4 WD Systems

[Max_99]

So we hear that 'proper' Audi's ( N/S engine ones anyway) have the Torsen 4 WD system, most current VW's and Skoda's have the Haldex system, and Subaru have a viscous coupling? That right?

And in terms of actual 4 WD performance which are 'best'? As far as I understand it the Torsen are genuine fulltime 4 WD, while the Haldex systems are typically front WD till something slips then the rear wheels kick in, and Subaru claim their system provides drive to all 4 wheels all the time? Doe sthat make the Subaru's 'better' than the Haldex system?

My interest is in establsihing the 4 WD capability of say the Superb/Octavia 4 WD's and new Passat 4Motion against the Subaru Legacy/Outback....so which is the real deal?

Thanks in anticipation.

[snow_muncher]

Subaru have a variety of 4WD systems, all based around a central diff + viscous coupling unit. The system is symetrical meaning drive shafts etc all all equal length.

Audi's old Quattro system does use a Torsen diff, basically an older and more expensive to manufacture design than Subaru's.

Both system are 'dumb' permanent all-wheel drive systems, with limited ability to compensate for wheel slip between the front and rear axles.

The Haldex system is an radical re-thinking of the all-wheel drive system, incorporating the best features of previous systems.

In its simplest for, Haldex is a computer controlled viscous coupling unit which emulates the best features of both visous coupling and torsen characteristics

The system actively compensates for wheel slip between front and rear axles, and it does this much faster than the drivers of mechanical 4x4 systems can.

Haldex also has a few other tricks up its sleeve, most noticably disengagement of power to the rear axle under braking. This elminates the risk of 'torsen oversteer' when braking during corning.

In terms of the difference out on the road - Haldex is safer - you can put someone with no 4x4 or snow driving experience in a haldex equipped vehicle, and they will be able to drive about happy without slipping or sliding, without changing the way they apply power or brake.

If you want proof of how good haldex is, watch one of recent 5-gear episodes were Tiff is driving a Lambo round a snow/ice track (Yes, Lambo have Haldex in them, along with Audi R8's)

Its Audi plan by the way to drop the older Torsen system is favour of the haldex system, across the entire range.

The older 'dumb' 4x4 system require much more driver input, and can kick you up the backside if you don't know what to do

[2slo]

Well explained above. To which I would just add, the haldex system also has the benefit of being more fuel efficient than a comparable 4wd. Typically, if an AWD car were on a road in good conditions then 2 powered wheels are adequate and the haldex, sensing no slip, will not transmit power to all 4 wheels. With permanent 4wd the car doesn't have this option. Subaru make/ made some fine vehicles but the permanent 4wd versions in Imprezas, legacys etc have never been renowned for good fuel consumption.

[Llanigraham]

Haldex is also now used by Land Rover in the Freelander and Evoque, and is being looked at in others in their range.

[Max_99]

Subaru have a variety of 4WD systems, all based around a central diff + viscous coupling unit. The system is symetrical meaning drive shafts etc all all equal length.

Audi's old Quattro system does use a Torsen diff, basically an older and more expensive to manufacture design than Subaru's.

Both system are 'dumb' permanent all-wheel drive systems, with limited ability to compensate for wheel slip between the front and rear axles.

The Haldex system is an radical re-thinking of the all-wheel drive system, incorporating the best features of previous systems.

In its simplest for, Haldex is a computer controlled viscous coupling unit which emulates the best features of both visous coupling and torsen characteristics

The system actively compensates for wheel slip between front and rear axles, and it does this much faster than the drivers of mechanical 4x4 systems can.

Haldex also has a few other tricks up its sleeve, most noticably disengagement of power to the rear axle under braking. This elminates the risk of 'torsen oversteer' when braking during corning.

In terms of the difference out on the road - Haldex is safer - you can put someone with no 4x4 or snow driving experience in a haldex equipped vehicle, and they will be able to drive about happy without slipping or sliding, without changing the way they apply power or brake.

If you want proof of how good haldex is, watch one of recent 5-gear episodes were Tiff is driving a Lambo round a snow/ice track (Yes, Lambo have Haldex in them, along with Audi R8's)

Its Audi plan by the way to drop the older Torsen system is favour of the haldex system, across the entire range.

The older 'dumb' 4x4 system require much more driver input, and can kick you up the backside if you don't know what to do

OK....thanks for that. So long story short:

• What system would more capably climb a muddy slippery track? A Haldex or the Subaru version?
  
• And ditto above, but descending the same track?
  
• And wouldn't the Subaru be less likely to say skid on a sealed road in the first place as its already 4 WD?
  

Cheers

Edited 7 August, 2011 by Max_99

[snow_muncher]

• What system would more capably climb a muddy slippery track? A Haldex or the Subaru version?
  • The one with the best tyres tbh
  • Haldex
    

  [*]And ditto above, but descending the same track?

  • as above

  [*]And wouldn't the Subaru be less likely to say skid on a sealed road in the first place as its already 4 WD?

  • Not that simple tbh there are situations where the power to the rear can create the breakaway in the first place ( the torsen oversteer I mentioned for example )

I've driven both in mud snow and ice in the Alps, Devon, N.Wales, etc, etc - imho haldex wins hands down

The scooby does have a well designed underside though - well protected from grounding. VAG on the other hand, are naff for underbody protection

[Max_99]

• What system would more capably climb a muddy slippery track? A Haldex or the Subaru version?
  • The one with the best tyres tbh
  • Haldex
    

  [*]And ditto above, but descending the same track?

  • as above

  [*]And wouldn't the Subaru be less likely to say skid on a sealed road in the first place as its already 4 WD?

  • Not that simple tbh there are situations where the power to the rear can create the breakaway in the first place ( the torsen oversteer I mentioned for example )

I've driven both in mud snow and ice in the Alps, Devon, N.Wales, etc, etc - imho haldex wins hands down

The scooby does have a well designed underside though - well protected from grounding. VAG on the other hand, are naff for underbody protection

Thanks.....I had been holding my breath for the rumoured Superb Scout but I now hear that that is all it is.....rumour...but latest chatter down here is that a Passat Cross ( maybe badged an AllTrack??) will be revealed at Frankfurt for 2012 release??