As there are so many 4x4 systems out there in SUV's, Estate cars and some saloons, it would be interesting to know how effective they are.  There are a couple of videos on You Tube from the States suggesting through a demonstration on some rollers that the Subaru Symmetrical system outperforms all the other vehicle in the test.  It would be equally interesting to see how the Haldex 5 fitted Octavia Estate would have coped in the same situation.  One would have thought it would have been equally as good or Landrover woukld not be using it

John

The performance of the Haldex and especially its "electronic diff locks" is greatly dependent on the software that controls it and what characteristics the manufacturer has opted to emphasize.

 

This means there's a lot of variation on their functionality between brands and even models. That said, I'd love to see a test on how the system on the Octavia performs.

Subaru's AWD is 'symmetrical', such that all the drive shafts are the same length. Power will take the path of least resistance, so having a 'symmetrical drive train means there is no difference between drive to each wheel. Also, the poor 'part time' 4wd systems are let down by the inherent flaw that they all have, namely that as soon as the power is transferred to the rear axle, and the car moves forward, its instantaneously removed again. So the car is back where it started - stuck. 

See below at 7:00m. You see the car has grip (front right and rear left), but the car isn't moving anywhere as the haldex system can't transfer enough power from the spinning wheels to the wheels with grip. Subaru's AWD is just that - AWD, so if one wheel has grip the car will move forward.

 

 

 Also, the poor 'part time' 4wd systems are let down by the inherent flaw that they all have, namely that as soon as the power is transferred to the rear axle, and the car moves forward, its instantaneously removed again. So the car is back where it started - stuck. 

 

This really shows how important the programming is. The Haldex system would be perfectly capable of getting the car moving if only the electronic difflock system would be smart enough to keep breaking the slipping wheels even after the car lurches forward.

 

Subaru's AWD is 'symmetrical', such that all the drive shafts are the same length. Power will take the path of least resistance, so having a 'symmetrical drive train means there is no difference between drive to each wheel. Also, the poor 'part time' 4wd systems are let down by the inherent flaw that they all have, namely that as soon as the power is transferred to the rear axle, and the car moves forward, its instantaneously removed again. So the car is back where it started - stuck. 

See below at 7:00m. You see the car has grip (front right and rear left), but the car isn't moving anywhere as the haldex system can't transfer enough power from the spinning wheels to the wheels with grip. Subaru's AWD is just that - AWD, so if one wheel has grip the car will move forward.

 

 

Subaru describe their system as Symmetrical AWD not only because the drive shafts are the same length due to the engine being mounted longitudinally, but because the AWD system maintains a near 50/50 split (the one in mine is 60/40) and there is no mucking about waiting for wheels to lose grip. This is partly why they perform well vs other systems in similar vehicles. It is also why they drink so much fuel. But you don't get the loss of power as soon as it is moving, as the system maintains the symmetry rather than trying to become a FWD/RWD again. The latest ones have also moved to EDLs on both axles rather than mechanical LSDs (though they still keep the middle one) as these systems are now as good. As above, it depends on the programming. I've seen my car doing a cross axle test and the wheels in the air were turning at the same speed as those in contact with the ground (with a little stutter, as you'd expect), rather than spinning uselessly.

I am suggesting to a couple of 4x4 magazines that they might consider something on the lines of the link below.  This particular test was in the USA in around 2008. A full length video of up to date vehicles would be of interest to many.

 

tps://www.youtube.com/watch?v=med9V-vO9d0

All very interesting, but not important in the real world.

 

I had a Haldex 3 pre-facelift Scout and now a Haldex 5 4x4. I have never (touch wood) got stuck in either and I have been far from the beaten track on occasion. Ability to assess the conditions is paramount, the best off roading 4x4s can get defeated in a wet grass field on the wrong day. Always have an exit plan (never stop at the bottom of a hill, etc).

 

I find the biggest limiting factor of where I'm prepared to go is ground clearance, not drivetrain concerns.

 

Sure he gets stuck in the vid above driving at a wet, muddy, steep, slope on summer tyres, but try the same on hard dry earth or with better mud tyres and the result could have been different (though he would have grounded the belly if he had made it.....). When was the last time you drove at a cliff in a car?

 

It's all compromise, but the Octavia can do more than you reasonably need and anything beyond that isn't really Estate Car territory, but it is a bonus that the car can do it.

 

Niall

All very interesting, but not important in the real world.

 

I had a Haldex 3 pre-facelift Scout and now a Haldex 5 4x4. I have never (touch wood) got stuck in either and I have been far from the beaten track on occasion. Ability to assess the conditions is paramount, the best off roading 4x4s can get defeated in a wet grass field on the wrong day. Always have an exit plan (never stop at the bottom of a hill, etc).

 

I find the biggest limiting factor of where I'm prepared to go is ground clearance, not drivetrain concerns.

 

Sure he gets stuck in the vid above driving at a wet, muddy, steep, slope on summer tyres, but try the same on hard dry earth or with better mud tyres and the result could have been different (though he would have grounded the belly if he had made it.....). When was the last time you drove at a cliff in a car?

 

It's all compromise, but the Octavia can do more than you reasonably need and anything beyond that isn't really Estate Car territory, but it is a bonus that the car can do it.

 

Niall

 

Agree with most of it. Most of the time it'll be perfectly capable.

 

Ultimately though the best AWD systems make the most of the grip thats available. The car shouldn't get stuck unless all 4 wheels are spinning through lack of grip. In the video only two wheels are spinning so the car isn't making the best use of the available grip. I've seen a '4wd' car stuck when 3 wheels were in the snow, and one wheel was on the ploughed and gritted tarmac. It wouldn't move as it couldn't transfer enough power to the wheel with grip. If you then imagine this happening all the time when for example climbing a sloppy hill, the best systems constantly shuffle power the the wheels with most grip.

Niall, I'm going to agree with everything you said, except Haldex 3 was never fitted to any Skoda, as it was a Landrover specific version.

Ive managed to beach my Octavia 4x4 on a snow bank and that was the only time it got stuck. I've also aborted one journey down an unmaintained road due to seeing I clearly didn't have enough clearance, so now I have something with a reasonable 220mm

Niall, I'm going to agree with everything you said, except Haldex 3 was never fitted to any Skoda, as it was a Landrover specific version.

My bad, can't remember all the specs of a car I no longer own!!