I was watching an interesting episode of XOverland about 4x4 driving and was left a bit confused when Andrew White claimed that permanent 4 wheel drive vehicles by default are not true 4 wheel drive. He used a Defender stuck on a small bolder as a demonstration. The trucks front tire was spinning while the back tires were pretty much doing nothing, consequently the truck could not progress over the bolder. Only after engaging the center differential locker did all the wheels begin to move and finally the truck overcame the obstacle. Andrew stated that until the CDL is engaged your truck is technically 2 wheel drive. I understand his argument I think but as I also know that Land Rover briefly discontinued the fitment of the CDL to Discovery 2 models because they felt that the electronic traction control would be sufficient. So if what Andrew is saying is true than that wouldn't that mean that trucks without the CDL are 2 wheel drive? Despite being classified as an AWD vehicle?

What about AWD sedans and wagons like Audi, Volvo and Subaru? I dont believe that they have any differential lockers and yet they participate in off-road rallies.

I would even ask how than should a Discovery 2 model with the CDL be operated during winter driving? Should the CDL be engaged anytime the truck is expected to drive over wet/slippery pavement in order to take advantage of the "true 4x4". The manual does say not to drive in speeds of over 40MPH with the CDL engaged.

Heres the video link:

 

CDL unlocked, our trucks are AWD with open differentials front, rear, and center. Meaning that all available tq will go to the wheel with the least amount of available traction, and all that entails.

Traction control aims to mitigate that by braking that wheel with the least amount of traction, redirecting the torque to the wheels with available traction to move forward.

AWD passenger vehicles from Ford, Volvo, Subaru, Mitsubishi, etc. use TC to some degree, much the same way the disco does, with most of them having a center differential that allows limited slip by way of a viscous coupling, or electronically controlled clutches.

To answer your question about winter driving, working TC should be more than enough for all but the deepest snow. If you're in really deep snow (or you need to parallel park on a 3' snow mound), then a locked CDL is the way to go.

 

x1 agreed

 

Ian Ashcroft, who knows a bit about Land Rover gearboxes, recommends CDL locked if you're driving constantly on surfaces where you have slippage between the front and rear propshafts.
His experience is that not locking it causes a high speed differential between the center diff front and rear outputs and will grenade the center diff sooner.

 

Agreed with the above said... but Subaru now has the edge with Symmetrical AWD .. and its quite amazing ..