this was posted on a non car related forum that I sometimes frequent. I can't say I'm vastly technically minded but just thought the broad sweeping statements paint the Fatty etc in a poor light and wondered if there was any way to refute or ameliorate such generalisms?

Quote:

Most people that own 4WD vehicles know nothing about them. When turning a corner the front wheels follow a different path to the rear wheels. In order to allow for the different pace of travel the drive to the from and rear axles is routed through a central differential. The differential lock on most 4WD vehicles locks this central diff. If you fail to do so you are in effect only 2WD. If you lock the central differential whilst on a very hard surface such as tarmac the axles will fight one another. On most pretend off roaders or snow cars like the Golf 4WD the whole thing is electric and uses the ABS system to achieve traction by braking the spinning wheel. this makes up for the fact the idiot driving knows nothing about 4WD. It is very effective. Perhaps sufficiently effective that the old fashioned axle system and central transfer box has had its day. Land Rover (arguably one of the best off roaders ever) have abandoned the old axle and transfer box system in favour of driveshaft and electrics for all of their vehicles other than the Defender, the one that people who actually go off road buy. The W market offerings, Disco, RR etc. are driveshaft. A quick look at most of them will show you they are unsuitable for off road use, many even have the spare wheel underslung where it will be deep in when you need it...

The diff lock therefore on 99% of 4WD road vehicles locks only the central diff. As an additional option it is possible to lock the rear axle diff as one would on an agricultural tractor. This locks both the back wheels and is very useful in deep mud or very bad traction conditions. I doubt you would ever need this facility on a snowy road. The diff lock must be turned off before turning a corner or the locked axle will fight the steering wheels.

The Golf 4WD and similar are in fact therefore much better than the old two axle type vehicles like the Pajaro/Shogun, old Disco etc. The electric sensor will stop whichever wheel is spinning irrelevant of its position on the vehicle. These types of vehicle are popular in snowy countries like Switzerland and in Luxembourg, where we used to live. Fitted with the right tyres they will cope with very deep snow, within the limits of the vehicle's ground clearance. Only at that point is there any advantage to the higher ground clearance of off road type SUVs. For the bigger SUVs (Pajero/Disco etc) the extra weight is more of a handicap than the little extra ground clearance - certainly when it comes to stopping I would rather be in the Golf than the Pajero.

He is not wrong, as such. The bit he's missing is that the traction control on our cars does the same thing as his electric bits.

I believe our centre diff locks automatically so we don't even have to hit a switch for that. On the later cars, the diff is electrically locked, so can vary and be much smoother in operation.

Due to the effectively open rear diff we have, we don't have to worry about transmission wind up.

On cars with a viscous centre diff, there is enough slip not to have wind up when cornering, but will progressively lock as the different output shafts turn at an increasingly differing speed.

That's my understanding of it, from memory.

Of course with a 4wd vehicle, you'd argue that there is only 25% of the torque going to each wheel, on a 50/50 split system, as oppose to a 2wd car, which would have 50%, so it's less likely to wheel spin in the first place.

With modern day traction control on our cars, the wheel with the most grip should always get the most torque.

Will do a bit of reading up...... 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

Last edited by mjdronfield on 15th Feb 2014 4:59pm. Edited 1 time in total

On my 2007 TDV8 , ECM controls the Haldex, which in turn transfers drive to the rear axle, so when he says its a Front wheel drive most of time, he's about right.

I had to replace the Haldex motor last year,...£500 at main stealers  GONE 2010 Facelifted 3.6 TDV8 - Stornoway Grey + 22" Overfinch Olympus
HAVE 1999 Discovery 2 GS 4.0 V8 - Silver - Off Road Toy
GONE 2013 L405 4.4 SDV8 Vogue. Black with Silver roofline and 22" s
HAVE 2015 Jaguar XF.

Just had a quick double check, the L322 had a Torsen centre diff, which would normally give a 50/50 torque split. It would allow up to 2:1 split as wheel spin occurs, so upto 66% could go to the front or rear end with the most grip, so the end with a spinning wheel would still get at least 34% of the torque.

The axles are open at both ends, so there is no locking rear diff. The system relies on the abs sensors and traction control to brake the spinning wheel and ths push torque to the wheels with grip.

The later cars had an electronically operated centre diff, which allowed for more accurate and smoother changes in the torque split.

In the changeover, for a while, the diesel kept the Torsen centre diff and the petrol had the electronic unit. When the td6 was dropped, the Torsen diff disappeared.

 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

I think the first sentence of the quote is pretty accurate, and it also covers the person who wrote it, 56 TDV8 Vogue SE
9 Freelanders, 2x 2002 TD4ES, 2001 TD4, 2002 1.8GS, 2000 XEDI, 2x 2000 1.8ES, 2004 1.8 & 2000 1.8 GS (rolled)
91 Lotus Carlton (sold)
90 Lotus Elan (BRG)

Varies by vehicle - so only a fool would make such sweeping generalisations.

I have a Jeep Wrangler - that is true 2WD most of the time - the centre diff is open or locked - when you engage 4WD it locks the centre diff - so it can only be used on a loose surface - I also have front and rear locking diffs but they are not standard.

Some other cars have a true diff in the centre that gives permanent 4WD - with varying front/rear splits

Newer cars have all sorts of variable diffs, traction control and abs combinations that can shift power between the 4 wheels in an active way.

I kind of get what he's trying to say, but it's not articulately helpful - I guess the point is that people should understand what they have, how it works and what it's limitations are.

I'm pretty sure of the limitations with mine - me.

I still think there is hardly any aftermarket off roading stuff for the L322. I know it's probably the least of the land rovers to be taken off road perhaps, but it's still a range rover.

If you had a classic or a P38 I dare say you could get air lockers and all sort of diffs and add ons. 2011 Range Rover Vogue SE 4.4 TDV8

Previous cars :
2003 Range Rover Vogue TD6
1999 Discovery Td5 ES
1995 BMW M5 3.8 6 speed
1992 Range Rover 3.9 Efi Vogue
1992 BMW M5 3.8
1988 BMW 735i SE
1989 Ford Sierra XR4x4 2.9i
1981 Ford Fiesta Supersport

With the l322 though, most of the capability that aftermarket locking diffs etc provide is somewhat already built in to the vehicle as standard via its torque biasing centre diff and it's traction control system. Features which weren't standard on earlier rr models. V8 or else ...