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knot board said.. Hi HappyG,
Even the best 'real' 4x4's still are only effectively 2x4 unless they have diff locks installed front and rear.



Only rarely will a 4X4 be only as effective as a 2wd.
The diff equalises the torque to each of its 2 output shafts.
en.wikipedia.org/wiki/Differential(mechanical_device)
If both front wheels are on ice but the back wheels on bitumen, no torque goes to the back axle of a 3 diff 4wd. The rwd 2wd wins for a metre or two.
If both left wheels are in ice and the right wheels on bitumen no torque goes to the right wheels. Both 4wd and 2wd have no traction.
If all wheels have about 1/4 unit of traction in even, slippery mud, the 4wd has 1 unit of traction and goes, the 2wd only has half a unit and doesn't go.
A diagonal crossing where 2 diagonal wheels lose traction is OK in a 4wd with front and rear diff locks, but in this case just a centre diff lock is no help.
A 2wd with a locking diff should outperform a 4wd with no diff locks in such a diagonal unweighting case.
Diff locks or limited slip diffs avoid these scenarios by not being limited by the weakest link.
Diffs locks aren't really necessary these days, they'll soon be completely phased out. With computerised ABS the spinning wheel(s) can be individually braked sending torque to the best axle or wheel. Not quite as efficient energy wise to do it this way when traction is varying all over the place, but a lot simpler if you've got all the ABS sensors there anyway.
The Falcon RTV ute had a locking back axle and could famously embarrass 4wds with open diffs. It's about all you need really, plenty of ground clearance. Cheap to run, where else do you want to go? Pity they dropped them from the line up. The Territory 2wd has a similar system. We mistakenly rented a 2wd Territory for work once in sandy country. It was fine. Do you reckon I could tell the non-mechanically minded to crawl underneath and convince themselves it was only 2wd.