Does 4WD work in reverse?

[dave_aber]

Not even the King of off-roading can cope with an ice rink.

What a lot of 4WD pilots seem to forget that is in a lot of poor conditions, their 4WD will get their car moving when a 2WD will be stuck. However, once moving they will have to stop it again. For that they will use their 4-wheel brakes. We all have 4-wheel brakes. (Unless you are out in an Austin 7!). If you struggled to get going on a slippery surface, then you will struggle to stop as well. So (apart from the skilful and gentle use of 4WD engine braking - a sadly dying skill) the 4WD and 2WD vehicle will both have the same issues stopping.

Add to that the fact that the 'typical' 4WD (Land rover / Land cruiser, etc) is big and heavy, it will be more difficult to stop than a light hatchback.

Doesn't help us in Bongos really, being almost as heavy as a range rover!

Momentum is the key. Preserve it to keep going - but have too much and you won't stop / change direction when you want to.

[andyfb78]

Just a note on the reversing versus forward 4wd workings...
I feel a ramble coming on but bear with me...

Going forward up a hill there is more weight on the rear tyres, the effective centre of gravity at the road has shifted rearwards. Going down hill the opposite is true, weight is effectively shifted forwards.

So a front wheel drive car will go in reverse up a hill more easily than it will go forwards up a hill, and a rear wheel drive car the opposite....
Subtle maybe, but when balancing the grip to torque in slippery conditions this has a noticeable effect.

So with regards the bongo, it effectively works a a rear wheel drive system UNTIL the rear wheels slip, whereupon the viscous coupling sees a speed difference and transfers some torque to the front wheels. This means some wheel spin will occur before the bongo becomes 4wd.

So going uphill forwards there is more possibility of inducing a 4 wheel spin (rear have already lost grip, and the fronts which have less grip due to less weight transfer, have to do all the work) once a wheel is spinning on ice it does nothing useful, and the only way to recover is to back off and try again (this is what the electronic traction control systems attempt to do for you).

In reverse the opposite is true and when the rears spin, the fronts which have better grip assist, reduce the torque available to the rears and give more chance of climbing the hill.

This assuems of course that the effect of the different gear ratios is negated by careful application of throttle to avoid the inital loss of traction...... driving in slippery conditions is all abotu careful application of throttle, and backing off as soon a slip occurs...(too much time testing landrovers I'm afraid)

I'm not sure about gear ratios forward to reverse in the bongo, never checked, but if reverse is lower than first (quite possible in an auto) then it will more easily provide too much torque to cause wheel spin, so this might have more of an effect.....

Phew.....

landrovers, when diff lock is applied are true 4wd, so all wheels, or more accurately both axles, are powered at the same speed. with the diff lock not applied, they are actually less effective than our bongos' system as all the power can be lost through a slipping axle.