Anyone know owt about this...

Sliding things having less friction with the ground than rolling things?

Thinking of the forces which would cause the twist ?

Steve

Think how a crawler steers, older gearbox driven ones take the drive off the side you want to steer, then apply brakes to it. Now when you're going downhill the exact opposite to this occurs because the driving force is gravity and the engine is a braking force.

If one back wheel locks, and the picture shows one rolling backwards which suggests the other is rolling forwards at a faster rate, then there is a slewing force.

I knew a chap (barrister) conscripted in WW2 and taken prisoner in Libya when he was 40, who was being trained on a tank. He had been taught to declutch the lh track to turn left under power and right vice versa. However when he had climbed a hill and started down again the tank started veering to one side, to correct this he declutched the opposite side as he had been taught but didn't apply the brake, the whole plot turned over and he never drove a vehicle again.

The correct procedure is to apply opposite lock and accelerate hard but in low gears the extra speed to catch up won't be there because of the rev limit of the engine.

I've been caught out on grassy slopes with the 4wd tractor and despite training and experience the natural urge is to attempt to control and slow down.

AJH

Chubby Checker?

The forces effectively act from the center of gravity this is behind the front wheels and the small differences in force direction and in the friction of the front wheels will make the body pivot round one or other of the front wheels without (enough) friction for the rears to stop it.

Well that's my theory...

In this case, having half decent all terrain tyres on the front & fairly well worn sand tyres on the back won't have helped any. That's a *good* recipe for making the back overtake the front when you're going downhill, especially in mud. :-/

Has anyone got any figures on the weight distribution of an empty ambi? I'd have thought they're a bit front heavy on the flat, let alone when driving down a steep slope. I know pinz 4x4s and short wheelbase unimogs have a nasty habit of lifting the rear axle under braking or when driving down very steep inclines. In one of my youtube vids you can hear a chap talking about having quarter of a tonne of concrete in the back, he said that from the cab of a 101FC although it was a GS and not an ambi. He put it in to stop the rear from lifting so much and also to put more grip down at the rear as it was very light. You can just about see his 101 pulling a volvo c303 out in one of the vids.

The main reason for this was to prevent cross axle problems with the hard springing.

AJH

Sounds plausible, the 4x4 pinz rear suspension doesn't move much when it's unloaded, and even my Defender 110 truck cab doesn't articulate as well as it could do for the same reason. I do find the Defender rear steps out under hard braking though so I'd have thought the

101FCs would be a bit worse with the cab and driver up the front and higher up too.

It's a good recipe for the back wanting to overtake the front in many other circumstances as well.

On or around Fri, 1 Feb 2008 20:21:53 +0000, Ian Rawlings enlightened us thusly:

some bigger ones on their side here:

and more large action:

?v=mwYSwvmZq74

Wouldn't be allowed within Ken's LEZ!

Heh, nice. Although I'm more impressed that I can watch youtube videos jitter-free over my 3G "mobile broadband" connection from a shit hotel in London!

Tatras rule, although the big trucks do seem to have some problems with climbing slopes, probably something to do with shifting 12 tonnes or so of metal!

Here's something smaller, a Unimog doing what only they seem to be able to do;

And another, very short but very impressive;

The older mogs seem to be the best, I saw a modern mog at a trial recently and it was a bit shit, far too big and heavy.

On or around Mon, 4 Feb 2008 22:42:03 +0000, Ian Rawlings enlightened us thusly:

this looks like the same truck:

'ere, what about one of these?

interesting-looking suspension. De Dion axles on coil springs... Had that on the Rover P6.

looks rather good, make a nice camper conversion :-)

250bhp cummins engines...

Depends on the position of the COG

Heheheh, yup, that's very impressive, thanks. ;)

One of the loacl gritters is based on a Unimog, I wonder if it can do that?