Thread: What does extreme articulation do?

the little bit of traction the wheel on the downside offers can be just enough in some circumstances, the other thing it does (on a beam axle) is allow the uphill wheel to tilt over and grab at the ground better as its got a "squarer" contact patch.

more later if thats not enough.

Originally Posted by Blknight.aus

the little bit of traction the wheel on the downside offers can be just enough in some circumstances, the other thing it does (on a beam axle) is allow the uphill wheel to tilt over and grab at the ground better as its got a "squarer" contact patch.

more later if thats not enough.

It does nothing but look good....

You are right in that it offers little to no traction advantage, and if you want a larger contact patch then drop pressures so you tyre can flex.

It does however make the vehical more unstable on side slopes but like I said it looks impressive.

Originally Posted by Blknight.aus

the little bit of traction the wheel on the downside offers can be just enough in some circumstances, the other thing it does (on a beam axle) is allow the uphill wheel to tilt over and grab at the ground better as its got a "squarer" contact patch.

more later if thats not enough.

Not enough, Dave

1) The total amount of force holding up the vehicle will equal its weight. So any weight on the downhill wheel is taken from the uphill wheel. The contact patch of the uphill wheel is consequently reduced, so unless the downhill wheel is over a stickier bit of ground, the traction gain would be pretty much nil.

2) The angle of the upper wheel and the "squareness" of the patch sounds like a bit of a phurphy too, because that depends on the angle of the ground, which is likely to differ depending on ruts etc. Just look at the classic "cross-axle" stuations - the ground is rarely equally anged at each wheel. Especially with reduced air pressure, the contact patch will work fine off to the side of the tyre, and this is why off-road dedicated tyres have tread there. It's also one reason why crossplies are still preferred for dedicated off-road tyres.

Now, I'm not saying I'm right, just presenting the counter arguements.

It will keep the vehicle more level over wombat holes etc as it will let the suspension work/walk rather than pull the body with it. The down side is more lean on side slopes.

Also, it is often easier to lift a wheel over an obstical than try and drive a wheel up it. I have learnt this with r/c rock crawlers. I have dialed out most of the travel from my suspension on my r/c crawler as it has locked diffs and it is more capable if it lifts a wheel than if it keeps them on the ground. And trust me, I can change it from almost no travel to having two wheels on a wall and two on the ground side on.

it's surprising how much traction can be garnered from unsprung weight alone. The weight of a Salisbury assembly shouldn't be sneezed at, although I don't like the lack 'control' from unrestrained springs, although some other form of mechanical restraint, e.g. limit straps could be utilized effectively after a spring dislocates.

I've only very very briefly tested this on the jacks and so wont have the experience that many others that drive dislocated will.

I'm not a believer in dislocating springs, irrespective of the illegalities, because it doen't allow the suspension to work and it seemed to me to throw out the natural balance of the articulation.

I've got (had!) a Series ute that was brought out to 100", coiled at the rear and sprung over at the front. The back had nothing on it and was running the lightest OE coils I had.

I stuck a table jack under 1 wheel and lifted up to about probablt 30cm off the ground before the spring dislocated. The front suspension barely twisted and the rear of the Landy pretty much just lifted. Sorry, no pics.

When I retained the dislocating spring everything then started to work as it should have:

This is playing with my brain

The weight keeping the lower wheel down won't just be the weight of the axle, it will also be some of the weight of the vehicle, transferred from the spring on the opposite side - since the spring is inboard of the wheel.

But ignoring all that for the moment, see the diagram below. Whatever the situation, and for any given spring length and rate, there are three options once you reach 0 preload through spring extension: the suspension travel is limited (by straps, shock absorbers or whatever) to that length, or the axle can drop and the spring is allowed to dislocate, or the axle can drag the spring into negative proload (so the spring is in extension and trying to pull the wheel up).

If the ground is, say, 50mm beyond the reach of the standard spring droop, having a further 50mm of droop will get your wheel on the ground (a la Slunnie's pictures) but will it do you any good there? (as Maggot 4x4's R/C example suggests it won't.)

If your wheel can't reach, you have 0 kg on the ground (made up for at the other 3 wheels on the ground). If you dislocate, you have the weight of 1/2 the axle plus one wheel, plus transfer of some weight from the spring on the other side. If you retain the spring you have the above, less the preload on the spring (or plus the negative proload for the pedants).

With something like 1 tonne each through 2 wheels and perhaps 100kg through the other 2, surely it's the lockers keeping traction. And surely keeping all wheels on the ground in that situation is just cosmetic at best or (thanks Maggot4x4) possibly even detrimental?

articulation also comes into its own in situations where your crossed up, bad karma for side sloping but in the case where you have the LF and RR in holes thats where it shines...

But theres a limit, too much of a good thing and all that, as to how much is useful and much beyond that point your just frigging with suspension geometry and the like...

The last thing that IMHO makes all the articulation you can get a good thing is FEEL. A wheel touching the ground will talk to you, one hanging in mid air doesnt tell you much untill it hits something. The wheel doesnt have to offer much in terms of drive but that little bit of extra lateral traction and feed back is always a good thing in my book. (naturally I dont mean to the point where the axle has swung through 90 degrees and is perpendicular to the chassis.)