Suspension Specific Bunfight Thread.

[Daan]

I think most would agree that in principle independant suspension is a more superior design in terms of allowing each wheel to cope independantly with its own requirements for suspension travel - its just it doesnt work reliably in off road in extreme conditions.

I would have thought that fundamentally the problem with any independant set up is how well it withstands rocks and snags.

With a live axle tube there is virtually no snagging risk and in the event of grounding out on rocks providing the casing is strong enough to take the weight/impact there shouldnt be a problem.

Once you start getting into link arms or wishbones below the drive shafts then i would be wary of rock climbing.

I dont agree with this: you only need to take a look at the american baja racers to see how they go over very rocky areas at 100 mph+.

Its just that with max articulation the independant sytem lets you down. Here you really have an advantage to have a dependant setup, so if the lh wheel goes up, the rh wheel naturally goes down.

daan

[LR90]

Forget diffs, springs and dampers. What you need is this!

Now that is different. Would make trips to Tesco a lot of fun

[Astro_Al]

Right. Thanks again for everyone's thoughts.

Its difficult, everything is a compromise. This thing is supposed to be an all-rounder to a certain extent, so its never going to excel at any one thing.

I'm offsetting the typical indy clearance issues (one wheel raises and the chassis hits the rock) to some extent by running portals. One of the 'normal conditions' advantages of indy is that there is more clearance underneath than solid axle, so its actually less likely to hit something. Add portal clearance to that, and you're going to have to find yourself in pretty hot water to come into clearance issues. Apart from Night Train's 'leg-wheels', you're not going to get much more clearance than that. Joining the links to the portal as high as possible will help too.

Even with an indy car, you don't get zero chassis deflection when one wheel raises - Mr Hooke and his law of boingy things says that the force on the suspension mount will increase as the spring is compressed, so there will be 'lift'.

Issues as I see it are:

1. Side slope stability.

2. Possible body roll on corners (not unique to indy of course, just difficult to counter while including flex).

3. Under extreme circumstances, not lifting the lowest point (chassis) over an obstacle.

Mr Milemarker: come now - even Fridge has managed to refrain!

Fridge, I didn't really think of the Frog etc as I'd like to keep it 'different' and vaguely experimental. They've done their swing arm jobber, and done it well. I don't want to reinvent the wheel (though a copy of that would no doubt rock compared to the clusterfawk I'm about to brainfart). Something more along the lines of 'the other one', savvy? Plus I don't want to have to unscrew my legs to get in...

Daan - you have a Yellow card for post 22.

Muddy, yeah the travel is cool, but the forces are higher and the heat not insignificant. Articulation here will be limited by acceptable joint angle on the driveshafts between 3rd member (diff) and portal box. Meh... I want to try something different, 4-linked beams are everywhere.

Pete. Thanks, thats a nice project. Except I hate it, of course... Nice to see something different.

SteveRK, with clearance like I'm talking about here (this isn't a remodelled Freelander - we're talking 40+ inch tyres, portal clearance plus high angle drivelines, there will be significant daylight under the chassis), I don't see normal 'snagging' as a problem. One aim is to have a completely flat underside. This can be done because the diffs are integrated inside that belly pan, not like beam axles where the axle case is FAR more likely to snag IMHO. I appreciate your thoughts though. Watching rockcrawling, there is a great deal of axle / chassis member snagging with 'regular trucks'. [And no, if I were building a balls-out rockcrawler there's no way it'd be indy].

I agree partially in that it is a weakness of indy generally, which is why I'm looking into forced articulation or some kind of passive suspension geometry input, either to raise over an obstacle or to cope with roll forces on a side slope.

I don't see the need to have arms/wishbones much below the level of the underside of the driveshaft - probably no worse than a regular portal axle at the outer ends, and progressively better towards the centre.

My mind is sort of envisaging pivoted balance bars between the shock top mount points. Its all a bit cloudy so far. I have some thoughts, but I need to find a 5 year old to show me how to use my crayons properly.

Thanks all. Keep it coming! Cheers, Al.

[FridgeFreezer]

This is probably a really bad idea, but... Regarding clearance, since your arms don't do anything but hold things on (unlike a live axle which contains driveshafts) why not make the driveshaft the lowest point and attach all the other links so they almost come down onto the top of the portal box. Bendy driveshafts are difficult but curved/arched links sound doable.

[Astro_Al]

John - i hear you. I was basically planning to put the lowest links/arms level with the driveshaft, so that a plate on the underside would cover it from direct loads/damage.

But yeah, essentially I agree.

Al.

[Daan]

Daan - you have a Yellow card for post 22.

?I never understood much of football. So explain?

Daan

[FridgeFreezer]

?I never understood much of football. So explain?

It means it's your turn to serve towards the wicket end of the table I think

[T1G UP]

I'm going in for the kill boys

well it's taken portal pete's dad 4 years so.............

[Astro_Al]

Oi!

Anyway, 4 years is nothing!

Don't worry Daan, neither did I.

Al

[FridgeFreezer]

Veering dangerously back towards "on topic", I'm not entirely sure I see the point of sticking a portal end on an indy setup, the bit that usually gets you stuck with a live axle is the diff pumpkin digging in or the axle tube dragging along the ground. Now, with indy you've already raised that up, and the links to the hub can be made so they're not much lower than the driveshaft, if at all, and normally pointing diagonally down rather than a flat profile.

The thing that snags indy setups off-road is the lack of a link between the wheels, if you're looking at forced articulation anyway you've overcome that problem.

It just seems to me that using a portal end opens you up to some new forces you don't normally get when the centreline of the wheel is between the upper & lower links - a bit like you get axle wrap on a live axle. The portal box will be giving leverage, both trying to rotate and also tuck under / out when the wheel hits something or is put under load. It's noticeable that the Pinz hubs have their own sort of torque-tube affair rather than being articulated at the hub to keep the wheels flat, perhaps that would give a stronger and simpler setup?

Edit to add: Which brings me back to "buy a pinz and modify it" which would seem much easier, all things considered.

[nicks90]

i take it you mean something like the attached carp ms paint effort?

if so, then in principle it has been done lots of times before - but i dont know about the portal drop box bits being attached, although that shouldnt make any difference as its basically still a 'hub' so the theory is still the same.

In quite a few of the home built baja buggies the links are actually attached to the diff frame (not unusual for them to butcher a nice strong dana axle)

so the diff is attached to the chassis and the links attached to the axle tube as close to the driveshaft output as possible. That way the drive shaft and links stay parallel and you dont need as big a slip joint in the shafts and keeps geometry simple.

[callum]

hummers use portals and independent supension dont they?

[disco_al]

Hydrostatic drive?

for this kind of thing, look at Merlot telehandlers, they are 4wd hydrostatic transmission, and on the larger versions they incorperate a levelling system to allow you to transverse a slope while keeping the body level......

just my 2p worth in an unknown field....

[FridgeFreezer]

hummers use portals and independent supension dont they?

IMHO That's more of a reduction hub what with there being stuff hanging below the centreline of the wheel, doesn't gain you much ground clearance although obviously reduces drivetrain load from the hubs backwards, and makes the driveshaft run a bit straighter.

[straight 6]

I know that it's going back a bit, but the Froggs were chain driven, with a reduction gear I think, then another chain to the hub's. The gearbox was off an Audi Quatro, and yes the rock crawing was a bit more of a problem for them.

[FridgeFreezer]

I know that it's going back a bit, but the Froggs were chain driven, with a reduction gear I think, then another chain to the hub's. The gearbox was off an Audi Quatro, and yes the rock crawing was a bit more of a problem for them.

Are you talking about the same Frogs we're talking about?

[jules]

Humor me

I've often though that you could simply take a Matsirati, Amarati or if your feeling rich a rivet (I don't have a clue what the correct spelling is) then all you would need to do is some minor chassis stiffening, Beef up the CV's and shafts and remove the hubs and fit portal hubs to it.

Its not that simple I know and don't have the common misconception, a racer is far stronger than any challenge truck

I could be wrong just a thought

[discojmz]

only other negative i can think of with indy suspension with particularly long arms to it (not that i really know much so its more of a question)

is

when wheels articulate downwards, do you not lose an appreciable amount of track width? moving in an arc, they come closer to the centre line surely?

like i say, i dont know, but im interested

jim

[Night Train]

only other negative i can think of with indy suspension with particularly long arms to it (not that i really know much so its more of a question)

is

when wheels articulate downwards, do you not lose an appreciable amount of track width? moving in an arc, they come closer to the centre line surely?

like i say, i dont know, but im interested

jim

You would if the suspension arms are equal length but if the upper arms are shorter then the lower arms then it has the effect of changing the camber of the wheel to keep the track at the ground contact patch almost the same. The overall geometry can be adjusted to minimise this.

[discojmz]

ah ok. thanks for that. i thought there must be some way around it but you never know until you ask

on a slight aside, in that case do lifted freelanders have narrower track width or suffer uneven tyre wear?

[Night Train]

ah ok. thanks for that. i thought there must be some way around it but you never know until you ask

on a slight aside, in that case do lifted freelanders have narrower track width or suffer uneven tyre wear?

What's a Freelander? I'm old school!

I don't know tbh, I've never been very interested in that end of the market. The last time I looked at light weight stuff it was Baja VW sand rails of the 70's, since then it has been LWB Land Rovers upwards (with the odd racing MGB thrown in).

[bill van snorkle]

I know that it's going back a bit, but the Froggs were chain driven, with a reduction gear I think, then another chain to the hub's. The gearbox was off an Audi Quatro, and yes the rock crawing was a bit more of a problem for them.

Whilst talking of the Frog, I've observed that it and many other Lagoda type vehicles are extremely short and high, which seems to suggest to me that there aren't too many steep offcambered hills in the event. True or false?

The IRS on Jaguars employ the axle driveshafts to also double as the upper control arms. Juggle things around a little and they can become the lower control arms for snag free ground clearance. I like Als idea of mounting the left and right coilovers to a pivoting crossbeam for crossaxle articulation. One could lock or provide variable resistance to the crossbeam pivot to tune higher speed on/off road handling. A front suspension I built some years ago when I wanted to make a 4WD VW Beetle was to bolt a diff and and front wheel drive stub axles onto the twin transverse torsion bar VW suspension assembly, and then centrally pivot the assembly off the chassis, located for and aft by an ''A'' frame.

I'd avoid the Pinzgauer type swing axle suspension at all costs. I've seen Pinz's lose stability in places they shouldn't have, and the inherant instability of swing axles is why Ralph Nader became a household name in international Automotive circles in the 1960's and 70's.His book ''Unsafe At Any Speed'' ultimately killed off the use of swing axles by car manufacturers in the western world.

bill.

[FridgeFreezer]

Whilst talking of the Frog, I've observed that it and many other Lagoda type vehicles are extremely short and high, which seems to suggest to me that there aren't too many steep offcambered hills in the event. True or false?

I'd say false, it's not exactly a rock-crawlin' competition but stability is required and there is plenty of slopey stuff. The frogs can jack themselves up & down, they can tiptoe over things and then hunker down for a bit of speed work.

Some of the cars are quite tall, but then some of the oily bits offset that to a degree. On 40's and portals there's only so low you can make a car and still have room for legs.

[plasticbadger]

Comment back to original chat of independent vs. live axle:

All the american rock crawlers and australian tuff truck guys swear by live axles. Yes they are heavy and you can't articulate without effecting the other wheel (and all the other things people have poined out), but the critical point is as follows:

By the time you've made the arms / links / cvs / shafts strong enough to ake your LS3 / 40" tyre / portal box combination you've not only invested a hugh amount of money and time in custom development, but the un-sprung weight is getting pretty high anyway.

I can understand the independent route on a smaller machine (Frogs and Simonr for example), but when you're into the 400bhp+, 40" tyre realm surely live axles are worth considering.

This is one reason why the Hummer doesn't gain ground clearance with it's drop boxes. The arms etc have to be so big and orientated so low to handle the torque realiably.

[callum]

to go away a bit, but still on the subject of suspension, what are the drawbacks of splitting the links either side of the axle i.e bottom back and top front.

i finally found some auverland suspension pics, looks like an interesting setup up front

assuming your engine was mounted far back enough and your setttering box was moved outboard, could a land rover run this setup up front?

pics should be reasonably self explanatory

however if anyone wants to add further explanation of how it works, feel free

pics from this thread on difflock

http://forum.difflock.com/viewtopic.php?p=...2cf865b61a5629d