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Suspension Systems


Corrode Finger
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Have been having a conversation tonight about suspension on an offroader, that has got me a wondering?

Conventional landy suspension has a beam axle with coils and dampers or leafs and dampers.

When traversing rough terrain, the beam rotates centrally and the opposing wheel reacts to the other wheel.

Do you have to have a beam axle to make the suspension work offroad?

Can wishbone independant suspension work?

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A beam axle is considered superior when traversing rough terrain, as the weight is distributed more evenly between both wheels. With independant suspension, the highest wheel takes a lot more weight and the lowest one has more tendancy to spin.

To counteract this, new Range Rovers have left-to-right coupled airsuspension, which in fact mimics a beam axle to some extent.

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I feel it is conceivable to have a suspension system with upper and lower wishbones attached to a croosmember centrally pivoted to the chassis. The pivot could be locked for roadwork or could be made with variable roll resistance. This arrangement would give the advantages of low unsprung weight of independant suspension and the cross axle ''see saw'' effect of a beam axle.

Bill.

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So, beams are better, but is that because they are more familiar?

As mentioned, with the Rangey comments, the independant systems can work but require active systems to make the setup work.

Also the question has come about partly through consideration of 'buggy' type vehicles, therefore reducing weight, which i assume will have an affect on the characteristics of the suspension, again as identified, one wheel takes the load while the opposite does not.

Can this problem of a free spinning wheel be overcome with lockers?

Can trailing arm type systems work, like the rear of bikes?

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So, beams are better, but is that because they are more familiar?

This is my assertion.

Lots of people say Indi is no good off road - but based on what evidence? I've only found two people who have actually tried it!

For most other people it is at best second hand and at worst just an assumption because everyone else says so.

The commercial off-roaders with indi suspension, only have it on the front, and have almost no travel. For example 4.5" on a Suzuki Vitara.

A beam axle is considered superior when traversing rough terrain, as the weight is distributed more evenly between both wheels. With independant suspension, the highest wheel takes a lot more weight and the lowest one has more tendancy to spin.

To counteract this, new Range Rovers have left-to-right coupled airsuspension, which in fact mimics a beam axle to some extent.

There is an element of truth in this, but only in so far as when you push a wheel up, the axle pivots around the compressed spring and pushes the other side down (but because of the position of the fulcrum, with only about 15% of the force). This is the argument used to support spring dislocation, that the other wheel is causing the dislocated wheel to be pushed down - but the down force is small.

I believe the actual reason for the RR coupling is that with IFS, when you can push one wheel up, the other wheel stays where it is. This means that the diff will get closer to the ground (by half as much as you have pushed the wheel up) - leaving the diff / chassis scraping on the ground.

By cross connecting the bags, it reduces the dipping of the diff thereby increasing mean clearance.

However, this also leads to a problem - instability. Imagine you have crested a hill (fast) and the first wheel to touch the ground lands in a hole. the spring on that side compresses, but there is a force pushing the other wheel down, which gives the body a kick towards the hole. However, there is a delay in this kick due to the inertia of the axle. All these forces and delays make it hard for the driver to predict how it is going to behave, particularly as you reach the limits of the vehicles stability.

Most of the time when people speak of 'handling' in cars etc, it just means making the car easy to predict how it will behave in a given situation. That is the biggest plus of indi suspension - that the handing is easy.

Indi gives you the lowest possible un-sprung weight. The reason this is good is that the wheel has less inertia and momentum. This means it requires less damping, which means the wheel can move up & down faster allowing it to stay in contact with uneven ground more of the time - i.e. more traction!

Seeing the way I can drive my quad around, the way the suspension soaks up bumps that would throw a Land Rover on to it's roof just makes me think that indi suspension has a lot to offer. Different things to beam axles albeit but hopefully enough to be competitive.

Building something is no mean feat though - particularly if you want to make your own uprights, wishbones, links - everything. I keep wondering why I didn't just buy a couple of axles to stick on this buggy and it would be moving by now!

Si

Front_Setup.pdf

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Simonr,

You have articulated(bad pun) what i have been considering, ultimately, i realise that making something from scratch has issues.

Would the same issues with wishbones apply to all types of independant suspension, as asked above, trailing arms, obviously a rear setup, or macpherson struts for the front, with a suspended hub and lower wishbone?

Also does any active system such as the new rangey setup cause issues?

From what i can determine, the active setup is really to enable clearance to be maintained rather than ensuring that the system actually works.

The pdf is impressive, is that something you are doing/ or contemplating?

The 'seed' for the question was the setup of the vitara, apart from limited travel, is there any fundamental reason why it does 'not work'?

Many questions, i know, but i am on another fact finding and question search to improve my knowledge, similar to the portal thread i started.

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Would the same issues with wishbones apply to all types of independant suspension, as asked above, trailing arms, obviously a rear setup, or macpherson struts for the front, with a suspended hub and lower wishbone?

IMHO double wishbone has the least problems. You can get some of the advantage of trailing arms by inclining the 'hinge' for the wishbone up at the front. Thus when you hit a step, pushing the wheel backwards, it moves up as it goes back, hopefully clearing the step.

macpherson strut is simple, but for long travel, you put a lot of stress on the damper. They are only used commercially because they are cheap with fewer parts and very compact. For a number of reasons they do not deliver the handling you can achieve with double wishbone.

Also does any active system such as the new rangey setup cause issues?

From what i can determine, the active setup is really to enable clearance to be maintained rather than ensuring that the system actually works.

Air bags are too easily punctured. the only ones available with enough travel have too big a volume which means low air pressure which in turn means low spring rate, which means that it hits the bump stops all the time unless jacked up really high.

The pdf is impressive, is that something you are doing/ or contemplating?

I wouldn't like to say! ;)

The 'seed' for the question was the setup of the vitara, apart from limited travel, is there any fundamental reason why it does 'not work'?

You should make contact with Tony (Suzota) on Difflock.com He's building something cool out of a vitara with double wishbone but largely out of vitara parts. It looks good so far and he has got a lot further than me!

Si

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With regards to the limitations of the airbag sytem, could a Hydropneumatic/ Oleopneumatic system fullfil the criteria, the system that i have to mind is the Citreon(spelling?) system famously used on BX's and CX's, XM's etc?

This is an active systems which does not have the low 'pressure' issues associated with it due to fluids?

I do not know, i am an inquisitive novice in this arena.

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A good friend of mine is building a comp safari racer from scratch and has an independant suspension setup very similar to the one on Simons pdf. I will ask him in the pub tonite if its OK for me to give you his phone number Simon, I think you would be very interested in what hes built so far.

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This is something we were looking at back home for my friends Blitz. but the main issue we have is lack of travel on Indi. some ideas banded about was Scooby based stuff. Tony's tryggy is certainl an intersting looking thing and i am also keen to see how he is coming along wiht it!

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Air bags are too easily punctured. the only ones available with enough travel have too big a volume which means low air pressure which in turn means low spring rate, which means that it hits the bump stops all the time unless jacked up really high.

Spring rate can be addressed by varying the diameter of the lower spring locator / mount which the rubber bag rolls down and over as the bag compresses. The wider this is, the higher the spring rate that is acheived. This is an issue which the latest Gen3 Airbags from Arnott adress on the P38 RR springs. OEM airbags had a thin section when the RR sits in motorway height. The Gen3's have a wide section to make the motorway height have a much stiffer spring rate when lowered to improve handling. Custom lower mounts to acheive varying spring rates at varying stages of bag compression would be simple to make by running off a lower mount on a lathe and then cobining that with a locator plate to suit the mount on the axle.

In terms of the vunerability of air bags . . . yes, i guess that can be an issue, but it would vary on the situation that you are using the air bag. Lots of large stones / branches / logs can come up and puncture an air bag. But at the same time, they owuldn't need much in the way of protection to prevent all but the worst of hits. In a double wishbone setup, if the air bag where contained within the wishbones, then it wouldn't really be all that hard to mount a form of protection guard on one of the arms to stop things hitting it ( grill plate etc ).

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With regards to the limitations of the airbag sytem, could a Hydropneumatic/ Oleopneumatic system fullfil the criteria, the system that i have to mind is the Citreon(spelling?) system famously used on BX's and CX's, XM's etc?

This is an active systems which does not have the low 'pressure' issues associated with it due to fluids?

I do not know, i am an inquisitive novice in this arena.

How about Hydralic suspension - its big in Aus at the moment. The idea is you have a coilover but that you can vary the position of the top mount and so lower and rasie the ride height / push wheels onto the ground. Very bling but quite complicated. It might be fun to play with but I thinks there's a lot to say for simple coil overs as they're pretty tough and if you end up with rear steer, twin lockers, fiddle brakes and hydralic suspension there's a lot of levers to pull!

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Independent for me seems too fragile at least in "factory" spec... Baja racers are a bit different in engineering terms and £££ too!

My thought is that if you biff a beam axle on a rock it doesn't bother it much, if you biff independent suspension on a rock (or have a heavy landing or hit a buffalo ditch or any number of other things) you are likely to twist the suspension mounts which means unless you have the kit to realign it all from scratch (not available in this part of the world) the vehicle is scrap. I know of a Freelander that had exactly this happen to it and wears out tyres in about 6000 miles.

I also don't know how long suspension bushes will last on independent, I know some Mitsubishis round here that make some bluddy awful noises from their front suspension! LR beam axle bushes are dead easy to change and not that expensive, I doubt the same is true of independent.

IMHO beam axles might be old tech but they are tough and that's probably most important. A bit like comparing a Tdi to a modern tech common rail diesel which sneezes and illuminates a forest of warning lights at the first sign of even slightly non EU spec diesel.

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I did a bit of research in to suitable bearings for the wishbones - and have found a company called Igus who make polymer bearings. In particular, they do one designed to run in abrasive environments - so that's what I have bought. Time will tell if it was a good move.

Strength may be an issue - again, only trying it will tell!

Will - have you been spying on me? Electric rams - that's the way forward!

Si

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I built the Rock Rod completely from scratch with independent double wishbones all round. Using Mitsubishi uprights at each corner and OEM upper and lower ball joints it wasn't that difficult. Not that it was designed for road use so its probably fair to say that tolerances weren't that great.

It worked fine off road with plenty of travel and good articulation, the only problem was lack of weight at each corner which really needed lockers to ensure better traction.

I did play with developing ETC on it but the weight of the wheels and tyres was too much for the puny LR ABS pump.

There is a lot of scope for indi suspension but few people have the patience to persevere.

The scandinavians have a neat system for moving the upper mounting of a coilover with a simple cam arm and short hydraulic ram.

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For speed

I have raced on Beam axle and indi

I prefure indi and was told be some very respected racers that racing the tomcat would be a step backward for my driving stile.

All the fasted racers are indi. Milner pro truck, ammaratti , Mattsarati , Mitubushi Evo 3

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isn't this a question of fitment for purpose?

Indi is surely very good at high frequency short to medium amplitude shocks- perfect for offf road racing where you rarely "want" one wheel to be fully compressed.

Beam axles are clearly good at low frequency but medium to high amplitude movements- perfect for winch challenges and the like.

If we did more "special" stages against the clock then indi would undoubtedly have more of a following- Rog (istruggletogate11) had a really nice rock buggy which had indi suspension- unfortunately never got to see it running for real but the piccies and vids suggest it was very effective.

There is a camber compensation system which you find in kit cars (and some race cars) which links the two wheels together and negates camber changes during high speed cornering. My brain is nowhere near clever enough to work out whether or not this system could be altered, but i suspect if it could you would end up with a system wtih all the benefits of indi and beam axles. All i need to do now is go and get an engineering degree- back soon...... :D

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Just to upset the applecart; the vehicle that won Ladoga last year was indi....

So, making a statement like that Mr Warne, requires someone, to provide some info?

Equally, going back to the hydraulics, thats the logic behind the Citroen esque system, but thats gas and fluid, thereby making spring and damper as one. Anyone a closet Citroen geek?

Can appreciate that indi is better for speed in a comp safari point of view, but i was coming at this from the slow, mud plug and climbing over stuff view point.

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I know nuffink - Jez might know a bit but it is all fairly mysterious, they're not about to give away any info about it, those are spy shots taken by one of the Finnish perverts at Vippsky Les and TBH even looking at them closely I can't work out how most of it works.

I'm guessing there may be chain drives to the rear wheels, god knows what to the front, no idea what may pass for a transfer box. You can see some sort of airbag on the suspension but but there must be more to it... All the buttons in the cab to control it are marked with things like "rocket boosters" "ejector seat" "missiles" etc. to keep people guessing :lol:

I think anyone who HAS worked it out is going to keep bloody quiet while they (try to) build their own. There have been various theories about how it works but nowt that makes you go "Aaaah, of course!" just possibilities that seem semi-likely but difficult to make work. I know it spent a lot of time on a trailer between stages at Ladoga, either through genuine mechanical failure or because it's somehow allergic to tarmac.

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