The advantages of independent suspension or not?

[Chicken Drumstick]

Hope this is the right place to post this. But I thought it seemed the forum with the most technical talk, and this sort of thing fascinates me.

Considering the 9 out of the past 11 new Land Rover vehicles run independent suspension. I wondered if it was worth discussing the merits such systems have off road?

It's something that has been bugging me for ages. I know the good'ol live axle works off road well because as one wheel is pushed up, it pushes the other down. And I know on certain models Land Rover they can do some clever stuff with cross linked air suspension to simulate this.

But how good off road (typical Defender use, rather than off road racing) can IFS or IRS actually be vs a live axle?

Can you really get the same sort of travel from an independent system?

Also looking at the wider market, almost all 4x4's and utility off roaders run IFS these days, but often with a live rear. Now we all know the LR front suspension on a Defender has limited travel, would an IFS Defender really hurt it's true off road ability?

For example, looking at an IFS truck like this:

Is the articulation mostly coming from the rear live axle? It looks it to me. So how bad would it be or how unstable would it be if the same vehicle was equipped with IRS also?

[Tanuki]

Independent suspension has the big disadvantage that a wheel can get pushed right up inside the arch but the differential etc. is still hanging down and can ground-out on the typical "hump" down the centre of a rutted track.

With a beam-axle, push the wheel up and the diff rises too.

OK, for high-speed towing and heavy-laden work on ordinary highways I'll go for fully-independent and air-suspension every time because of the extra stability it gives you. In all honesty and 30+ years of Defender driving I've never found my progress impeded by lack of suspension-travel - the problem has usually been grounding-out the rear towbar on the previously mentioned hump in the middle of a track. This problem is addressed by either taking a run at the obstruction, or driving the obstruction in reverse!

[zim]

Shannon Campbell's buggy from the US

[Chicken Drumstick]

The IFS/IRS racing buggies are hugely impressive. But is such a setup impractical for most road vehicles due to the length of the upper and lower arms?

[simonr]

Most of the implied criticism of IS comes from people who have not tried it in anger!

I have!

I built a truck with Jaguar differentials (same insides as Sallisbury) and 14" travel. The suspension hit the bump stops at the point where the diff would be the same distance off the ground as a beam axle and the wishbones were as long as I could feasibly make them. Similar geometry to the above.

It lost nothing in articulation nor bellying out - but gained a great deal in stability. The wheels tended to stay on the ground more of the time, which was a big deal on bumpy hill climbs. It could climb where no beam axle would go. In a similar vein, you could hit the bottom of some slopes faster because it would soak up the undulations before the slope which would make a beam axle bounce on to it's roof.

My conclusion was that if you design Independent Suspension to have the same performance envelope as a beam axle, it will - but it gives you a few added benefits at the expense of a little extra complexity. The trouble is, and where most peoples skepticism comes from, is that there are no (few) commercial IS vehicles built with off roading in mind in the same way as a Defender - and compared to one, they (obviously) don't deliver.

I for one would be keen to see a Defender with IS - and would not rule out any vehicle because of it!

Si

[Chicken Drumstick]

Thanks for the insight Si. Do you have any pics of your off road IS setup? (I think I may have seen some early snaps while you were still building it).

BTW - what are your views on the off road ability of the D3's independent suspension? I know the vehicle as a package stacks up well. But on a more technical level, did LR get it right? Would the D3's suspension on a Defender work, should LR decide on this route with the Defender replacement?

[Soren Frimodt]

Interesting subject to bring up.

I myself do not particularly like IFS on a 4x4, but then again all my experience comes from cars with a factory setup that, as Si states, isn't ideal for offroad performance. But furthermore I've raced a fair amount of Quads through the years, and been on many of the same climbs etc as I've been on with my 4x4's. And on the Quads I didn't find it favorable either.

First off I think it is too comprehensive and if made to really last, quite heavy and/or very expensive to build. Then there's the disadvantage as to bring even more CV's into the equation, the one component that already gives us grey hairs on our 4x4's

And basically I do not like the way it behaves, the car becomes much more 'dangley' and unstable when crawling on obstacles that requires a lot of suspension flex. Much like driving a leafsprung 4x4 actually. Although I would say that the leafsprings are more predictable as they do not have as much 'rebound', an IFS system can kinda push the vehicle over at certain situations because the spring applies so much force on the one wheel that's at the highest point, inducing more body roll than necessary. But again remember, this is just my experience.

If you go mudding a lot however, they are a lot better, much smoother underside of the vehicle and no diffs or axlehousings to drag through the mud.

Independant suspensions does have their place in my book though, as I drive a '71 Jaguar as my daily driver I can assure you NOTHING even comes close the ride of this thing, it is super nice to drive, stiff yet soft and takes bumps like was it driving along on 35" tall tyres

[simonr]

Chicken (do you have a real name?) Drumstick, I don't think Land Rover did a bad job actually! The setup has 12" travel before anything binds, though that's not fully utilised in the standard setup, and it's very strong. The drive shafts make Defender half-shafts look like matchsticks!

I've seen a RRS off roading (in Sand). It belongs to my friend Graham (Rocker on here) and although it lacked the clearance of my Defender, and was on road tyres (and he was afraid to boot it because of potential damage) - I was nothing but impressed with where it went! To the extent that I'm going to buy one to see what I can do with it!

In 10 years time, most of the off roaders will likely be based on this platform - and we will view the 'oldies' running beam axles, in the same way as we view 'leafers' now! I think the D3/4/RRS suspension setup with a bit of modification could out perform most of the not too extreme beam axle trucks. It's never going to win RTI challenges - but how often in real off road situations is that critical? More often it's stability on side slopes and being able to find traction while moving on bumpy ground (hill climbs in particular) - and (if set up correctly) in these situations, it's a winner!

I was a skeptic until I was photographing a challenge (some time ago) and there was a Suzuki Vitara competing. I spent most of the day at the foot of one climb and the only vehicle I saw climb it without winching was the Vitara! It was obvious that it was the IFS more than the weight that allowed it to do it as you could see it's wheels stayed in contact with the ground. A diff lock or beam axle doesn't help you when you are airborne! It was that day that persuaded me to build one!

Soren - all the things you have experienced could be matched by a beam axle vehicle depending on how the suspension is set up. The same is true for IS, it's just that the IS cars you can buy are set up for driving on the road, whereas an absolutely standard defender is configured with more off road bias and will out perform the former off road.

Si

[FridgeFreezer]

Be interesting to see how this goes, I predict it will be very hard to arrive at solid facts as there are not many examples where you could pick two very similar vehicles (same platform), one with indy, one with beams, and compare them side-by-side. There will also presumably be a driving-style problem, if you drive an indy as if it had beams you're more likely to come a cropper, but that's not necessarily the fault of the setup.

I know there's a few pickups etc. where they can be IFS or beam, the beam ones being "heavy duty" or whatever.

As with many of these technological advances, there's plenty of people who will swear blind the old version is better and the new one can't possibly be any good / is too complicated etc. well beyond 50% market saturation.

My limited experience is that Freelanders are rudely capable as long as you don't follow Defender-size ruts, but of course it's helped by ETC and lightness, hindered by road tyres and no low-range...

There was an independently suspended Series prototype back in the day (something to do with competing with the Austin Gipsy?), from memory it was evaluated by LR and the Army and found to be no better, but more complicated. How that would stack up these days with modern bits is another guess.

[Daan]

Shannon Campbell's buggy from the US

Be interesting to see how this goes, I predict it will be very hard to arrive at solid facts as there are not many examples where you could pick two very similar vehicles (same platform), one with indy, one with beams, and compare them side-by-side. There will also presumably be a driving-style problem, if you drive an indy as if it had beams you're more likely to come a cropper, but that's not necessarily the fault of the setup.

I think it is very straightforward to pick two similar vehicles; At the king of the hammers, there are very comparable vehicles with beams and indy suspension. They perform differently from each other in that the fast desert sections are usually favouring indys, while the rock crawl sections are favouring the beam axles. Which wins pretty much depends on what mix of rock crawl and fast sections the organizers decide to go for. In my mind, that explains the story.

Daan

[tacr2man]

If you want a comparison at the top of the tree for off road , look at a Tatra V MAN

Driving a stalwart will also sell you on IS . The big trouble with IS on smaller vehicles is trying to make it strong enough without becoming very heavy , and the complexity , wheareas a beam axle is very robust without the cost.

Ride is improved , but as landrover discovered with rangerover going to coils , they had to beef it up to stop breaking it as the off road speedlimiter (damage to driver) as with leaf springs didnt come into operation untill higher speed

[De Ranged]

IFS is the future but not untill a major manufacture builds something reliably worthwhile and this isn't going to happen in the near future as there isn't a demand that warrants the increased cost of design and building, currently over here the only setup that is worth using off road is the Mitzi Pajero front end

From an offroad performance stand point the bonus's for IFS are, tunable camber (keep the tyre surface flat for better grip this in reality is marginal as we run lower tyre pressure to gain bigger contact patches and the lower pressure will allow this anyway), lower unsprung weight (allows the wheel to stay in contact with the ground when going faster), diff height can be raised (depends on the CV angles), better packaging (the fixed diff head allows you to package the motor better for a potential gain in CoG)

The flip side, expense (more moving parts the higher the expense), complexity, strength (due to the fact the first buyer of a 4wd now buying it as family mover there is no gain to the manufactures to "overbuild" they build to the intended use and it just isn't up to abusive 4wd'n) now for the fun stuff... a low roll centre height( I know some of you will say that IFS is more stable on a sideling and a lifted "cranked" up suspension is but this is due to increased preload on the spring costing articulation, IFS because it works across the vehicle has to have a low Roll center to make it ride comfortably or as you get body roll the "feel" of the vehicle changes because the roll centre height changes, on a beam axle truck you can make the roll centre high and the suspension will resist body roll for a more stable feel because the only time the roll centre changes is under brakes or acceleration

If you want a better question why not ask what traction control is going to do to 4wding

[simonr]

De Ranged - good answer!

Si

[discomikey]

i feel that another limiting factor to the ability of the standard IFS trucks, is that the majority of them are sprung by torsion bars, which IMO are really quite slow to respond to quick osscilations, eliminiating any gains to be had from the reduced unsprung weight.

that is what makes the older navaras, L200's, and hiluxes seem so boaty and wobbly at the front. whereas look at newer models, the "rounded" L200 for example, with coil front IFS, it can react much better and i have experienced the difference.

Although the systems in these standard forms don't look as impressive, this is generally due to the lack of travel which could be improved on, with the aid of traction control systems like on the D3/4/RRS etc, they are unstoppable on road tyres and i personally cant wait to see the day someone puts a set of simex on a D4 to see what it could actually do.

[discomikey]

a roll center point too, in theorey it is possible to create a vehicle that will naturally lean into corners and more importantly side slopes, just so long as you can get the COG below the roll center. thats the hard bit!

[bill van snorkle]

The American King of the Hammers competitors such as Shannon Campbell have thrown thousands of cubic dollars at developing indy suspension, yet they can only just come close to the performance of beam axles in the rocks, by virtue of having very wide wheel tracks. Notice Shannons rig still runs a beam axle at the back.

IMO Tatras are not a particularly good example to include when discussing the virtues of indy suspension. Tatra swing axle suspension is broadly similar to that of Pinzgauers, the 4x4 version in particular being one of the most unstable, and without their difflocks engaged, least capable offroad vehicles I know of when the going gets gnarly.

An experienced and capable driver who owns a coil sprung Disco 3, avoids some of the really twisty sections of my trials coarses, stating that whilst the traction control is very good at keeping the truck moving, the limited suspension travel will see it lying on its side well before the point where his previous RRC would have a lie down.

[n.r.g97]

There are merits and hinderances to every system, however reliability has to be important.. John Sales 'Bulldog' seems to have trouble with that with the independant suspension, however i do still think that once someone puts time and thought into it, it could rival beam axles, at least at the higher end competitions, at a low end i dont think people are prepared to spend that much money and time on a system that is fairly unproven, especially on something that needs to be used on and off the road, im not sure a comprimise would work well. Saying that the comprimise between offroad and offroad capabiltys is often not perfect with beam axles...

http://forum.difflock.com/viewtopic.php?t=14499&start=600

I think this idea has alot of good points and it would be well worth investing some time into it.

[bill van snorkle]

http://forum.difflock.com/viewtopic.php?t=14499&start=600

I think this idea has alot of good points and it would be well worth investing some time into it.

Nice fabrication work, but I don't understand the suspension medium. Are those Air Shocks? And are they cross linked ? If the shocks had any spring rate at all, I can't see how they compress so readily during articulation under such a light vehicle. All the bits of tube that constitutes the lower control arms below the axle centreline brings up another point about Indy susp. Unless a flipped Jaguar design is employed, where the halfshaft doubles as the lateral lower control arm,then ground clearance below the halfshaft is usually compromised.

[simonr]

That's almost just a prettier version of what I built! Using hydraulics to rotate the sub frame which the Indi attaches to. If you cross-link the two rams which force articulation - it works reasonably well. Mine originally just floated - which worked very badly. Added the hydraulics which made it a lot more stable.

The big issue was that if you are climbing a side slope diagonally, it's only the down pressure on the down hill rear wheel which is holding the up hill front wheel on the ground. With diagonal cross linking, there is none which causes the front to lift off and effectively roll over, dragging the back with it. I rolled it 360 degrees on a fairly trivial side slope which I've since driven with ease in my 110.

Mine had the lower wishbone in the same plane as the drive shaft - so the clearance was actually better close to the wheel than a beam axle.

It was a worthwhile, educational experiment - but for the next build I went back to beams just for simplicity!

Si

[missingsid]

I am not very technical but love chalenges, as far as I can see you need long travel which in turn needs long arms.

This then results in very narrow chassis spacing (truck shown by Si) or a very wide truck with still limeted chassis spacing as in Humvee.

Niether of these designs would suit a Defender type application I would have thought?

Marc.

[simonr]

For a 'future' project, I was thinking about making the chassis run around the outside of the vehicle - almost like rock-sliders and hang the wishbones from the opposite side of the vehicle above the opposite wheel arch. Then mount the differentials on a 'pendulum' which, via a control rod sits at an angle proportional to the mean droop of the two wishbones (to minimise the sliding joint lengths). This would potentially give you a roll centre above the CoG (so it leans in to bends) and because the wishbones will always be angled down (due to the high mounting point), you can never get in to a situation where the clearance is less than it would be with a beam axle.

It would obviously need to be mid engined (not a bad thing) and a real space frame (also not a bad thing) with the passenger cell suspended inside the frame. The steering linkage, if fully mechanical, is more tricky. The simplest I've come up with is similar to the steering linkage on a Vitara with a bar running from one chassis side to the other connected to swinging arms (bolted to the chassis rails). Long control links following the line of the wishbones and a more central steering box which moves one of the swinging arms.

Hydrostatic drive would make the whole thing easier (I've been looking out for a scrap crop sprayer!).

Si

[Snagger]

I think that it's a real case of apples and oranges. They're very different systems with very different characteristics, and as such are used in different applications.

IS is certainly more comfortable and compliant at speed, with much better stability. Live beam is better where ground clearance is an issue. The thing is, you won't be doing high speed, needing the stability of IS, if ground clearance is an issue, and so LB will do the job in those circumstances amply. Likewise, most vehicles that drive at high speed won't need the ground clearance of LB, so again, they don't need a compromise system, like the buggy in the photos or Dakar racers - they don't rock crawl or cross ditches and bomb holes.

LR have been ingenious in their use of cross-linked IS on the new models, which gives the best of both words - the only compromises are complexity and cost (the former being a major consideration for use in remote locations).

If you can come up with a system that gives the advantages of IS and LB without the complexity of cross linking, I think you'll soon be a rich man!

[elbekko]

For a 'future' project, I was thinking about making the chassis run around the outside of the vehicle - almost like rock-sliders and hang the wishbones from the opposite side of the vehicle above the opposite wheel arch. Then mount the differentials on a 'pendulum' which, via a control rod sits at an angle proportional to the mean droop of the two wishbones (to minimise the sliding joint lengths). This would potentially give you a roll centre above the CoG (so it leans in to bends) and because the wishbones will always be angled down (due to the high mounting point), you can never get in to a situation where the clearance is less than it would be with a beam axle.

It would obviously need to be mid engined (not a bad thing) and a real space frame (also not a bad thing) with the passenger cell suspended inside the frame. The steering linkage, if fully mechanical, is more tricky. The simplest I've come up with is similar to the steering linkage on a Vitara with a bar running from one chassis side to the other connected to swinging arms (bolted to the chassis rails). Long control links following the line of the wishbones and a more central steering box which moves one of the swinging arms.

Hydrostatic drive would make the whole thing easier (I've been looking out for a scrap crop sprayer!).

Si

Sounds a bit like a TTB but without the massive camber changes?

[simonr]

TTB?

Si

[elbekko]

A suspension set-up used on Ford trucks (IIRC). It's somewhere between a solid axle and IFS.

http://www.pirate4x4.com/forum/newbie-general-4x4-discussion/873239-school-me-ttb-axle-set-ups.html

http://en.wikipedia.org/wiki/Twin-Traction_Beam