Suspension Systems

[bill van snorkle]

Peter Phillpotts of Off Road design did this some years ago. I have an independent racer with Landy hubs, stubs and 110 outer CVs. The uprights are fabricated. It uses BMW diffs, the last LSD super strong diff was £40

It manages 13.5 inches of wheel travel. I have about 12" clear under the car everywhere on 235/85/16 tyres.

Couple of otherpoints, you get a smooth underline with an indy and the wheels are nearly always in contact. Last safari I was able to take a rough short cut that the axled boys couldn't get over

That is very interesting Steve. Would you happen to have any pics of your front end layout ? If you are using 110 outer assemblies would I be correct in thinking that your front end has three constant velocity joints on each side, instead of the traditional two per side of conventional independantly suspended front wheel drive systems?

Bill.

[ashtrans]

I vaguely recall reading oh so many years ago (maybe 20 or so) in a very early(black and white I think) British offroad magazine, a fairly detailed article about a company that converted RangeRover axle assemblies to independant for safari type racing. They chopped the banjo housings short, made short flanged halfshafts, Open CV jointed driveshafts to the standard RR swivel and hub assemblies. there was a bracket bolted to the swivel ball flanges and rear stub axle flanges to which the indy control arms attached. I can't remember any other details but do any of the forum members have any knowledge of this conversion and how successful it was in a variety of conditions?

Bill.

My father, Ian Ashcroft made some of these many years ago for a couple of the comp safari racers of the day, from what I remember they were :

a rover diff and stock beam axle,

chop each side of the axle casing a couple of inches from the diff side gears,

bore a hole in a rectangular 6mm steel plate,

fit a round collar in the plate hole,

press a top hat bronze bush in the collar and oil seal

weld plate to each side of axle housing

make 2 splined (bored 12mm) stubs, like a mini halfshaft 6" long

make 2 drive flanges

use a long bit of studding from flange to flange to hold it together,

you can use the ends of the rectangular side plates and the steering damper mounts holes (in the diff housing) to mount the diff,

[simonr]

That sounds cool Dave. I considered similar - but was put off by having to make my own shafts!

Doing this instead. Not the clearest photos I'm afraid. Not made wishbones yet - it's all held together with monster cable ties!

Si

[bill van snorkle]

My father, Ian Ashcroft made some of these many years ago for a couple of the comp safari racers of the day, from what I remember they were :

a rover diff and stock beam axle,

chop each side of the axle casing a couple of inches from the diff side gears,

bore a hole in a rectangular 6mm steel plate,

fit a round collar in the plate hole,

press a top hat bronze bush in the collar and oil seal

weld plate to each side of axle housing

make 2 splined (bored 12mm) stubs, like a mini halfshaft 6" long

make 2 drive flanges

use a long bit of studding from flange to flange to hold it together,

you can use the ends of the rectangular side plates and the steering damper mounts holes (in the diff housing) to mount the diff,

I prefer the yellow cable ties Simon. I believe the tensile strength is 5% greater than the other colors.

Dave, Did your father do it for the engineering challenge ? or was there a a rule in comp safari's that stated mostly Rover components be used? I would have thought, particularly in the UK at that time that the Jaguar Sals/Dana44 indy diff with the very good Sals Power Lock LSD would have been a stronger, easier and better choice than modding the Rover diff.

Whilst on the subject of Jags, They use their axle driveshafts, with very large UJ's as the upper lateral control arm of the suspension, with an additional lateral link below it. It seems to be a simple elegant solution that works for that type of vehicle, but would compromise ground clearance on an offroader. Simon, have you considered the Jag design, but mounting the lateral control arm above the axle driveshaft?

I regret that due to circumstances pretty much beyond my control that my days of hands on vehicle modification are now over, Aside from maintaining what I already have, I am reduced to being a Web engineer and maybe even a web wheeler that can merely offer suggestions that may or may not work.

bill

[will_warne]

What Ian did is very close to what I'm planning to do: Take an axle case and cut it down. Take a pair of stub axles and remove the stubs. Weld these onto the cut down casing so the CV stubshaft takes drive from the diff. Onto the new axle end will fit a modified swivel housing and swivel ball which then mounts to a longitudinal control arm. Think Pinzgauer but with MUCH longer arms

Si, there's a huge amount of work that's gone in there! Looks good, though!

[bill van snorkle]

What Ian did is very close to what I'm planning to do: Take an axle case and cut it down. Take a pair of stub axles and remove the stubs. Weld these onto the cut down casing so the CV stubshaft takes drive from the diff. Onto the new axle end will fit a modified swivel housing and swivel ball which then mounts to a longitudinal control arm. Think Pinzgauer but with MUCH longer arms

Si, there's a huge amount of work that's gone in there! Looks good, though!

Will, What advantages do you think the old swing axle type of suspension system you have described will have over regular independant suspension? You no doubt have seen some of the various videos on the 8x8 Tatras in action, and may have observed the scary amounts of camber change and effective wheel track narrowing as the suspension cycles through its very limited range of travel. Whilst the vehicles look spectacular in those Euro truck trial events,I believe it only looks that way because Tatras make a real meal of obstacles that a beam axled 8x8 such as a MAN would barely notice.

In your proposed design ,If you only have a single longditudal control arm then it will have to be a radius arm of some type, which will also cause each wheel to be pulled for and aft slightly through its range of vertical travel which may give unwanted and undesirable roll/bump steer. Unless I am overlooking something here all I see is a whole bunch of negative characteristics and no positive ones.

Please enligten me.

Bill.

[FridgeFreezer]

Will, I can't help but think that imitating a Pinz setup is a backwards step, they don't seem to be the most capable or stable vehicles I've ever seen. In fact everything I've heard about them suggests they're surprisingly poor

I would also say Bill has a point about making indy setups from LR bits - why would you bother when you can buy BMW / Jag diffs and get a much better unit? My cousin bought a Z3 LSD for his 3-series for £40 the other day, and they just don't break.

[simonr]

Bill, the Jag design is similar to what I'm building!

The trouble with using the drive shaft as one link is it only restrains the upright in one axis. If the wheel is just moving up & down, that's not too much of a problem. If you introduce steering, the joint on your single wishbone becomes complex and big!

The way I'm approaching it is to use upper and lower wishbones. The drive shaft still provides rigidity stopping the camber changing. The bottom wishbone has an elastomeric bush allowing it's length to change slightly (only a couple of mm) which means the suspension will not bind up so easily (since I have in effect three wishbones). It will mainly be responsible for caster control on which axis the bush is rigid. Since the tensile force of the bottom wishbone will be reduced by this arrangement, I'm going to bend it such that the middle of the wishbone is higher than the ends. This improves clearance as the wishbones droop but will not affect the strength to too great an extent (particularly with a fin welded to the top of the arch as a gusset)

If the elastomeric bush thing does not work - I'll look into getting drive shafts with plunge joints instead.

I'm also going adjustable height using electric linear actuators to move the spring hanger up & down. This means that the wishbones are best off parallel. Non parallel or different lengths can be used to give you camber gain on compression which improves handling a bit. However if the height is adjustable, the camber would only be correct at one height.

Will. Interesting. I would have a look at a book called Chassis Engineering by Herb Adams. He's very non judgmental about different configurations, just gives the pros and cons of each. You can then make a pretty informed choice as to what path is likely to take you where you want to go.

Si

[will_warne]

Bill, the Jag design is similar to what I'm building!

The trouble with using the drive shaft as one link is it only restrains the upright in one axis. If the wheel is just moving up & down, that's not too much of a problem. If you introduce steering, the joint on your single wishbone becomes complex and big!

The way I'm approaching it is to use upper and lower wishbones. The drive shaft still provides rigidity stopping the camber changing. The bottom wishbone has an elastomeric bush allowing it's length to change slightly (only a couple of mm) which means the suspension will not bind up so easily (since I have in effect three wishbones). It will mainly be responsible for caster control on which axis the bush is rigid. Since the tensile force of the bottom wishbone will be reduced by this arrangement, I'm going to bend it such that the middle of the wishbone is higher than the ends. This improves clearance as the wishbones droop but will not affect the strength to too great an extent (particularly with a fin welded to the top of the arch as a gusset)

If the elastomeric bush thing does not work - I'll look into getting drive shafts with plunge joints instead.

I'm also going adjustable height using electric linear actuators to move the spring hanger up & down. This means that the wishbones are best off parallel. Non parallel or different lengths can be used to give you camber gain on compression which improves handling a bit. However if the height is adjustable, the camber would only be correct at one height.

Will. Interesting. I would have a look at a book called Chassis Engineering by Herb Adams. He's very non judgmental about different configurations, just gives the pros and cons of each. You can then make a pretty informed choice as to what path is likely to take you where you want to go.

Si

Bill and Si, the idea's come from a long line of thinking. The theory is to create an H - drive style vehicle and I started by thinking about a double wishbone type setup but running longitudinaly rather than transversly. The problem I saw with this was there were going to be a lot of joints (3 per corner) and, given the length of the arms (around 45 - 50") I was concerned that they would be quite heavy to make them stiff enough. Next I moved onto a semi torque tube setup with a load bearing lower link and a second upper link - simerlar to the idea used on the latest BMW motorbikes. However, where I've got to now seems to be about the lightest option as well as potentially the strongest. Given the length of the arms handling issues shouldn't be too major, but, yes, I see what your saying Bill. My hope is that a simerlar sort of control arm setup has worked on a very short wheel base vehicle which would, I hope, have excentuated any potential problems. Given the arms are running longitudinally I won't have the camber issues (which I can see would be a major problem) and I'm hoping I won't end up with too many scarey handling issues. I'd totally agree the Pinzgauer does suffer from a chronic lack of articulation but I only came to me as a comparison when I was writing the post - I was thinking about BMW's traditional motorbike setup.

Si, I'll certainly have a look at the book - I could do with a few new ideas especially with the chassis as I'm sure there's some major improvements that could be made over the designs I've got but I seem to be chasing my tail at the moment.

[simonr]

Ah! I remember now - we spoke of this.

If you can make it work (bevel drives etc) it could be pretty cool. Running the arms longitudinally gives you several advantages handling wise.

Si

[bill van snorkle]

Si thanks, your detailed description plus the photos has given me a better understanding of what you are up to. I understand your horses for courses approach but I also look forward to reading how it all works out in a variety of terrain conditions.

You have obviously given this a lot of serious thought and I hope it goes well for you.

Will, I wish you well also, but I'm sure that I am still missing something in your description. I'll tell you where I am having difficulties and you can correct any misconceptions.

If you are going to use LandRover swivel housings, and swivel balls, but only wish to use 2 constant velocity joints per corner, then your suspension becomes a swing axle design, with all the camber change and iffy handling this arrangement is famous for, because the Landy steering CV joint contained inside the swivel housing assembly cannot be employed to keep the wheels parallel with each other. To do that you would have to introduce a third CV joint inboard of the swivel ball flange, which aside from complicating things, also shortens the effective length of your driveshafts, thus limiting potential wheel travel. You could conceivably dispense with the swivel ball, just use the outer swivel housing with a ball joint bolted top and bottom attaching to your special longditudal radius arm. Then the suspension could be designed to keep the wheels parallel, but you would need some form f lateral control arm as well as I don't think CV's would be up to coping with compression loads.

To me, the mechanical complication of the''H'' drive transmission concept only makes sense when it is desired to have a sealed hull as in armored or amphibious vehicles. If you mount the left and right bevel boxes close together, side by side in the centre then they compromise ground clearance and cross axle rampover angle worse than a conventional offset differential. If you mount the bevel boxes further apart so that the hump is closer to the wheels for better clearance then this severely limits the length of your driveshafts which in turn dicates your wheel travel potential.

Bill.

Edit. Sorry Will, I think I have just grasped your concept. Correct me if I am wrong but I think you intend to integrate the driveshaft to each bevel box and the bevel box itself into the longditudal swing arm. I am not much into motorcycles, but re reading your reference to BMW reminded me that they employ shaft drive to the wheels.

If I'm finally on the right track forgive me for I am a knobhead.

[will_warne]

Si thanks, your detailed description plus the photos has given me a better understanding of what you are up to. I understand your horses for courses approach but I also look forward to reading how it all works out in a variety of terrain conditions.

You have obviously given this a lot of serious thought and I hope it goes well for you.

Will, I wish you well also, but I'm sure that I am still missing something in your description. I'll tell you where I am having difficulties and you can correct any misconceptions.

If you are going to use LandRover swivel housings, and swivel balls, but only wish to use 2 constant velocity joints per corner, then your suspension becomes a swing axle design, with all the camber change and iffy handling this arrangement is famous for, because the Landy steering CV joint contained inside the swivel housing assembly cannot be employed to keep the wheels parallel with each other. To do that you would have to introduce a third CV joint inboard of the swivel ball flange, which aside from complicating things, also shortens the effective length of your driveshafts, thus limiting potential wheel travel. You could conceivably dispense with the swivel ball, just use the outer swivel housing with a ball joint bolted top and bottom attaching to your special longditudal radius arm. Then the suspension could be designed to keep the wheels parallel, but you would need some form f lateral control arm as well as I don't think CV's would be up to coping with compression loads.

To me, the mechanical complication of the''H'' drive transmission concept only makes sense when it is desired to have a sealed hull as in armored or amphibious vehicles. If you mount the left and right bevel boxes close together, side by side in the centre then they compromise ground clearance and cross axle rampover angle worse than a conventional offset differential. If you mount the bevel boxes further apart so that the hump is closer to the wheels for better clearance then this severely limits the length of your driveshafts which in turn dicates your wheel travel potential.

Bill.

Edit. Sorry Will, I think I have just grasped your concept. Correct me if I am wrong but I think you intend to integrate the driveshaft to each bevel box and the bevel box itself into the longditudal swing arm. I am not much into motorcycles, but re reading your reference to BMW reminded me that they employ shaft drive to the wheels.

If I'm finally on the right track forgive me for I am a knobhead.

Bill, yes, that's the idea. You can see why I'm trying to shed weight where I can as it could all be very heavy.

[simonr]

So, Will....

Skid, Conventional or bendy in the middle steer?

Bill - that's kind of the point. It's an experiment. I've no more than a gut feeling about how it should perform and have only really found 3 people who have done anything similar. Having talked to them, I hope that I have designed around the major problems they experienced.

If it turns in to a disaster, I'll turn the axles in to 'poor-mans portals'. Turn each diff centre, shafts and uprights into a rigid beam axle but where the bottom of the diff is as high as it can be to max the clearance. There is at least one co in the US producing these.

Si

[will_warne]

So, Will....

Skid, Conventional or bendy in the middle steer?

Bill - that's kind of the point. It's an experiment. I've no more than a gut feeling about how it should perform and have only really found 3 people who have done anything similar. Having talked to them, I hope that I have designed around the major problems they experienced.

If it turns in to a disaster, I'll turn the axles in to 'poor-mans portals'. Turn each diff centre, shafts and uprights into a rigid beam axle but where the bottom of the diff is as high as it can be to max the clearance. There is at least one co in the US producing these.

Si

Well..... 4 wheel conventional steer plus skid steer as it'll be easy to setup. I think this may be the biggest issue with the design - to stop it being massively wide I'm going to have to limit lock and the cabin is going to be cosy to say the least!

I'm yet to try and find a solution to the SVA problem as I do want to SVA it and trying to sort a mechanical steering linkage for the front wheels will end up with something totally Heath Robinson. Full hydro would be so much simpler!

[simonr]

I'm yet to try and find a solution to the SVA problem as I do want to SVA it and trying to sort a mechanical steering linkage for the front wheels will end up with something totally Heath Robinson. Full hydro would be so much simpler!

OK, what about putting a small steering box on each arm (Suzuki Vitara for example), drilled for hydro-assist. Then the linkages do not have to take too much torque. You add a few bore bevel drives on a transverse steering 'axle' with another bevel drive to the steering wheel.

You can buy nice ready made bevel drive gearboxes from HPC.

Hope your cheque book is thick!

I think you might be better off with bendy in the middle steering and register it as a dump truck?

Si

[will_warne]

OK, what about putting a small steering box on each arm (Suzuki Vitara for example), drilled for hydro-assist. Then the linkages do not have to take too much torque. You add a few bore bevel drives on a transverse steering 'axle' with another bevel drive to the steering wheel.

You can buy nice ready made bevel drive gearboxes from HPC.

Hope your cheque book is thick!

I think you might be better off with bendy in the middle steering and register it as a dump truck?

Si

Si, that's a nice idea with the steering boxes - I might have to look at that!

Hmmm, yeah, this is going to be an expensive project but I've resigned myself to that. I knew with the bevel boxes I'd have to have them made. I played about with the idea of using heavily moddified diffs with solid centres but the gearing won't allow me to do it. A few days ago I think I may have also found a solution that might mean I can get away from bevel boxes which'd be lighter and cheaper (everythings relitive, though ). I'm just waiting to hear back from the manufactures to see if they think they can make something that'll be up to the job. I'm quite hopeful as they've done quite a lot of work with Baja teams so know the sort of abuse they'll have to stand up to.

I have thought about bendy middle but I'm planning to use the vehicle abraod a fair bit so it'll have to be able to do speed sections. The couple of times I've driven dump trucks I've not been convinced they'd be nice to drive quickly!

[Steve Hiatt]

That is very interesting Steve. Would you happen to have any pics of your front end layout ? If you are using 110 outer assemblies would I be correct in thinking that your front end has three constant velocity joints on each side, instead of the traditional two per side of conventional independantly suspended front wheel drive systems?

Bill.

Been busy racing it today, but I'll take some pics in the week. Essentialy it's LR stub axle and hub with 110 CV. The whole is mounted on a fabricated upright. The inner CV is BMW/Porsche 930. There is no third joint.

[honitonhobbit]

As a further to Jules's thread, I used to race a rail. Indi supension - obviously with 2 wheel drive. Back in the good old days of the AWDC rails were almost alwasy the ones to beat. Light, low(ish) power, high gearing but on the right course (anything except Sidbury in the wet) alomost unstopable. Drive train breakages were rare even when we went up to the Lancia Volumex lump and the renault transaxle. Fifteen inches of travel at the rear was okay, with thirty three at the front using a modded beetle system blatantly copied form a Baja bug. The Renault TA had an LSD but we ran with fiddles as well for added cornering/traction.

When our main sponsor threw in the towel we were looking at a Subaru t box/gearbox with custom made CV's and shafts from the states, that would have given us twenty inches all round with air assistance for full compression - 25 year old technology

[bill van snorkle]

Si, there is a stability issue with bendy articulated steering on vehicles with only 2 axles. The best way I can describe it is to imagine the vehicle attempting a U turn on a down slope, even a not very steep one. All the vehicle mass between the front and rear axles is now hanging out there unsupported on the downhill side and flops over. The US army tried to make large offroad cargo trucks from articulated earth movers(scrapers) and found this glaring deficiency during field trials.

bill.

[simonr]

I found similar driving a dump truck!

Si

[bill van snorkle]

Si, that's a nice idea with the steering boxes - I might have to look at that!

Hmmm, yeah, this is going to be an expensive project but I've resigned myself to that. I knew with the bevel boxes I'd have to have them made. I played about with the idea of using heavily moddified diffs with solid centres but the gearing won't allow me to do it. A few days ago I think I may have also found a solution that might mean I can get away from bevel boxes which'd be lighter and cheaper (everythings relitive, though ). I'm just waiting to hear back from the manufactures to see if they think they can make something that'll be up to the job. I'm quite hopeful as they've done quite a lot of work with Baja teams so know the sort of abuse they'll have to stand up to.

I have thought about bendy middle but I'm planning to use the vehicle abraod a fair bit so it'll have to be able to do speed sections. The couple of times I've driven dump trucks I've not been convinced they'd be nice to drive quickly!

Will, Couldn't you buy an old Ferret to source the major components from and keep the costs down ?

I think it was Berliet in France in the late 1920's that built a small production run of 4 and 6 wheel drive officers cars that had a similar drive layout to what your planning. One of the Observers Book of Military Vehicles up to 1940 in the French section shows a photo of one crossing a hummock with an amazing amount of wheel travel. I recall some of the text that said they employed long cantilever leaf springs as the suspension medium.

Bill.

[will_warne]

Will, Couldn't you buy an old Ferret to source the major components from and keep the costs down ?

I think it was Berliet in France in the late 1920's that built a small production run of 4 and 6 wheel drive officers cars that had a similar drive layout to what your planning. One of the Observers Book of Military Vehicles up to 1940 in the French section shows a photo of one crossing a hummock with an amazing amount of wheel travel. I recall some of the text that said they employed long cantilever leaf springs as the suspension medium.

Bill.

Interesting, I'll have to keep an eye out for photos.

I've thought about Ferret parts and I may end up using some. Luckily I've got a friend with 2 so its fairly easy to get measurements. I think he may also have a spare bevel box which I could have a play with...

[Corrode Finger]

Cracking continuation of my initial thread question.

Anyone got any pics that explain the ideas being discussed, just to assist those like myself, and come upto speed and follow some of the ideas.

[bill van snorkle]

Cracking continuation of my initial thread question.

Anyone got any pics that explain the ideas being discussed, just to assist those like myself, and come upto speed and follow some of the ideas.

You know, in all the years I have been interested in and messed around with offroad vehicles, I don't recall ever seeing an actual photo of the type of suspension we are currently discussing, or eventhe inner workings of a Ferret scout car for that matter, but surely photos exist somewhere.

I just remembered another French truck builder of the 1930's that built 4x4 and 6x6 trucks with independant suspension and individual driveshafts to each wheel, and that company was Laffly. I'll try a google search in a tick and seewhat comes up.

Bill.

Edit. I tried the google search thing on both Berliet and Laffly. it's very hard going, a few photos of the Laffly 6x6's came up but almost zero tech. Nothing on the 1920's era 6x6 Berliet car. If anyone has a copy of the Observers book on Military Vehicles up to 1940 by Bart H Vanderveen it would be nice to see the photos of those trucks again. My copy of that book has disintegrated to dust from old age and overuse.

Bill.

[will_warne]

Cracking continuation of my initial thread question.

Anyone got any pics that explain the ideas being discussed, just to assist those like myself, and come upto speed and follow some of the ideas.

Paul, its a bit like this only differant

Imagine an H with each of the 4 vertical parts of the H pivoting in and out of the page at the bar across the letter. Put a wheel at the ends of these ams and dive them drive and that's the basic principal. I've got a load of sketchs but no scanner otherwise I'd ping a couple up