Split wishbone suspension

Go here for info on chassis construction, body work and suspensions

Split wishbone suspension

Postby David on Sun Oct 19, 2003 8:50 am

I am looking at building an a bucket using a 30 a model cowl and doors rat rod style and I wanted to use split wishbones in it for the front, does any body know what the rules for these are in queensland on lh9 rego?
I am trying to build my first rod cheaply so any info would be greatly appreciated.
Dave.
David
 

Postby GBS on Sun Oct 19, 2003 11:26 am

Dave

Split wishbones have been used for as long as there have been rods but that does not mean they are a good idea. The problem is they cause massive binding in the suspension.

When you split them you are left with the front end of the rods bolted solidly to the axle. As the wheel follows the contours of the road and moves up and down, the front end of the split rod naturally moves with it. Being a solid rod the rear end also wants to go up and down the same amount but it canít because you have it mounted solidly to the chassis. Something has to give and it is the axle. It twists as the suspension moves.

An I beam will twist which is bad enough but a tubular axle wonít which is even worse. No matter which type of axle you use you are going to have binding in the suspension. Broken chassis mounting brackets are also common with split rods.

The other type of split rod is the hair pin style. Rod magazines often talk favorably about hair pin rods calling them ìtraditionalî and giving the impression they are desirable but they are just as bad as split originals.

The only successful way to locate a beam axle is the way Ford did it. If the design of your car prevents you doing it this way then use four bars. They are still a compromise but are about 1000% better than split rods.

I am not sure about Qld rego rules. Ring Jan Evans, National Secretary of the ASRF, in Brisbane on 07 5564 0632 and she should be able to put you on to someone who can advise you.

Brian
GBS
Senior Member
 
Posts: 1319
Joined: Sun May 18, 2003 10:10 pm
Location: Central Coast NSW

Postby Brett.C on Mon Oct 20, 2003 5:44 pm

Have any of you guys seen the way Nissan and Rover mount live axles in the front of their 4WDs?
They use what amounts to short split radius rods, which are attached to the axle using compliant bushes. Also just tonite I was following a jacked up Suzuki Sierra. It seemed to have a similar setup on the rear end.

I've often thought that a similar setup could be used on a rod. The bushes wouldn't need to be too big and ugly due to the long length of the Ford's radius rods and the rather limited suspension travel involved. Neoprene Holden shackle rubbers maybe? The Suzi's setup looked reasonably compact. If you were to look at the axle in cross section it had one bush in the 6 o'clock position and another in the 3 o'clock position. By the amount that this thing was rolling about the road it would cope in a rod no worries.

I also think that the inherent springiness of these bushes would aid roll stiffness if employed with a tube axle.

One thing that would need to be considered first is the leverage forces that would be applied by a dropped axle. But then again the huge tyres, weight and high centre of gravity on these 4WDs would also result in some pretty large lever forces.

Anyway, just an :idea: .
Brett.C
Old Hand
 
Posts: 4266
Joined: Tue Feb 04, 2003 3:27 pm

Postby GBS on Tue Oct 21, 2003 10:43 pm

Brett

I have seen those rods on the four wheel drives. I would say the binding is obviously eliminated by the large rubber bushes. The short control arms on the Jaguar rear ends probably work the same way. They also have large rubber bushes.

I doubt if this set up would work on a rod without looking ugly. Imagine large bushes holding the rod onto an I beam. The design of these bushes also presents a problem because as sure as can be there would be more to their design than meets the eye. I would imagine they would be have a variable compression rate of some kind in a similar way to the way a tapered suspension bump stop rubber acts as a variable rate spring when
the suspension bottoms out.

I think it is in the too hard basket for me at this stage but it would be a good question for Ted Robinette if he is listening.

Brian
GBS
Senior Member
 
Posts: 1319
Joined: Sun May 18, 2003 10:10 pm
Location: Central Coast NSW

Postby Brett.C on Wed Oct 22, 2003 4:46 pm

Brian,
I thought too that this would be too big n ugly until I saw the Suzuki. It had quite small bushes with relatively short arms and lots of suspension travel. I figured then that a similar setup would work well on a rod with much longer arms and much less wheel travel. I'm thinking of a bracket no larger than a four bar's batwing but a bit wider to accommodate the bushes.
As I said just an :idea:

Another :idea: I've been toying with for a long time is a setup like this for a track style roadster.
Image
The axles wouldn't have any drop and would be mounted above the chassis rails. This would get the thing down real low and the straight axles would give it a vintage racecar look. Of course each axle would have to be kinked slightly to align the wheels. The radius rods would be Ford of course and they would be attached to the axles in the time honored fashion. Steering would be Camira rack or similar. A real cool thing would be to mount the c/overs inboard so they can't be seen
I put this design to an engineer many years ago and he could see no probs with it.

I love the look of split radius rods and for many years I've been racking my brain thinking of ways to keep them on a rod without the disadvantages. I've even thought up a double wishbone independent that uses them as castor rods. It would have a trad look from the side and hi tech look from the front. :?
Brett.C
Old Hand
 
Posts: 4266
Joined: Tue Feb 04, 2003 3:27 pm

Postby Brootal on Wed Oct 22, 2003 6:42 pm

GBS wrote:Brett

I doubt if this set up would work on a rod without looking ugly.
Brian


Doesn't seem to have stopped all those people using Holden front ends.

...did I just say that out loud??? :D
It's OK, I'm not really from Sydney, I just moved there, but now I'm back in Perth so I'm normal again.

Ramblers, Hot Rods, Surfing and Model Cars
User avatar
Brootal
Old Hand
 
Posts: 2862
Joined: Tue Jun 11, 2002 7:04 pm
Location: Trigg, Western Australia

Postby PeterR on Wed Oct 22, 2003 8:00 pm

bcal,
The suspension configuration you have drawn has been used on Ford F series pickups and small trucks for over thirty years. Their name for it is "Twin I Beam".

It is cheap to manufacture, strong and durable. However compared to the Chev C series with conventional upper and lower A arms these vehicles are a dog to drive for a number of reasons: -

The wheels go through large camber changes due to the relatively short length of the axle.

The tyre/pavement contact patch moves sideways when negotiating bumps because of the height of the pivot point.

The toe-in changes during bumps because the tie rods and axles do not have coincident pivots. This is particularly so on the 250 and 350 with one piece tie rods.


You could reduce these effects by: -

lengthening the axles by taking the pivot points outside the rails, so they are just inboard of the opposite radius arm -but that would look terrible.

lowering the pivot points as Mercedes did on the swing axle sedans but this would also mean lowering the steering.

arranging the tie rod length and pivot points to minimise bump steer but this is difficult particularly if you wish to use rack and pinion.

Another tack entirely would be to fabricate a two piece tube axle that has a sleeve joiner in the middle so the axle can twist freely but still has full beam strength. Check out the deDion rear on a Rover.
PeterR
 

Postby GBS on Wed Oct 22, 2003 8:55 pm

Brett

There is that track roadster mentioned again, you are going to have to build it.

I will have to find a Suzi and have a look but I donít think I will like it. Even a bat wing with the current tiny bushes looks too big and cluttered to me. I like an unsplit original.

I was just about to say your drawing looks like a Ford twin I beam but Peter beat be to it.

Another suspension that comes to mind when looking at your drawing is the Hilman Imp. It used a V shaped lower control arm pivoting from the centre line of the car. There was a small piece of beam axle with a king pin on the end. Suspension was by coil overs.

You could use that system on a track roadster but you would not have a radius rod down the side.

You see this suspension these days on some makes of golf buggies and some people might say that is where it belongs. I must admit the Imps were a strange looking sight sliding down through the esses at Bathurst in the 1960s. The front wheels looked like the rear of a swing axle VW. From memory the racing Fraser Imps in England did go well though. Not sure what they did to the front ends.

I suppose that suspension is somewhat similar to the spilt I beam of an Allard but I can not remember how the Allard had its radius rod mounted.

I suppose if we keep getting all of these ideas, one day we will finally come up with the ultimate rod suspension.

Brian
GBS
Senior Member
 
Posts: 1319
Joined: Sun May 18, 2003 10:10 pm
Location: Central Coast NSW

Postby Brett.C on Wed Oct 22, 2003 10:51 pm

The suspension configuration you have drawn has been used on Ford F series pickups and small trucks for over thirty years. Their name for it is "Twin I Beam".

Yes I'm aware of the twin I beam Fords but I originally got the idea from a pommy sports car but for the life I can't remember which one :?
The original Lotus clubman keeps coming to mind, however I doubt if this was it.

Personally, because I'm fully aware of it's drawbacks, I'd never use a setup like this. One thing that wasn't mentioned was the incredible amount of upsprung weight involved. That in it self would be enough to discount it.

Once you've designed and built your own IFS and you realise how easy and straightforward it really is and how well they perform, anything else is a compromise.

Now if only you could design an IFS that looks good in a fenderless rod?
These are my humble effort so far:
Long 2" OD tubular lower control arms attached to torsion bars (similar to Morris Marina).
Split radius rods acting as castor rods.
Chrome the arms and the rods so that they stand out.
Cortina or similar stub axles. (nice and compact)
Tubular upper A arms attached to cantilevered inboard shocks. Painted body colour to blend in.
Large dinner plate sized headlights to help hide the upper arms.

Another tack entirely would be to fabricate a two piece tube axle that has a sleeve joiner in the middle so the axle can twist freely but still has full beam strength. Check out the de Dion rear on a Rover.


Peter, I looked these up after you referred to them a while ago. A very interesting setup that needs to be explored further. However, didn't they use a spline on the de Dion tube to allow it to change track width with suspension travel? This would not allow the axle to swivel, which is what you'd want on a solid axle with split rods. Good concept tho.
BTW good to see you're still lurking around mate :)

I suppose if we keep getting all of these ideas, one day we will finally come up with the ultimate rod suspension.

I'll leave you with a quote from a famous French inventor, aviator philosopher and poet.

One many may hit the mark, another blunder; but heed not these distinctions. Only from the alliance of the one, working with and through the other, are great things born.
Antoine de Saint-Exupery 1900-1944
Brett.C
Old Hand
 
Posts: 4266
Joined: Tue Feb 04, 2003 3:27 pm

Postby david on Sat Oct 25, 2003 6:14 am

Thanks for all the info. I dont think I'll go with split wishbones. I think if i was going to go ifs I'd use a arms from a lotus 7 replica that uses cortina stubs as apparently hq discs bolt strait to them.

I cant really picture the 4wd suspension, I'll have to go and stick my head under one of the 4wd's mentioned to get an idea.

I have seen one rod using split wishbones to mount the axle but with torsion bars inside the chassis rails instead of a spring, I'm not too sure if this would make any difference but it looked really good.
thanks again.
Dave.
david
 

Postby Brett.C on Mon Oct 27, 2003 6:28 pm

cortina stubs as apparently hq discs bolt strait to them

Thanx David I wasn't aware of this.

Torsion bars wouldn't do anything to eliminate the problems associated with split radius rods. When used on a beam axle you need lever arms to transmit the load from the axle to the bars. Spring rates can be adjusted by varying the effective length of these arms. Also ride height can be adjusted by either setting the spines in different locations in their sockets or thu bolt adjusters similar to what's used on jap utes.
Very useful set up torsion bars but they do need a panhard rod on a solid axle.

I have a couple of sets of torsion bars from Alfas lying around in the shed. I also have a set of Cortina stubs but the only problem with them is that they're front steer and so the ackerman thing is all wrong for a rear steer rod. Recently I was looking at the frontend set up on a Jowett Jupiter (now how's that for left of center!). The Jupiter had a tubular chassis, which was basically two pieces of parallel pipe. The F/E was a double wishbone setup with torsion bars and rack and pinion. Looked very neat, but with only 900 ever built the chances of obtaining one are zilch. However a close approximation could be built out of various bits n pieces.

Peugeot 403 frontends are worth a look. They had a transverse leaf spring that doubled as the lower control arms. The upper arms are quite neat and they are pivoted from piston dampers that acted as the shock absorbers. The cast iron crossmember is way too ugly but a new unit similar to a Ford crossmember can be easily fabbed. The Peugeot dampers could then be attached to this or new pivots made up and telescopic shocks used instead.
But there are two possible problems that I see with this F/E.
Firstly.
I cannot see that there would be a definitive point at which the spring/control arms pivots. This would therefore make it difficult to determine the correct location of the steering rack's inner pivots, tho Peugeot's location could be copied.
Secondly.
Under heavy braking I see the spring twisting and deflecting backwards. This would have the effect of shifting the castor in the negative direction, which is the opposite of what you want under these circumstances.

Still anything has got to be better than shelling out 3-4 grand on a beam and 4bar IMO :wink:
Brett.C
Old Hand
 
Posts: 4266
Joined: Tue Feb 04, 2003 3:27 pm

Postby Brootal on Mon Oct 27, 2003 7:20 pm

bcal wrote: Peugeot 403 frontends are worth a look. They had a transverse leaf spring that doubled as the lower control arms. The upper arms are quite neat and they are pivoted from piston dampers that acted as the shock absorbers...


Stewart Campbell's roadster uses that kind of front end I think bcal. I know he said it was a '55 Peugeot. Unfortunately I don't have a close up pic of the front end, but I do have a shot of the car and there sure as shit ain't nothing wrong with the way it looks. :)

Image

I've also been in the car at 90+ MPH (Shhh... don't tell anyone) and it handles, stops and steers very well. Not sure how much modifying Stewie did, but I'm pretty sure it's not exactly a bolt in!
It's OK, I'm not really from Sydney, I just moved there, but now I'm back in Perth so I'm normal again.

Ramblers, Hot Rods, Surfing and Model Cars
User avatar
Brootal
Old Hand
 
Posts: 2862
Joined: Tue Jun 11, 2002 7:04 pm
Location: Trigg, Western Australia

Postby Brett.C on Mon Oct 27, 2003 9:06 pm

Brootal.

I had a look at Stewarts car when he was building it about 12 years ago. From what I recall it was fairly extensively modified. The X member had been ditched in favour of a unit fabbed from mild steel. The dampers were replaced with adjustable pivots for caster and camber adjustments and tele shocks used. I also recall the Peugeot rack was replaced with a steering box. I think the Peugeot originally had a front mounted rack tho I could be wrong. Also the frame was stepped to get it down low enough and still retain spring travel.
Unfortunately I haven't seen the car since it was completed.

There was another rod in the Newcastle area with a similar setup and it predates Stewart's car. I worked on a project with the guy that had built it and I think it was a 32 roadster. He reckoned it rode and handled real well. Never saw the car and have not heard of its whereabouts. At the time I was using the same engineer that he had used and he was also impressed with it.

They're not a bad lookin setup for an open rod and they have an early Ford look about them. I'm surprised that there aren't more around but I spose coz they're definitely not a bolt in fit most guys are put off.
Brett.C
Old Hand
 
Posts: 4266
Joined: Tue Feb 04, 2003 3:27 pm

Postby GBS on Tue Oct 28, 2003 10:32 pm

I have often wondered why we have not seen more Peugeot front ends on rods, particularly after Stewartís car hit the road. It really looks good and it sounds like it also performs well.

I think Larry OíToole missed a good opportunity when he did a full feature on Stewartís roadster in issue 105. He skipped over the suspension in a couple of lines. It could have been the subject of a feature on its own.

If you read books on the various types of suspensions that have been used over the years, this design comes in for its fair share of criticism but I think you would have to be driving right on the ragged edge to notice its shortcomings. I drove plenty of 203 and 403 models back in the sixties and I thought they were fine. I would be more than happy if my rod handled as well as they did.

I have a photo of a 203 ute taken from underneath as it sat on the top of a pole in outback NSW. (Donít ask how or why and I did not take the photo.) The steering rack is front mounted. The pivots on the end of the rack look like they are in line with the upper inner bushes.

Plenty of these cars were sold after their incredible success in the 1953,í54 and '55 Redex trials so there should still be a few around. They are well worth a look.

Brian
GBS
Senior Member
 
Posts: 1319
Joined: Sun May 18, 2003 10:10 pm
Location: Central Coast NSW

Postby David on Sat Nov 01, 2003 6:40 am

Thanks for all the info.
Does any one have a photo of the front of stewarts roadster or more info on this type of front end? this sounds interesting to me.
I wonder what you would have to do brake wise with this type of front end?

I am starting to look at the costs involved and I am thinking that it might be better to wait a little longer and build a proper roadster like I really want with full rego.
thanks again.
Dave.
David
 

Next

Return to Construction

Who is online

Users browsing this forum: nz jailbar and 3 guests