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Very interesting suspension design
derf - 13/10/05 at 02:44 PM

Small disscussion on locostusa.com:

http://www.locostusa.com/forums/viewtopic.php?t=144

I happened apon this a few minutes ago, and was very interested in it. very low shock design, pushrod, mumford linkage.

The first and second pics are digital renderings, but the third one is shown on an older mustang II







[Edited on 13/10/05 by derf]


smart51 - 13/10/05 at 02:51 PM

Horizontal dampers are usually a problem. Citroen managed to make it work in the eighties. Rover engineers tried but failed to copy it. It's a good idea for space saving, lowering C of G and increasing luggage space. If you can make it work.


britishtrident - 13/10/05 at 03:16 PM

The Watts linkage is good but the rest I suspect is trying to be much too clever without any real gain.


britishtrident - 13/10/05 at 03:17 PM

[Edited on 13/10/05 by britishtrident]


derf - 13/10/05 at 03:38 PM

Yes it's an excellent design, and would definatly fit in with the design of the locost frame. Since I saw it, and I am going to re-do my front suspension. I have been contemplating re-doing my rear suspension along the lines of what is shown here. The way that it sits would definatly fit in the chassis, and would also give a hight adjustability into my rear.

The only modification to the design is to get rid of the 3rd center link, and add a second set of trailing arms above the ones that are there.

Can anyone take a guess if the watts link will fit below the chassis?


gustavo_brum - 13/10/05 at 03:41 PM

That Mustang owner really went through a lot of cutting and welding to make a chevette rear suspension... Three-link suspension like this one (and the chevette) are pretty good for turning, although not much better than the locostīs 4 link. I agree the watts linkage is the only original thing there, the rest is just useful to impress your friends, but no better in the performance department, and heavier too.


Bluemoon - 13/10/05 at 04:34 PM

Spot the two bolts in shear, and there holding all the weight of the car? I would'nt wan't is like that, it's not going to last long.

Dan


MikeR - 13/10/05 at 04:51 PM

Dan, look at the suspension mounts on most vans - all the ones i've seen in the traffic light queue have them mounted in single sheer. Its not the best practice but is ok if engineered correctly.


Syd Bridge - 13/10/05 at 05:01 PM

What's wrong with the standard damper arrangement?

And a sensible Watts Link has the crank attached to the chassis. Unsprung weight and all that. Only a seppo could dream up that nightmare.


The most interesting thing is those mufflers/silencers. By the look of the weld print through, they are Flowmasters, and date back to the mid eighties in design. But, are very effective and create little back pressure.

They'd have to be the most sensible part of the whole car, and would do more for the total performance than that abomination of a rear suspension setup.

[Edited on 13/10/05 by Syd Bridge]


gazza285 - 13/10/05 at 05:38 PM

Different angle.


It doesn't work correctly. The fixed arm means the axle will just pivot around the front mount and put unnecessary loads on the pinion and propshaft. Nice use of different coloured paints, but other than that it's bullshit baffles brains thinking.


Edit.
The more I look at it the more it upsets me. Just looking at the crank arms and it doesn't take much to figure that the rate will fall fairly dramatically. Daft thing is that with the pushrod mount being so low on the axle that there is room to put a vertical shocker unit anyway.

[Edited on 13/10/05 by gazza285]


millenniumtree - 13/10/05 at 05:57 PM

Why the hell didn't they just do dual trailing arms AND the horizontal dampers?

That inane center arm would cause the whole rear axle to twist in relation to the propshaft.

It's fine if you don't actually expect the axle to move.


Peteff - 13/10/05 at 06:15 PM

I can't see what locates the top of the axle at the wheel ends. It looks like it will pivot forwards. I don't think changing things for the sake of it does anyone any good. The Watts linkage is a proven method of locating axles as is panhard and mumford links but all that is doing is complicating something for no gain.


quattromike - 14/10/05 at 12:35 PM

quote:
Originally posted by Syd Bridge

The most interesting thing is those mufflers/silencers. By the look of the weld print through, they are Flowmasters, and date back to the mid eighties in design. But, are very effective and create little back pressure.

They'd have to be the most sensible part of the whole car, and would do more for the total performance than that abomination of a rear suspension setup.

[Edited on 13/10/05 by Syd Bridge]


Is it just me or does the exhaust just exit right underneath the car? That'll be a bit fumie at the traffic lights

Mike

[Edited on 14/10/05 by quattromike]


chrisf - 14/10/05 at 01:08 PM

quote:

I don't think changing things for the sake of it does anyone any good.



I agree. It seems a better solution for using inboard dampers is to use the traditional locost-style rear suspension with a pan hard bar. If you want the inboard suspension, just weld on the drop links and connect them to the rockers.

But consider this: how strong is your chassis after the rear bulkhead? Can it take the lateral loads of the dampers? On a live axle chassis, there isn't much structure after the rear bulkhead. It's main purpose is to provide a fuel tank location and provide the frame for the rear ali panel. I suspect that when damper loads are placed through the rearmost part of the chassis (assuming no additional bracing is done), a pretzel will result.

FWIW, the pictured design uses a falling rate suspension. I question the person that goes throught the trouble of modeling it all up--then designing in a falling rate suspension. Seems worthless.

--Just an opinion, Chris

PS. A lot of American muscle cars dump their exhaust under the car. I don't really know why, but it doesn't seem to cause that much trouble. It is illegal in most states, though.


Dale - 14/10/05 at 02:44 PM

Running a watts link horizontal like that would put the rear roll center at the center pivot point?
I would like to find some info on mumford link design but it seems to like the black box in programing that says "miracle happens here"
Dale


MikeRJ - 14/10/05 at 09:19 PM

Hmm, all this work...and it's still a live axle. Effort better expended on a good IRS design IMO.

Didn't Lotus have a series of axle housing failures with their original three link design? Forces from accelerating and braking put torsional forces through the axle tubes which aren't there with a 4 link setup.


Bob C - 14/10/05 at 09:56 PM

I think some posters have missed the point - the pictured suspension is grafted onto the underside of an existing car that looks like it had cart springs. With some ingenuity they've improved the axle location a million percent within the space constraints and made a nice looking job of it.
You'd be insane to put it on a locost though . . . . .
cheers
Bob


Bob C - 14/10/05 at 10:29 PM

oh yeah...

"I don't think changing things for the sake of it does anyone any good."

I change things for the sake of it whenever I get a chance..... I happen to think it's how progress happens!!
So who wants a go in my car when it's done ? ? ? ?
ttfn
Bob


gazza285 - 14/10/05 at 10:55 PM

quote:
Originally posted by Bob C
I think some posters have missed the point - the pictured suspension is grafted onto the underside of an existing car that looks like it had cart springs. With some ingenuity they've improved the axle location a million percent within the space constraints and made a nice looking job of it.
You'd be insane to put it on a locost though . . . . .
cheers
Bob


I'm afraid not. What they have done is added loads of weight, made the axle rotate around the forward pivot, reduce the efficiency of the springs/shock absorbers, and made a nice job of it.

Just about every live axle racing/rally car had four trailing arm and either a Watts linkage or Panhard rod coupled with vertical coil overs.

This was not by chance.

One simple question, how is this better than the standard Locost rear end and why.


Peteff - 14/10/05 at 11:06 PM

Then it's called improving it, not changing it, and is a completely different matter. If that is replacing a cart spring rear then it's probably an improvement. I agree that he would have been better off with another set of trailing arms instead of the contraption bolted to the diff though. edit:- I've just looked again and he could have mounted the shocks upright from the bolts that the bellcranks pivot on and saved even more time, weight and effort and probably be more efficient.

[Edited on 14/10/05 by Peteff]


Peteff - 14/10/05 at 11:33 PM

Here's a picture of a mumford link setup Dale.


There's a bit about it on the site as well here


Bob C - 14/10/05 at 11:53 PM

hi gazza,
I think you missed my point - it's not in a locost is it? The installation photo shows you can't put the upper trailing arms in so the chevette/ascona/manta style system has been used. Quite right, it's not better than a std. locost system but it's not in a std. locost etc. etc.
FWIW I agree it would be simpler lighter & probably better with vertical dampers & it looks like there's room. There's plenty not to like, rod ends holding whole weight of car stuck out 3" on a bolt & spacer, questionable triangulation of the back face of the 'box' - at least the bellcranks on the photo look sturdier than the rendered ones (gorgeous rendered images though!).
night night
Bob


Rorty - 15/10/05 at 01:50 AM

I've looked at the pictures (agreed, nice renderings) over and over again and the only answer I can come up with is "because he could"!
It's not progress, it's overkill, it's 'king ugly, it doesn't appear sturdy or safe and it doesn't look like it would actually work very well, if at all.
But, if I had his brain in my head and the same amount of spare time and cash, I would probably have done the same thing.


cymtriks - 15/10/05 at 11:04 AM

quote:
Originally posted by gazza285
Different angle.


It doesn't work correctly. The fixed arm means the axle will just pivot around the front mount and put unnecessary loads on the pinion and propshaft.


Not quite!

The central arm has a floating link at the front so it cannot locate the axle fore-aft.

What it does do is to stop the axle from rotating. The two trailing links provide fore-aft location, a third, or fourth trailing link to prevent the axle from rotating isn't needed as this movement is prevented by the third central link.

The complete set up goes like this:

Translation:
fore-aft by the two side links
sideways by the Watts linkage
vertical by the springs

Rotation:
About car centre line by the springs
About Axle centre line by the trailing link and the central floating link
About the vertical by the trailing links

That's all six taken care of and not conflicting so it does work!

Having said that how many links are there?

2 pushrods
2 bell cranks
2 trailing links
2 lateral links
1 Watts link centre
1 trailing arm
1 trailing arm vertical support at the front

That's 11 links!

What on Earth's wrong with a Satchell link? Just four links, two upper trailing and two lower angled from the ends of the axles to the back of the transmission tunnel. All for links being rubber bushed or spherical jointed. Simple. Cheap. Works well.


britishtrident - 15/10/05 at 02:19 PM

quote:
Originally posted by Syd Bridge
What's wrong with the standard damper arrangement?

And a sensible Watts Link has the crank attached to the chassis. Unsprung weight and all that. Only a seppo could dream up that nightmare.

snip
snip
[Edited on 13/10/05 by Syd Bridge]


Actually in the real world nearly all Watts linkages have the crank mounted on the axle, most follow the Ford "zero steer" axle location first seen on works Mk1 Escorts circa 1972, the same arangement was used by Spen Wilks (seppo ?) on the rear of the Rover Sd1 --- main reason for mounting the bell crank on the axle is it is difficult to mount a pivot on fresh air --- the increase in unsprung weight is tiny in comparision to the live axle weight.

Of course it dosen't alter the fact the suspension design under consideration is flawed and way over complex for no reason.



[Edited on 15/10/05 by britishtrident]


britishtrident - 15/10/05 at 02:32 PM

quote:
Originally posted by MikeRJ
Hmm, all this work...and it's still a live axle. Effort better expended on a good IRS design IMO.

Didn't Lotus have a series of axle housing failures with their original three link design? Forces from accelerating and braking put torsional forces through the axle tubes which aren't there with a 4 link setup.


Lotus & Caterham were prone to tearing the mounts out the rear axle case -- the actual torsional forces on axle aren't less than in the Locost aranagement but on the 5 link Locost system are fed into the axle in a more sensible way. The Problem with the arangement on the early 7 and Mk1 Lotus Cortina was the loads were being fed in to one point on a paper thin axle casing.

As I think somebody else in the thread has pointed out you can get the same roll centre location by using 4 links with angled lower links --- think Cortina Mk3+ axle turned
upside down.



[Edited on 15/10/05 by britishtrident]


gazza285 - 15/10/05 at 03:59 PM

quote:
Originally posted by cymtriks
quote:
Originally posted by gazza285
Different angle.


It doesn't work correctly. The fixed arm means the axle will just pivot around the front mount and put unnecessary loads on the pinion and propshaft.


Not quite!

The central arm has a floating link at the front so it cannot locate the axle fore-aft.

What it does do is to stop the axle from rotating. The two trailing links provide fore-aft location, a third, or fourth trailing link to prevent the axle from rotating isn't needed as this movement is prevented by the third central link.

The complete set up goes like this:

Translation:
fore-aft by the two side links
sideways by the Watts linkage
vertical by the springs

Rotation:
About car centre line by the springs
About Axle centre line by the trailing link and the central floating link
About the vertical by the trailing links

That's all six taken care of and not conflicting so it does work!

Having said that how many links are there?

2 pushrods
2 bell cranks
2 trailing links
2 lateral links
1 Watts link centre
1 trailing arm
1 trailing arm vertical support at the front

That's 11 links!

What on Earth's wrong with a Satchell link? Just four links, two upper trailing and two lower angled from the ends of the axles to the back of the transmission tunnel. All for links being rubber bushed or spherical jointed. Simple. Cheap. Works well.




Explain to me how it keeps the axle from rotating. When you move the axle up or down this arm is fixed to the axle casing and moves up and down accordingly. The vertical movement is prevented at the front by the link arrangement so if the axle moves up and down it must also be rotating around the front mount.Yes it is preventing the axle twisting under drive and braking but it is forcing the axle to rotate under bump.


cymtriks - 16/10/05 at 07:11 AM

I ment that it prevents free rotation.

The central link could be described as a torque reation link, it transmits no fore-aft loads at all but is loaded in bending as it as it takes up the torque reaction.

I still reckon Satchel link would be better though it would be hard to get the right angles for the lower tubes in the available space. Perhaps an axle mount swept back from the axle centre line would be needed, or a stronger lower tube, say 1/8 wall thickness.

Has anyone tried a Satchel link?


Dale - 16/10/05 at 02:55 PM

On the mumford pic shown. Am I correct in that the roll center is the joing point of the 2 long arms if their lines where extened to meet in the middle.?
Dale


Syd Bridge - 16/10/05 at 04:26 PM

quote:
Originally posted by britishtrident

Actually in the real world nearly all Watts linkages have the crank mounted on the axle,
[Edited on 15/10/05 by britishtrident]

What's cheap to build on a production line is not necessarily ideal for a racecar. (Otherwise we would all still be driving rwd front engined cars.)

Haven't lately looked under the rear of an Aussie V8 racecar, and more than a few nascar type things, have you?

And the Ford rally cars that used to have solid axles used the system I mentioned above, contrary to what you may think. I built enough of the things!!

Then again, you still believe in 'roll centres' Not all that that's put in print is current, nor backed up by scientific fact.

[Edited on 16/10/05 by Syd Bridge]


Dale - 16/10/05 at 04:45 PM

I see a thousand watts links bolted to the diff every day- crown vic police crusiers- but I believe it is done that way as its probably a couple of seconds faster to put in and does not require a center section in the frame to bolt the section to.

You would be suprised as to how well the big car handles its 4 link live axle same as the locost with a coil over spring type of rear -or air bag. and unequal length A arms on the front.

Dale


Bob C - 17/10/05 at 09:10 AM

So - has anyone driven a powerful car with this kind of "torque tube" wheel torque reaction control? By my reckoning the wheel torque reaction will try to compress the springs leading to extra "squat". Does the extra squat lead to extra wheelspin?
cheers
Bob


britishtrident - 17/10/05 at 01:05 PM

Rover used a torque tube on the Sd1 including the racers, Opel at one time used right across the range including the Comodore racers.

I think also the Chevette HSR 2300 might have used a torque tube but can't be sure.


britishtrident - 17/10/05 at 01:11 PM

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britishtrident - 17/10/05 at 01:15 PM

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