is anyone running a trailing arms setup?

[my2000apb]

similar to old rally cars? is there a need to a road course vehicle?

ive got my shell down to nothing and want to make them now vs later if its something that should be done


for the vrt cq in my sig

[Error404]

I'd have thought it was to add some bracing to the wishbones for reliability over a rally stage, I cant see a tangible benefit for a road car TBH

[my2000apb]

yeah I agree, my real question wa more if there is a benefit?

did the rally cars use it to keep big hits from messing up alignment? or is there enough flex that its still beneficial on a road course car?

[Error404]

I'd say it was used to keep them from breaking the wishbones / subframe over big hits on rough stages, rather than to maintain geometry. AFAIK they used rubber wishbone bushes anyway so my guess would be that longevity and compliance came before geo in the scheme of things
Benefit on the road? I'd doubt you'd notice, but always good to experiment. You could weld in the pick-up points then you can always test them out and see if they do make a difference?

[quattro84]

These do not aid suspension geometry whatsoever, the standard setup is stiff enough. You need insane levels of acceleration to make them work. When they do work you need a new bodyshell because it rips it out of shape beyond repair (replacing is cheaper)

If you work the geometry out dynamically you will find out that it won't work since the angular component of the trailing arm swinging asks for elongation or movement of parts.
Totally agree with Error404 (again ) the only benefit would be to finish the rally stage with four wheels centered in the arch, no matter what state. Helps bodywork metal fatique (over time) around critical areas such as subframe & wisbone mountings and bolts shearing.

Added some pics of factory used braces which fit the typ85 chassis.

[Error404]

Great pics, thanks for sharing
Is that a urq shown in the shots?

[quattro84]

No, something special, sportquattro sedan based on the 80q

[Error404]

Thanks, not seen that before. Do have have any more information on it or a link to a build thread etc?

[quattro84]

Not really, it's something i found strolling around on facebook (haha you'll be falling from your chair now )

[my2000apb]

You need insane levels of acceleration to make them work. When they do work you need a new bodyshell because it rips it out of shape beyond repair (replacing is cheaper)

.

can you please explain that a bit more

[quattro84]

It's all about degrees of freedom. Different joints allow different degrees of freedom, like a ball joint allows rotational movement around it's axis next to bending in all directions, while a bush end can only pivot, etc.

Under free acceleration the forces in the trailing arms would be very very low since the S2 McPherson suspension setup is stiff enough to resist movement in longitudinal direction (assuming solid mounts/uniballs/stiff rubbers/zero play)

So, when pulling forces are working on the trailings arms it would mean that the entire suspension sub assembly is moving away from it's original position which means that at least your track/steering rod and wishbone are bending for a considerable distance.

When does it happen? If you hit a side kerb at full chat for instance. Wheels stops but car inertia will push it along.
The trailing arm will save your sub assembly from shearing off the body but it'll deform it anyway.
The forces acting on the rod need a reactional force to compensate it, and that force will warp your underbody or whatever it's connected to.
That's why most bodyshells in rallysport don't age very well. Cages are great but make it impossible to straighten a shell, tubes itself do not make them bulletproof neither since the body will flex anyway and give way at some point.

[my2000apb]

ok hmm, good info
but it seems like you are referring it a trailing arm that would be in compression/tension rather than being properly designed to work as a third door hinge

good pics at bottom of page
http://www.motorgeek.com/viewtopic.php?f=6&t=12422&start=225

[my2000apb]

updated with some pics