reversing trailing arm suspension?

[johnd]

can this be done?

this is a conventional imp set up


this is what i plan to do


if i cant reverse the rear suspension set up i will need to make some sort of subframe/custom set up...

I'm just really wondering, its called a trailing arm because its meant to trail? how would running it in reverse effect handling and the safety aspect?

[gurnersimps1963]

Hi John,not sure about the trailing arm question mate but there is an Imp with similar configeration on Imp club site...
forum.theimpclub.co.uk/viewtopic.php?t=5981

[johnd]

cheers mate, the more i think about a reverse trailing arm it seems unsafe

[composimmonite]

What would you attach the suspension to ? There is very little strength in rear panel (which is bolt on anyway) area so that would involve building a subframe that could carry the loads back into the main shell. Also when you consider the cutting about of the shell will then require a BIVA you might as well go the full spaceframe route. That way you could use what ever suspension you liked both front and rear.

Paul H

[RobinJI]

There's no reason it wouldn't work, and it has been done, and worked perfectly fine, 2cv's use it on the front for example.

However, a quick google tells me the Imp actually uses semi-trailing arms, not trailing arms. These have an angled pivot, which causes an increase in camber and toe in as the suspension compresses. If you were to turn it around, you'd still get an increase in camber, but the suspension would toe out as it compressed. This could make for really quite unstable handling, so I wouldn't advise it. Besides the geometry, you'd also be adding a fair bit of weight out back with the beam the arms bolt to, and even more by the time you reinforced things enough to fit it there.

I'd actually expect the XE to sit rearward enough to fit in front of the mounting beam for the rear suspension arms, so you could make some new L-shaped arms that allowed clearance for the engine but fitted in the standard mountings.

[stealthstylz]

If you're planning on more power than standard/going fast then no, will have less traction.

Matt

[stealthstylz]

Also looking at your pic you could probably get double wishbones in there fairly easily.

[johnd]

what do you mean double wish bones? I'm entering this blind

[DWDarkWheels]

What you're describing is 'leading arms', and was used in Formula 27 cars, one of the many Locost Lotus 7 clones.
As you can see it needs a serious structure at the rear to support it.



If it's well supported, I can see it working. You can also see how there are various mounts for the arms, making it adjustable. Depending on the angle of the arms, it might prevent the rear squatting under hard acceleration.

Here's another idea if you're struggling for space : one trailing, one leading arm

[RobinJI]

^ Those examples are leading radius arms on a live axle set-up, rather than true independent leading arms. 2cv's use leading arms on the front:




As I said, using the standard Imp beam the wrong way around would give some strange geometry changes through the travel.

I'd be tempted to see if there's any possibility of fitting the engine in around the existing beam with modified suspension arms before looking at completely changing things. The XE will be a lot narrower at the bottom than your drawing makes out.

Something like this if possible:



If that's not possible, then you could look at making longer trailing arms and moving the beam forwards a bit for some more clearance, or failing that making a MacPhearson's strut set-up (like the front of most FWD cars use).

If you're still not sure what double wishbones are then google it I'd have said you'd probably struggle to get a worthwhile set-up in the back of an Imp around the XE. You'd end up with very short wishbones to fit it all in there, which aren't ideal, and the frame to carry them would be quite messy. Possible, but you'd need to put some thought into the design of everything to make it worth while compared to the simpler options.

[robg2]

Reversing a trailing arm or semi-trailing arm setup doesn't sound like a good idea to me. In addition to Robin's observation about toe-out vs suspension travel, you'll also end up with pitch issues as the suspension will be diving instead of squatting. Together with more power and more weight at the back, it could really be ill-handling.

If I was doing this, I'd go down the local scrappie and relieve an Impreza of its rear end. They use a fairly simple strut layout meaning that sandwiching an XE power unit in should only be a case of appropriate driveshafts / mounts / gear linkage.

Darryl - your photo is a 4 link setup on a live axle, which isn't the same as leading arms.

[robg2]

Feb 4, 2012 12:37:25 GMT gurnersimps1963 said:

Hi John,not sure about the trailing arm question mate but there is an Imp with similar configeration on Imp club site...

No there isn't!

This is the one you're referring to:



That's basically a K series Metro engine & box & front subframe in the back of an Imp. You can see the steering rack...

He's modified it to run coilovers rather than the original Hydragas - not only sensible, but the only practical way to tune the setup (ie select appropriate spring rates).

In my opinion, that's a sensible way to go. It means you only have to fabricate a means of locating a subframe and gearlinkage* in the back of your Imp rather than having to make your own driveshafts / wishbones / hubs. Making your own bits carries a high risk of having something break when you're driving, and you really don't want that...

*Instead of a Metro front frame, you could use an MGF rear frame. Then the gear linkage already points in the right direction and you don't have the problem of having to lock the steering rack.
If you used a MG TF frame, that already comes with coilovers.

K series in MG ZR form comes with 160bhp, which is more than a standard XE. There's a factory K series turbo too (Rover 75) which could be a good way for tuning.
In any case, 160bhp will be more than enough in an Imp.