Lightweight (but strong) rear suspension ideas????

[stealthstylz]

After talking to various people who race/rally Unos, apparantly the biggest limit to how good the handling is is the rear axle/suspension setup.

As standard its a H beam, mounted with large bushes (3" diameter ish) at one end. The springs are mounted partway along the axle, with the shock absorbers mounted right at the very ends.

The design and build of it manages to make it both really heavy and not very strong. The main part is made of a piece of angle iron. People have boxed this in using an extra plate to form a triangle section, but this adds even more weight.

I'm trying to come up with ideas to replace the rear suspension. I'm thinking of making some trailing arms, similar to whats on a BMW (but without the driveshaft bits).

Would this sort of setup cause any handling peculiarities on a FWD car?

Some trailing arm pics





Matt

[rysz]

Minis use trailing arms do they not? Coupled with some decent coilovers to get the springing and the damping, I would imagine you would be fine.

Rysz.

[paulw]

I think the reason why it's a piece of angle is that it's not meant to be very strong, in a way. That angle piece is designed to twist and act like an anti-roll bar. boxing it will stiffen it, but it doesn't allow for much adjustability if you find it wants to dive off the road backwards...

Semi-trailing arms give you changes to the toe-in/out as they go up and down - this works ok on rear-wheel drive cars as they will tend to to toe-in to counteract power-on oversteer, but I think you would end up with a real handful if you put them on the back of an Uno.

I think you'd be better staying close to what you have, and either strengthening existing bits and improving the bushing etc, or refabricating parts in tube if possible to closely replicate the original geometry, to be honest.

[stealthstylz]

Surely if I keep the pivot points perpendicular to the car the toe in won't change at all? The wheel will move forwards and backwards in the arch with suspension travel but the arms would be quite long so it shouldn't be too bad.

Matt

[kee]

how much work are you willin to put in?

you could try find a car with similar track width on the rear, but has independant suspension.
i hear good things about ford focus rear ends however the track is probably bigger, have a look around.
beam suspension is cack the only real solution is independant of some sort

[kee]

of course the alternative is spaceframe/tube framing the rear and double wishbones

[stealthstylz]

Double wishbones would require far too much extra chassis and therefore extra weight, for not a great deal of gain. The good thing about trailing arms is that it will barely need any extra chassis, just some mounts welding onto the bodywork. Gonna get the car stripped and see what I can come up with.

Matt

[popuptoaster]

Fiesta rear end might do the job, but if your going to all the effort of changing the rear end i'd look at some fwd race car rear ends and duplicate that, might as well do it right if your gonna do it.

[Rich606]

I don't think it should cause any handling problems - Team Dynamics/Halfords had to do basically exactly the same thing with the BTCC Honda Civics. They replaced the rear suspension with trailing arms. As you have to keep the same suspension pick-up points these arms only attached at one point, which would allow a lot of sideways movement. So they designed the arms so that they met up under the centre of the car, at a large bearing so that the two could move independantly.

There was an article on it in Racecar Engineering magazine back in March, unfortunately there's nothing on their website, but PM me an address and I could send you a photocopy on Monday if you want a better explanation.

[sammm]

What about a single traverse leaf spring using a composite spring to keep the weight down?







Or couldn't you just replicate the standard arrangement in a heavily triangulated/spaceframe fashion to reduce weight and increase strength.

[paulw]

Dec 5, 2008 15:24:44 GMT stealthstylz said:

Surely if I keep the pivot points perpendicular to the car the toe in won't change at all? The wheel will move forwards and backwards in the arch with suspension travel but the arms would be quite long so it shouldn't be too bad.

Matt

Sorry, I hadn't realised you meant pure trailing arms - the semi bit means the pivots are angled (like on a beemer). With trailing arms you don't get any toe change or camber gain in roll, same as the standard set up.

You'd have to find a way of giving yourself the roll stiffness that you'd lose from the beam, but you could do this with an anti roll bar. Even if you built fully independent suspension you'd end up linking the two sides with an anti-roll bar, the standard system is just a simple, non-adjustable way of doing that.

But maybe you can modify what you've got - Have you got any pics of the standard set up? Any idea which bits are the weak spots?

[RA40tony]

Aren't the cinquecento and seicento fitted with independent rear suspension? Seem to have a hazy recolection of mine not having a rear beam.

[stealthstylz]

I'll get a photo of the standard beam. I could make a new solid axle from tube, but it seems silly to go to all that work and not switch to an independent system.

Matt

[Colonelk]

cavalaier GSi and calibras had IRS on FWD models (semi trailing arms) so theres nothing inherent in the design that should cause an issue. Those two are pretty rubbish examples though as the suspension weighed a fair chunk more than the beam IIRC!

[gn3dr]

Have a look here for some ideas
www.hh-ms.com/HHMS_rear_independent_sus.htm

[Adam]

£4k

Bloody hell!

[stealthstylz]

Haha thats exactly the same idea as I was planning to do.

Matt