Swing Axle suspension

[choc-ice]

First post here, hopefully I can get some help from you guys who understand suspension geometry better than me, and better than just reading from brochures! Hope it's in the right forum?

I've got a 1961 VW Beetle, double trailing arm front suspension and swing axle rear suspension. I've lowered the car by 2 inches so the rear end now gives about 2º negative camber when static, front is lowered to make the car level.

The car is just a weekend toy for the road but I'm wondering how to improve the car's handling. It's got an 80bhp engine (twice standard power!) and Porsche 356 finned drum brakes so it goes ok for a 45 year old slow car.

There are various schools of thought for swing axle suspensions so can anyone throw some light on what would work, and why? I know of:

1. Replace it with semi trailing arms from a later Bug. Lots of work to the chassis, needs a different gearbox to accommodate different driveshafts. I really don't want to do this.

2. Camber compensator. Does this really transfer load from the outer wheel to the inner one during cornering?

3. Larger front anti roll bar. This seems like a bit of a sneaky work-around, let's make the front end wash out so early that you never get to the feeble grip limit on the rear.

4. Diagonal links. I had an old Renault 8 that had these on the rear swing axles and it seemed to handle well, it could be drifted around roundabouts like a very slow Fast & Furious car. How and why does it work, or was the car just better balanced than the Bug? The VW has a trailing arm attached to the torsion bars so I believe the suspension geometry is different to a pure swing axle. Does the Renault diagonal link effectively make a 'longer' trailing arm?

5. Limit straps. I had this on an old rear engined Tatra which wasn't exactly a model of high speed stability. Wouldn't this lurch a bit when they came into play? Anything sudden while the rear suspension is on its way to positive camber can only be a bad thing I feel!

Thanks for any help, feel free to talk about things invented after 1930 after I've gone

[knighty]

swing axle suspension in a full bodied beetle is bad news to be honest.........I have a UVA Fugitive-4 on beetle swingaxle rear suspension........its OK as its so light there is hardly any body roll........formula Vee's are the same - but they run some nice anti-roll bars too.......if I was in your shoes I would be looking at limiting the body roll as much as possible - so thats front and rear anti-roll bars.........as the beetle centre of gravity is so high - when the body rolls too much - you get buckets of positive camber on the outside loaded wheel - the outside wheel tucks under .........and you can roll the car

[choc-ice]

I always thought that a rear anti-roll bar was a bad idea as it'll promote oversteer.

But maybe the fact that it's limiting wheel travel and body roll is worth more than the increased rear roll stiffness?

[phoenix]

I believe that the Formula V people use a 'Z-Bar' anti roll bar as the best solution. Don't know if such an arrangement can be made to fit in a saloon layout though.

[choc-ice]

Yes, the z bar originally came from the VW saloon cars, but it was only fitted with softer torsion bars, I think it's the softer torsion bars that actually improve rear end grip?

Is there anywhere that has tuning tips for Formula Vee cars, or do competitors like to keep their ideas secret?

[Al Weyman]

There is is a section on these in Fred Phuhns 'How to make your car handle' including the Z bar with pictures and diagrams, may be worth getting hold of a copy.

[choc-ice]

It's years since I looked in there, I'll see if I can dig that book out again!

Thanks

[kramer]

You could combine a camber compensator (transverse leaf spring) with a limit cable to prevent positive camber. Lots of Vees use that pretty effectively. However, you lose a lot of droop, so if you're looking at off-road use, this won't help.

The VW 1500 Auto had the good rear end - the double trailing arm type, as did the later Type 3s and Superbugs. Maybe it would be simpler to go to a different chassis?


Kramer

[choc-ice]

The more I think about it, the more the limit straps seem to be the answer. I don't want anything to make the rear spring rate harder as that's bound to lead to more oversteer, all I really want to do is stop it going into positive camber.

Later cars with semi trailing arms are better, but it would mean a huge amount of work to weld on brackets (there's not much space with the bodyshell in place) and it would need a new gearbox for the different driveshafts. I've currently got a high ratio box from a 1500 Bug so I'd have to go shopping for a 1302S or 1303S box for the conversion.

The other problem is it makes the rear track wider so my 6" wide wheels wouldn't fit under the standard arches.

[ubrben]

The Beetle was never designed to be a good handling car - mearly acceptable. It's a mass production car designed for economies of scale not performance.

Ben

[JohnD]

choc-ice,
Do you know that the car that shares your swing axle design ( concept, not parts) is the Triumph Spitfire?

That was greatly improved by a late modifiaction to a 'swing spring'. This uses a different type of transverse spring, that is allowed to pivot on a box over the differential, so that the body can roll, without forcing the wheels to change camber. It is a very effective device.
No idea if this has ever been 'transplanted' to a VW. Anyone know?

John

[kramer]

Sorry - I forgot something. You're exactly right, choc-ice, about the camber compensator making the rear end too stiff. Vees, if they have this, don't have the rear torsion bars any more. They will often use a coil-over shock to get the spring rate right. The compensator also acts as a sway bar, or you can use the previously-mentioned z-bar as a spring too.



Kramer

[terence]

Originally Posted by JohnD

choc-ice,
Do you know that the car that shares your swing axle design ( concept, not parts) is the Triumph Spitfire?

That was greatly improved by a late modifiaction to a 'swing spring'. This uses a different type of transverse spring, that is allowed to pivot on a box over the differential, so that the body can roll, without forcing the wheels to change camber. It is a very effective device.
No idea if this has ever been 'transplanted' to a VW. Anyone know?

John

You cant use the Spitfire one,but they can be obtained from VW tuning shops

[JohnD]

Terry,
I'd be most interested to see how VW tuners do that, and compare with the stock Triumph one. Any links to suppliers of VW swing springs, please?

John

[choc-ice]

Originally Posted by ubrben

The Beetle was never designed to be a good handling car - mearly acceptable. It's a mass production car designed for economies of scale not performance.

Last edited by dtype38 : 10 Nov 2006 at 16:26. Reason: - uncalled for sarcasm -

Ben

Don't worry about editing out sarcasm, I'm well aware of the handling limitations of the Bug. I've driven lots of cars over the years, some were great handling: Alfasud Sprint; Suzuki Cappuccino; Peugeot 106 Rallye, and some were dire: VW412; Capri 1.6 amongs others!

While I know it's not possible to turn a 45 year old cheap car into an Evo eater, I'm interested in making it better and trying to work out how. It's from a healthy disregard for 'catalogue tuning' as much as anything else!

When I did chassis engineering at uni all those years ago, the emphasis was obviously on more modern suspension systems, but as was proved with the Renault 8 Gordini and Alpine A110, reasonable handling is possible with swing axles.

The camber compensator to fit VWs looks like this


I believe they're bolted to the gearbox, but wouldn't it be more effective if it could pivot, as said above?

cheers for the words of wisdom guys!

[Al Weyman]

Funny, years ago I had a bog standard 1300cc Capri with the lighter Kent engine and I thought it handled really well, much better than the 2 litre Pinto I had later.