Originally Posted by
SleeperBug
Basicaly I want to lower a old vw beetle body onto a new rolling chassis with matching body mounting points.
This has been done so often to Beetle's over the course of its long life that I'd think you'd be able to get a good basic structure from VW owners clubs etc.
I know that things like the pitch of the lower a arm can effect dive / anti-dive. I just don't understand the relationship between cause and effect that well on suspension design.
Do you want to ?
Your optoins are to take a working suspension and build chassis muntin points to take it - so getting all the benefits the original car had.
Or develop your own suspension - making it better tuned to your needs.
BUT, you will have to consider how your local vehicle licensing laws work. In the UK, if you build it all yourself, you MUST get a written engineers report that it's sound and that can be expensive for 1-off. Using donor parts reduces that effort and cost.
If you DO want to develop it yourself then it needs a LOT of study. There are many good books out there on racing car design which covers all aspects. There is VERY little on road car design - so you may not design something easy to park for example ( caster angles ) !!
As well as study, it usually involves trial and error. I know guys who've built their own grass-trackers and autotest cars and they usually went through 2 or 3 iterations of suspension and chassis before they got soemthing 'right' 
I would like to use production suspension parts, a-arms, spnidles, etc. Maybe just modify the upper mounting points of the struts. I was thinking of trying to use an MR2 or some other already in production cheap mid engine car. This way it's roughly set-up for the mid engine weight etc...
Good choice - so you were probably already aware of the pitfalls above 
Some still exist as taking an original suspension and chanigng it's height and distance-to-centre mountings can alter the characteristics.
Why dismiss torsion bar ? ( Especially if you have contacts for steel and machining ) It was good enough for the 911 ( and my Matra's )
The fundamental drawbacks of torsion bar come if you want large amounts of movement. In a 'dropped' car that's not an issue. The it's down to being able to source steel with the torsional compliance required. That's a specification task and maching job to determine the right lengths. The BIG advantage torsion bar brought was compactness.
However, with modern low-cost VERY good coil-overs, I'd go thate route too
To the design and fabrication.
There are 2 approaches ....
What I've heard called the "hill-billy" approach which is to slap some steel on in roughly the right place, weld it up and if that doesn't work, weld another bit of steel on until you get get it working ( Jesse James of bike building fame ). So don't do too much design and build it-situ to match the bits you've got.
Secondly, with the advent of cheap 3d software you can model the whole thing on a PC. A guy near me does kits for Vipers and it is an excellent piece of enginnering and construction. He did the WHOLE thing on the PC before he made a single cut, weld or lay-up. To do this you want to get all the measurements for the suspension you intend to use ( this can either be done by measurement or from manufacturers bodyshop repair documentation ). Then you can design a chassis to those measurements, see how it fits together, check clearances etc. The Viper guy reckoned it took him 3 months to get his done, but that included body parts.
If you want a car to use on the road with others then safety of you AND OTHER ROAD-USERS becomes VERY important. Do you have the confidence to be able to do the structural design of a chassis to withstand the road shock and not crack ot shear ? What about impact ?? For these reasons I'd suggest contacting a VW club and ask opinion and seek professionaly designed chassis. ( Again with a little expenditure in software it's possible to do stress analysis on a chassis to 'test' for strength. Kind of doing the "hill-billy" stuff but on computer If you're only going to do track and closed roads stuff then some of this is less important - one of the grass-track designs I've seen the guy says he has to replace one of the cross-members on the chassis "regularly" because it bends !! That's OK if it's only YOU at risk, unacceptable if there are others.
Wow, feel like I've written a lot and only told you the difficulties and problems and how hard it is. Counter that with there is NOTHING as satisfying as getting something you deisnged and built onto the road/track.
You've lots of study ahead of you to make this work but hopefully can contact some local guys who can help. BTW, some of the 'best' fabricators are hot-rodders, so look up some of those clubs too.
Good luck and ask any question you like, You'll find folks here on UCP who've some experience in almost anything and willing to help.
EDIT: For the ultimate VW 'sleeper' do a google on "uniroyal team challenge". This is a Beetle look-alike spaceframe chassis race car here in Europe. You could get some ideas from them on the design [ It's not a complete Beetle shell though, it's just made to look like one ]
Last edited by Matra et Alpine; 07-28-2004 at 03:18 AM.
"A woman without curves is like a road without bends, you might get to your destination quicker but the ride is boring as hell'
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