# attn custom car builders what do you think?

**URL:** <https://forums.speedlife.net/t/attn-custom-car-builders-what-do-you-think/247839>\
**Category:** Shift518 Automotive\
**Created:** [October 25, 2009, 2:55pm UTC](https://forums.speedlife.net/t/attn-custom-car-builders-what-do-you-think/247839 "2009-10-25T14:55:55Z")\
**Posts on this page:** 1\
**Showing post:** 9

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**Author:** ![skiboard06](https://avatars.discourse-cdn.com/v4/letter/s/898d66/32.png) [@skiboard06](https://forums.speedlife.net/u/skiboard06)\
**Post date:** [October 29, 2009, 9:41pm UTC](https://forums.speedlife.net/t/attn-custom-car-builders-what-do-you-think/247839/9 "2009-10-29T21:41:31Z")

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> [@smokers...](https://forums.speedlife.net/t/smokers/24893/17):
>
> First, you’re working backwards. You need to decide what type of suspension the car will have then build a frame to suit. every suspension setup has it’s own geometry, mounting points, and opoosing forces and the chassis must be suited to them. If you’re going to be designing and building your own components you need a proper suspension program, even something like Suspro3d is better than nothing. Datums, CG’s, roll centers, instant centers, etc all need to be calculated otherwise you could end up with a wildly dangerous car.
> 
> Once that is ascertained, you can then work the chassis into the car. In that sense I suggest picking up some chassis theory books online and do some reading. You appear to be starting with an exiting unibody chassis, which will help you keep the overal tube setup rather simple and still maintain some decent rigidity in the overal chassis.
> 
> Also jig the chassis before you cut anything, as unibodies with welded in cages can be under some stress and if you relieve the unibody in a stressed area you can induce a frame twist. One that may be extremyl difficult if not impossible to eliminate without a frame pull machine.
> 
> It’s ALOT of math and work, and often for these projects it’s best to work with components that have already been proven and are readily available. There are a few companies out there that produce some rather neat and effective front/rear suspension cradle assemblies that can be modified to suit just about any application. They’re also mostly catered to big V8 setups. Fatman Fabrication is one such company that comes to mind. Also, using front Corvette C5 components and cradles is a SOLID way to go. One such company that does just this is Factory Five, and they use those exact components in they wild GTM supercar.
> 
> I’ve got about 4 years into designing my monocoque chassis/suspension setup in Solidworks for my kit car that I’ll be starting this spring. Hundreds of changes and revisions before any metal has even been cut. Take your time, definitely use the right setup tools, and you’ll have a solid setup. IF you have specific questions, shoot me an email @ [r247motorsports@gmail.com](mailto:r247motorsports@gmail.com)

Without some of the details this was going to be my exact post.

You are undertaking a very in depth project;

I can’t tell from the pictures whether you plan to use the unibody or ditch it for an entirely tube frame setup with the VW shell on top?

Jeff made a great point earlier about building for a particular series or race class, if you don’t do this you can end up with a car that is worth close to nothing after you have spent A LOT of money/time on it. With how extensive the cage looks, you are headed for some very high dollar classes (i.e. multiple $20k sequential transmissions, $10k dampers).

The thousands of engineers that designed VW’s original suspension geometry had to make a lot of compromises, but still ended up with an intelligent and usable setup. To better what they did with take some serious calculation and testing with suspension geometry changes.

I would seriously recommend you try to hire boxersix for consulting work as you design the chassis, he is competent and educated. It’s also great to have a second set of eyes look over plans before any expensive fab work is done.

edit: I forgot to say that I am juiced to see how this progresses, has the potential to be awesome.

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