bmw e30 318i donor

Originally Posted by rmccomiskie

Thanks for volunteering Chris. Of the 2 drawings you previously posted, one shows the fabricated part straddling the upper mounting ear and the other shows it bolted to the side of the ear. Even though it might mean the fabricated upper ball joint attachment has to be angled somewhat for proper geometry, it seems to me that the straddled approach would be less likely to flex the mounting bolt.

In your design, perhaps you can consider instructions that accomodate different KPI, caster, scrub radius, wheel offset, tire size. Something like a simple geometric drawing that shows where the upper ball joint has to be given all the parameters. Just my 2 cents.

Waits eagerly...

The two versions of the fabrication exist because I haven't done any work on the geometry.

I'd better explain that, One of the set ups will be better for caster, but I don't know which. Obviously the version with the upright stradling the strut mount would be prefered (double shear) but it might be that the geometry requires the offset version, for example if the balljoint articulation is beyond limits.

As I said in my previous post it's an oportunity to decide your own parameters, suspension design is facinating but always a compromise with opposing factors and I think it would be beyond the scope of a build your own type book to do justice to the subject. I'd recommend "competition Car Suspension" by Allan Staniforth (RIP) if you want to get into it.

The design would be my best compromise taking into account weight, wheel rates, required roll centres, etc with adjustability built in for people to tinker.

Camber adjustment is easy to accomodate if the design uses the Transit drag link end, caster can be adjusted by spacing the bottom and top wishbones (not a lot I'll grant you) KPI is really a function of design, and needs to be set when the upright is made, although camber changes will alter the angle slightly, and scub radius can only be altered, when KPI has been set, by varing wheel offset.

It's worth noting that lowering the top wishbones will extend the roll centres almost to infinity, efectively making the set up into a swing axle - think VW Beetle - it'll keep the chassis off the floor but it was abandoned for performance cars in the 1930's!

Cheers

Chris