Fabricated Suspension Arms

[Duk]

I'm looking at fabricating some front suspension arms (unequal length A arm/wishbones) for 1 of my projects and was wondering if anybody knows of any legal issues that would result?

2 things that I really want to achieve with the fabricated suspension arms are an increase in track width, without changing the scrub radius. So wheel spacers are out.
And a significant increase in castor angle by moving the lower balljoint forward as I currently have clearance issues and still want more castor.

BTW, it's a road car.

[Sam_Q]

well before even going into the legal issues of the arms themself there are legalities involving the track width itself of a vehicle. So it sounds like your already stepping on the wrong side of the law.

[brett_celicacoupe]

you would need to prove structural equivalency in some way for a number of loading modes.

this may mean destructive testing for your prototype and the OEM item.


this would all need to be done in consultation with an engineer that is happy to sign it off

[Lachie]

How much castor are you currently running on the car? If you increase the mechanical/caster trail too much, it will swamp out the feel of the pneumatic trail and you can't feel when the tyres are about to let go. Believe me, it makes for a very interesting car to try and drive on the limit

[RobertoX]

Basically call an engineer and see what they would require to sign off on it first...

It'll probably end up what Brett Celicacoupe is saying but they may also have an issue with increased castor. Even if the arm is equivalent in strength to the original, the change in castor will change the way the arm takes the load so there will be a different strength requirement of the arm itself...

Also what Lachie says is true, I reckon he learnt from the same place that I did (FSAE) that adjusting castor to unreasonably high levels leads to a car with poor feeling and heavy steering. Ask the engineer if its possible to make the arm adjustable at all.

you would need to prove structural equivalency in some way for a number of loading modes.

this may mean destructive testing for your prototype and the OEM item.


this would all need to be done in consultation with an engineer that is happy to sign it off

[Duk]

Cheers for the input guys.
After giving it some more thought, it's being put in the 'to hard' basket.
I'd still love to do it, but maybe for a track car to avoid the legal issues.
BTW, castor angles aren't huge, I'm around the 5.5-6* but the wheel could probably do with some more clearance at full lock and bump. I was after 6.5-7* to help maintain negative camber with body roll.
It's a relatively narrow car with a fairly high rate of roll, hence my reason for an increase in track width and castor.
Yes I know most people would say "Just use bigger antiroll bars." but I'm trying to maintain as much compliance (already have higher rate front springs, but want higher again) as I can while controlling weight transfer and have better control of the camber angle when the weight does transfer during a turn (couln't really do much about the dive under brakes apart from the increased spring rates ).