Jtoby - Camber Curves

[Bino]

So, I'm a relatively new DSM owner, but I'm not new to the art of performance driving or performance cars. I purchased my GSX with the goal of a daily driver and competitive road-course car on the weekends and some autocrossing to fill in the voids. I've done a lot of research and it's pretty clear that the camber gains from our suspension are pretty 'nil. I was wondering if anybody has considered lowering the upper A-arm mounting point (on the chassis). If this point could be dropped, perhaps up to an inch, it would dramatically increase the camber curves of the suspension, and probably increase cornering prowess dramatically. It seems like there are no problems making new A-arms to try and improve camber, a new a-arm would likely(surely) be necessary if the mounting point were dropped.

Now, I am rather interested in pursuing this further, I figured I would find out if anybody has accurate data for the suspension pickup points? I'm going to crunch some numbers WRT camber curves and suspension geometry. See if I can find some kind of happy medium (every suspension tuning/designing experience is full of compromises) that could yield some form of decent camber gain.

I realize that our cars are unibodies and creating new suspension pickup points isn't just a walk in the park, but it's no more in-depth that the AWD Spyder conversions, etc. It seems plausible that a few dedicated weekends on jack-stands with some calculations and some sheetmetal(reinforcement) and a welder could possibly yield some good results. If anybody has any other theories or ideas relative to these thoughts, I'd love to hear them.

 

[aves911]

You wouldn't necessarily have to do any welding or make new arms. There is plenty of thread on the a-arm anchor bolts. I have toyed with the idea of shimming the upper a-arm pivots down a little with washers to pick up some camber and change the curve. But I have yet to decide which suspension modeling software I want to buy and don't want to do anything blind.

Its really not a bad idea, problem is that most guys here who would do it compete and I would image that this type of modification isnt allowed in the classes they want to stay in.

-Jacob

 

[jtmcinder]

Actually, 2G front bump-camber curves are relatively constant at around 3/4 degree per inch, which is pretty darned good for a production car. How is this possible? At first you gain camber from two sources: the lower lateral arm coming up to being level (and, therefore, pushing out at the bottom) and the upper arm swinging up and in (and pulling in at the top). After the lateral arm becomes level you start to lose some camber from the lower end pulling back in as bump continues, but the upper arm is now swinging in so fast that this is more than made up for. Thus, you end up with a nice straightish "curve."

Note that this is the huge advantage of double-wishbone over struts: that you can continue to gain camber in bump through-out the travel. The curves for struts are flatten to begin with and are often not straight. But strut-type suspensions weigh less. No free lunch and all that rot.

Yes, if you effectively shortened the upper arms (which is exactly what eccentric bushings for the upper-arm pivots do), you start with more camber and gain it a bit faster in bump. But you are never going to be able to cancel the loss in camber due to body roll without radical reworking, so you need to start with 2 degrees or more to get these cars to turn well.

- Jtoby

 

[jtmcinder]

More

If you really want to steepen the curve, start with those bent and adjustable pivots like the ones designed to *delete* negative camber on lowered cars. Then drill new holes in the A-arms to make them shorter. (You will have to also remove some of the cross-metal on the top of the arm, but that shouldn't be hard.) This would allow you to have less static negative camber (for launching) but a very steep curve (for cornering). It's a legal mod in SM because the new pivots are allowed under ST's camber-kit rule and you can do anything you wish to the moving parts in SM.

Been on my to-do list for a while, in fact. I didn't mention it before because of some stupid notion of maintaining my competitive advantage. Like no-one else could think of this. And like a 2G has a chance against M3s, EVOs, and STis.

- Jtoby

 

[Bino]

Thanks for the replies, very useful and insightful. I'll hopefully be tackling some of this in the next few months and will definitely let you know what I find out.