[Tambohamilton]

Originally Posted by fe1rx

The OptimimumG approach is looking at steady state handling balance.

Good point.

Originally Posted by fe1rx

I think it is fair to say that track cars should not be on their bump stops under steady state maximum cornering conditions, except when they encounter a bump.

Yes, agreed. As stock, it only takes a few mm (if any) bump travel to engage the "auxiliary springs", though... Something I'll change a little with all of this, but currently that's how it is for me.

Originally Posted by fe1rx

Generally though, bushing windup acts like a spring in parallel with the main spring, so the wheel rates from each source simply add together. The same is true of a bump stop, when it is engaged.

Thanks. That's what I needed to know! I just couldn't settle on how the interaction would go numerically, in my head, and nobody at google seemed to have an answer either

Originally Posted by fe1rx

Bushing windup of the ARB bushings should be negligible. The ARB should rotate in the bushings, not bind to them.

I have an OE E93 M3 rear ARB on my car right now...the bushings for it are the same as the E90/92 M3 items, which fit a 20mm (vs 23mm?) bar. The bushings definitely clamp down hard onto the E93 bar, and I'm fairly sure would add significantly to the rate. Next time I have it apart, I really should drill out the mounts a little, to ease the pressure.

Originally Posted by fe1rx

Another confounding factor is that bushing rates can be expected to be both temperature and rate dependant (I expect stiffer at higher rates and softer at higher temperatures). This is certainly true of bump stops.

Yup...I won't even be thinking about that - beyond the scope of my project, and my driving


Thanks for the input!