Black & Tan 332iT

[Bry5on]

If I understand you correctly, you are saying previously you thought the hub pivoted off of the inner control arm joints and the trailing arms just set toe. But in actuality the hub pivots off the front trailing arm location and the control arms just set camber?

Not exactly, but something close to that yes. Previously I assumed that the rear control arms inboard termination point was close to the axis of the hubs. If that were true, you could calculate the instant center and roll center pretty accurately without factoring in the location of the trailing arm bushing.

The e46 hub is always pivoting around an axis that includes the trailing arm bushing on that axis. The second point that defines that axis is a virtual location where the upper and lower control arms meet (I’ll get to this in a second). If you extend that axis in three dimensions, the instant center is the point where that axis crosses an imaginary vertical plane that intersects both rear wheel/hub centers. Then the roll center is the intersection point of the left and right instant centers.

Ok, so that virtual point where the control arms meet (above). It’s always moving with suspension travel, it’s not technically fixed in space like a true semi trailing arm. However! Because the two inner mounting locations are SO close together, that point baaarely moves as we sweep through suspension travel, which effectively approximates a static point, like a semi trailing arm.

So in conclusion, the e46 is not technically the same as a semi-trailing arm rear suspension, but practically speaking it behaves the same with a very small deviation. That amount of small deviation is related to providing the degrees of freedom necessary to easily adjust camber and toe without changing the suspension geometry much at all.

So, for all intents and purposes, a semi-trailing arm suspension that has adjustable camber and toe. Hopefully that was followable.

[Bry5on]

What would it take to get / make a Mullet tune for those of us w/ CSL airbox + CSL software and different cams (288/280s)? Been doing a LOT of reading about datalogging, tuning, etc.

Mike

Realistically pretty unlikely. Either an engine dyno and a lot of time, or I’d need to daily that setup and iterate for several months. Sorry!

[Bry5on]

Modeled the e46 for fun, now I can do a real analysis of camber, toe and track changes at some point