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.

[nuc1]

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

[George Hill]

2) Tonight's realization after modeling the e46 rear suspension: The e46 suspension is just a semi-trailing arm suspension that accommodates camber and toe adjustments. It's really just an evolution of the e30 and prior designs. Suspension behavior is much more in line with a semi trailing arm than a multi-link suspension due to the placement of the members. Can't believe I hadn't realized this until now, duh.

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?

[heinzboehmer]

2) Tonight's realization after modeling the e46 rear suspension: The e46 suspension is just a semi-trailing arm suspension that accommodates camber and toe adjustments. It's really just an evolution of the e30 and prior designs. Suspension behavior is much more in line with a semi trailing arm than a multi-link suspension due to the placement of the members. Can't believe I hadn't realized this until now, duh.

Looking from the bottom of the car, the lower dashed line in this picture depicts the axis of rotation of the 'trailing arm' as the instant center is basically stationary throughout suspension travel:

Woah, mind blown.

[Bry5on]

A few things:
1) Euro Mullet tune v26 seems to be on the money now. I'm happy with cold start operation and a couple days in it still seems to be butter smooth everywhere in the rev band. More seat time to come, but hopefully this is the last rev

2) Tonight's realization after modeling the e46 rear suspension: The e46 suspension is just a semi-trailing arm suspension that accommodates camber and toe adjustments. It's really just an evolution of the e30 and prior designs. Suspension behavior is much more in line with a semi trailing arm than a multi-link suspension due to the placement of the members. Can't believe I hadn't realized this until now, duh.

Looking from the bottom of the car, the lower dashed line in this picture depicts the axis of rotation of the 'trailing arm' as the instant center is basically stationary throughout suspension travel:


3) The hubs are slightly rearward of the diff output flanges, about 20-30mm. This is probably to keep from passing the CV joint through its center axis position if I had to guess.

4) There is quite a lot of anti-squat in the e46, but we already knew this. Wheel hop!