[John_01]

Fe1rx, Thanks for your comments. It helped me understand what is going on with the subframe bushings. I can now see how the rear subframe bushing compliance is effectively in series with the rear springs, so it makes sense to consider additional movement of the wheel due to bushing compliance as you explained in the post above. I agree there's no change to motion ratios - I was wrong about that.

I think if the wheel rates changes by 10% due to the bushing compliance, then its quite a large effect. For a road car application the chassis engineers will match the front to rear stiffness more accurately than that. I did some calculation on the standard 135i M-sport wheel rates. I was a bit concerned because it seemed the rear wheel rate could be softer than the front when the subframe bushing compliance is added in. To get a decent analysis I need a more complete understanding of the front suspension. In your rear suspension thread, you wrote that torsion of the rear control arm bushings increases the wheel rate by about 35lb/in, but I don't think you have provided any equivalent figure for the front suspension so far. Anyway I'm subscribed to your threads so I will follow with interest.