Good ways to reduce the unsprung weight

[Eric]

Indeed. On the front, it's easy to identify what is sprung and what is I sprung. But on the rear... Is the subframe u sprung? Trailing arms?

No plans, just something I ponder.


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[Wh33lhop]

Actually both trailing arms and control arms are effectively semi-sprung. Got a minute? Siddown.

This would be a lot easier to explain with some visual aid but I'll do my best without, apologies if it's confusing.

For the sake of simplicity, let's assume the subframe bushings are solid and the subframe is affixed to the chassis--the trailing arms would be effectively semi-sprung. The portion of the trailing arm attached to the subframe--at the bushings--would be sprung as it's affixed to the chassis and wouldn't move at all throughout the suspension stroke. The portion at the spindle will move as much as the wheel (that portion by itself would be unsprung). The portion halfway between the two would move half as much, making it effectively half sprung. So it winds up acting as about half sprung and half unsprung--you'd have to know the mass density over the entire arm and do a weighted integral to figure out exactly how much is contributed to both.

In that same light, everyone assumes control arms are fully unsprung, but half of the control arm (the portion from the CAB to the subframe) doesn't move at all when the front suspension goes through its stroke, the other half (subframe to spindle) is a lever like the trailing arms. So I'm officially guesstimating it would only act 1/4 to 1/3 sprung. Those pricey M3 control arms, while they're 4lbs lighter, only effectively remove around 1lb per side of unsprung mass by my shitty estimation. It makes a difference but not a huge one, and I'd say the beefier ball joints are probably of more benefit. Sorry 2man :p