Thanks for the writeup on these coilovers. I've been interested in seeing people's impressions of Sachs/Eibach's kit.
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Originally Posted by x233
Still, getting the right height is a tricky part because of the limitations of the coilover kit per se, and because it’s hard to judge the exact lowering immediately after adjustment. It takes a while to settle.
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One thing to consider about when adjusting the height is the spring to wheel motion ratio. This means for every Xmm of wheel travel there's Ymm of spring travel/compression. When I'm dialing in my ride height I usually measure how much I want to lower at the wheel, and then calculate how much that equates to at the spring. This typically gets me very close to the actual setting.
Quote:
Originally Posted by x233
Front spring is progressive, rear is linear
Front axle spring rate: 48 N/mm (pretty sure both front and rear are softer than the stock)
Rear axle spring rate: 120 N/mm
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The front is a good bit stiffer than the F87 OE springs, but the rear is similar (slightly stiffer). It looks to me they aimed to make the front and rear ride frequencies equal to each other instead of maintaining a flat ride ratio that the OE suspension had where the front frequency is lower than the rear.
Going to flat ride would probably help your high speed stability issues since the chassis would settle faster. With a pitch/non flat ride frequency setup you have to rely on higher damping (overdamping) to keep things under control. Your own experience shows this when you mentioned at higher speeds you have to turn up the damping settings (which then hurt ride quality too much).
If that's something you want to play around with in the future you can try putting different stiffer springs in the rear. Sometimes coilover kits can accept standard 60/65mm, 2/2.5" coilover springs, or there are cheap enough adapters to use them with.
Here's a video where we changed the springs on a Bilstein B14 kit to produce flat ride. The original springs had a higher front ride frequency than rear.