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      10-03-2021, 07:48 PM   #1
ANILE8
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Drives: Z4 M Coupé - Carbon Black
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Rear progressive to linear spring conversion

If anyone is debating this change then I would say do it. The difference in ride quality and compliance is not small, which was a major surprise to me. I was expecting a difference but this highlights just how bad the progressive springs were. If the wife can notice the change, then it is a win.

My coilovers came with re-branded Eibach lowering springs (10mm drop vs stock) and at the time I didn't know enough about the setup to request a liner spring and what height was correct. Fast forward a few years and I finally got around to making the change.

From much discussion in other threads, for the rear I purchased Hyperco 5"/500lbs springs, (front I am using 400lbs). I decided to use a helper spring because I was concerned that they might dislodge at full droop. As it turned out they were probably not needed but they do make the install easier and give me an effective spring height of 5.5" which puts my adjuster right in the middle of it's range. They provide a maximum of about 2.5" lift. More on that later. If you are not using helpers then the adjuster would be have been right at the top of it's range for my given ride height.

I choose R/E articulating perches as my preferred height adjuster. GC make a similar unit which I'm sure is just as good at a little cheaper cost. I will say the R/E locating cones did need a little modification to fit our vehicles. A few minutes with a Dremel will fix this.

Another benefit is the weight saving. The progressive springs weigh a massive 6.6lbs each! The hyperco stuff plus the R/E perches would be around a thrid of that.
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