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The rear springs have these aluminum adjustable seats to make the ride height adjustable. These slip over the stock spring perches The seats are hard anodized for corrosion resistance. 
The rear damping adjuster is on top of the shock shaft.
The stock Fiesta ST rear suspension uses a twist beam. Don't be fooled, although a twist beam sounds crude, it actually works really well in practice and several good handling FWD cars before it have been equipped with twist beam rear suspension.
The stock rear spring is held in place by the rear shock.
You unbolt the rear shock and let the twist beam hang. The spring pops right out. Pretty darned easy.
The Suspension Techniques rear shock is shorter than stock so the car can sit lower without losing bump travel when lowered.
3 comments
What class is this being built to “race” in? Asking because I noticed you did not go as large of a brake kit as I would have thought (or that we went to) to truly upgrade the system. And I don’t see any brake venting. Are you not having heating issues with your brakes? We put the Wilwood kit on my son’s ’16 and are now working on ducting for it. After melting the stock caliper seals and dust boots twice, he decided to go with a larger rotor and caliper that gives him much more pad area. I must say I love the new brakes. Let just hope they last better then the factory ones did with Hawk pads.
At the time, there were not any other alternatives.
I am really glad I found all your articles on Fiesta ST race build as I am building an ST for rallycross here in the UK. Lots of great tips and things I hadn’t considered before. Thank you.