I'm one of the people that had SSL upgrades coil over units for both front and rear units on the 2014 S4 Aero based Plus 8 car I own. Some of the background to this is interesting:I understand that when the Plus 8 was introduced SSL proposed settings for the suspension that was the same as their later developed "kit". A car was built with the SSL recommended springs and suspension units but Morgan engineers rejected it on two main grounds.
First, cost: no surprise as adjustable dual chamber dampers cost more than the ones used by MMC.
Second: the car no longer felt like a Morgan! It seems that MMC chassis engineers want the Aero cars to feel like an evolved Trad, and not like a modern car. So the front and the back are set up to be a bit "disconnected". I've no proof of this, but empirical evidence suggests it could be true. This approach continued on to the introduction of the Aero S5 and the CX cars.
After long discussion with Peter Ballard I asked if SSL could set the car up the way that they originally proposed. The spring rates are what they originally proposed but the damper units are adjustable but not in every way as originally proposed. I've driven about 12,000 miles on the new setup and it is good, the car behaves as a unit, not two ends that want to go their own way.
The brakes. Thg AP Racing 6 piston calipers and matching discs are the best car brakes I've ever experienced. Very little free pedal travel, progressive but ultimately powerful and with a lot of feel/feedback. The level of servo assistance is about perfect. I've tracked the car at Castle Combe. I'm no track day hero and essently "slow and steady", on corners brake in and power out. But amongst hard driven trads I was a lot quicker than I expected because I could apply the brake later and more aggressively without any risk of locking a wheel. The grunt from the 4.8L BMW motor helped a bit getting out of corners, but it isn't a snappy response, especially below 4000 rpm!
So in my view the decision to switch to AP Racing (Brembo) brakes for the 2023 CX series takes them to where they should have been when the cars were introduced. I drove the Plus 6 and Plus 4 when introduced and was highly critical of the brakes, both pedal travel and initial bite.
The Aero Handbrake works on a seperate mechanical caliper on each disc, it is virtually useless and will produce an MOT fail if not prepared for the test. Preparation is to drive the last 10 miles to the MOT place with the handbrake brushing the disc, getting it all good and hot. I've had advisories, but no failure.
