Just figured I'd post a long term review of the Swift Spec R & koni yellow combo, which is highly regarded on here.
The idea behind this post is to document my impressions, thoughts, problems and solutions to these problems.
Car is a 09 E82 135i with stock 261m wheels running 225 tyres up front and 255 tyres in the rear, shocks are stock koni yellows up front and TCK line externally adjustable rear shock with a 1" shorter shock body (more on this later).
Immediately apparent when sitting in the car after install was the reduction in ride height. Also immediately apparent to me was what felt like there wasn't enough shock travel up front (FWIW I am running stock bump stops up front). Even from day 1 I never considered myself entirely happy with the setup, but it was still an improvement over 90k km old OEM dampers.
Also worth noting is that the softer spring rate of the front Spec Rs results in a tendency for understeer - This was drastically improved by adding in a m3 front sway bar.
After 12 months or so the I began to notice the rear ride height had been visibly reduced from the initially installed height. After digging up some old measurements I discovered that that rear had lost about 15-20mm of ride height on top of the 25mm or so drop from stock.
This presented 2 issues :
1) I wasn't able to achieve suitable rear camber settings (adjuster became maxed out).
2) On a spirited drive I ended up wearing a hole through the fuel filler neck from the tyre rubbing on it - Only an issue on fast big bumps, normal street driving for over a year and the issue never presented itself.
Problem number 1 - I had two options to rectify either raise the rear ride height or install adjustable control arms
Problem number 2 was cured by replacing the dinan rear shock mounts with monroe shock mounts and installing 8.5mm of bump stock packers to lengthen the shock body and limit how much the suspension can compress (note this is in addition to the 1 x 2.5mm bump stop packer that comes with the TCK koni shocks).
The solution to 2 resulted in a noticeable deterioration of ride quality but resolved the fuel filler neck rubbing issue.
In order to address the main issue (rear ride height) I reached out to Swift and they assisted by sending out a replacement set of rear springs at no cost to me.
. Unfortunately this was short lived as within 6 months the new springs had begun to sag once again.
. Fortunately for me I discovered that BMW made a kit known as the rough road kit which is basically a 5mm spacer for the spring (increasing the ride height by approx 9mm or 5mm divided by the rear motion ratio). I persisted with this setup for another 3 months or so but the ride height was still too low for my liking and the rear noticeably crashed on sharp bumps - something I had previously attributed to the firmer rear subframe bushes installed.
Now on to the front.... After 2.5 years or so and something which I had not realised was that the front springs had also sagged (although to a lesser extent - 10mm or so compared to measurements from 3 months after install). Upon looking at the front springs in situ there is clear evidence of binding marks on the springs as well as markings on the lower spring mount on the shock.
FWIW measurements measured from bottom of the rim to the body were as follows (after 2.5 years of service):
Front - 565mm with dinan camber plates
Rear - 570mm with rough road kit
Remove the rough road kit and the dinan camber plates and clearance would be a huge issue making the car virtually undrivable on anything but smooth roads.
Photos to follow.