BMW e90 M3 LSL - Suspension
One hundred and thirty thousand miles on OEM shocks, bushings. Some of that with lowering springs installed by a previous owner. Time for a change.
The factory shocks with the lowering springs feel bouncy, with too much rebound or shot compression or just too much wear. The car crashes and rolls and just soft all around. To solve those problems the vehicle needs better bushings, better shocks and springs and better sub frame mounting.
With a wide variety of systems available I chose to work with MCS. Their shocks performed extremely well on some other builds with being very responsive, tunable and of high build quality. The valving works great and each adjustment has a significant change, impacting the overall feel. I did not want to deal with external reservoirs as the car would not see racing conditions to justify the components. Keeping in mind the goal of the vehicle and the LSL mentality - the setup had to be similar closer to what an OEM might come up with for a special model.
MCS offers the 2WNR shocks - which are 2 way adjustable (rebound and compression). The adjustment mechanism is quite unique in that the same little knob will do both, depending on position. You can click the knob down for one adjustment and release it upward for another. Easy.
The shocks are paired with Swift springs with front at 504lbs, with 168lbs helper and rear at 784lbs. This should provide enough compliance for roads and rougher tracks but also support the chassis well. Ground Control Race camber plates will secure the assembly along with their pivoting rear spring perches. The rear perches will pivot as the suspension travels, keeping the spring more square and not skewing the rate.
With better chassis control - need to ensure that there is minimal flexibility. Bimmerworld has a very comprehensive catalog of components to eliminate rubber and create a more direct chassis.
The rear subframe gets solid alum bushings along with the differential. Also eliminating the subframe side camber arm bushings in favor of nice sealed monoballs. The trailing arm bushings get replaced with a similar bushing. Also updating the front control arm rubber bushing to a monoball setup.
Bimmerworld uses nice sealed OEM like monoballs which will go a long way with reducing noise and increasing longevity. Monoballs are reliable and strong but most of the time they are exposed to the elements and wear prematurely - its not as relevant in motorsport due to increased service interval and more controlled conditions. BMW already uses monoballs on some suspension arms and I am merely finishing their job. A Porsche GT2RS (or 3RS ) does not have a single rubber bushing in the suspension, running the same sealed monoballs everywhere.
Im also adding adjustable drop links to aid in corner balancing the car (and the OE units are long dead) along with toe links. Ill address the bushings in the rear control arms at a later time if they prove to be too flexible.
One helpful note before installing coilovers is to measure the current ride height. This helps when resetting the car up, as you end up back in the ballpark of the alignment. This gives you the ability to use the car and have it drive more or less straight if you need to take it somewhere.
Getting new parts is fantastic, but installing them can be a “ride”. The rear subframe bushings are a real challenge. I decided to yank the subframe out with a friend, which was relatively easy. Using a press along with a lot of adapters and cylinders I got the bushings out, installed the Bimmerworld solid units. By the time that was done, we just wanted to get the thing back into the car.
I opted to do the rear monoballs, toe arms and diff mounts another time - for I could do those myself. Instead, we threw in the coilovers and set the car to previous ride height and camber. The trunk lining prevents easy access to the rear shock tower and over the tower itself was a rubber cover. I punched a hole in the trunk lining with a holesaw and re-used the rubber cap for a clean install. Easy access and looks intentional. The rear Ground Control spring adjusters are quite useful. Ride height tweaking is a breeze with easy tool access and a very effective design as the area is already so tight withouth easy tool access. No need to remove the wheels!.
Once the rear suspension upgrades are done, I will then corner balance the car and do a full alignment.