First, a little bit of the stock
It has been a while since I last drove with stock suspension. Overall, for a street set up it worked quite well on the track. Obviously the springs are soft which means you have to be patient, brake early, and let the car roll into corners. Or, in the words of a racing driver: "you turn the wheel and then a second later you realize 'oh shit' all the 3700 lbs are on the outside wheels."
The other noticeable attribute of the stock suspension is the mid-corner push as expected on most street cars. This is especially noticeable at turn 17/16/15 of MSR Houston. Some drivers will try to stab on the gas to get the rears loose and rotate the car, but during the process you transfer weight away from the front and understeer even more. In sum you lose a lot of time when the car understeers.
Anyhow, onto the main event – KW Competition
I worked with KW and spec'd the kit specifically for a street legal weekend track car. KW has several set up combinations available based on their shaker rig testing and field experience. I chose rates which are about 15% stiffer than their Clubsport. This combination will give the car much quicker transition time vs. stock, and, at the same time, maintain a decent ride on the streets.
First impression is that the turn in is much, much sharper compared to stock. The stiffer springs combined with proper shock valving significantly shortens the transition time which allowed me to brake and turn in later.
Second impression is that there is much more grip in all four corners on the same tires. This is in part due to the front adjustable top mount will give you a max of around -3.5 degrees of camber. I've set mine to -2.8 degrees based on data from prior runs, but I can easily add/subtract if needed -- camber can be adjusted directly through the strut tower openings -- without taking the strut assembly off.
The balance: car is very neutral now at the limit. At turn 2 the carousel you can now be on the throttle for almost the entire duration. And at turn 17/16/15 I can easily get the car pointed at the right direction and power out of the exit.
is my fastest lap time on the stock suspension. 1:45.5
is my time on KW Competition. This is a delta of -2.8 seconds
As you can see from the track data, through every corner the M3 is able to enter and exit at a higher speed. The most notable corner is 17/16/15, where the KW is 4 mph faster than stock. This is due to a much balanced chassis which allowed me to get on the gas pedal much sooner than when the car understeered on stock suspension.
The beauty of KW Competition is that it comes as an integrated suspension solution
. KW has collected a tremendous amount of data on the M3 from KW’s shaker rig testing as well as racing experience, so the kits are truly tested and proven. On the other hand, most high-end dampers from other brands come as dampers only, and typically vendors who may not always have a lot of experience on the M3 are in charge of getting camber plates, spec’ing springs, setting shock valving, etc. Therefore it takes a lot of time and effort to tune a set up like that correctly (for me, I had two racing drivers help me tune my Moton set up).
Hope this has been helpful.