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Premium Member 2007 SLK55 AMG
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806 Posts
Discussion Starter · #1 ·
I've posted about my car before but I figured I'd start a thread to share my experience with driving an SLK55 competitively in autocross and circuitcross as well as HPDEs (High Performance Driving Events / Track Days.) Maybe others looking to hit the track can benefit from my experiences.

2007 SLK55 w/ P30 Package

Current mods:

Suspension
BC Racing Coilovers - The only coilover setup for the R171 with front camber plates
Lowered 19mm all around from stock clearance (from MB dealership alignment print out)
Camber: -2.5 degrees front (-1.2 is OEM spec), -2 degrees rear (-2 is oem spec)
Toe: Currently 0 all around

Brakes
Porterfield R4-S Brake Pads
Motul RBF600 Fluid

Wheels and Tires
Enkei PF01: 18x8 front, 18x9 rear (ET35 all around) - Approx. 10lbs lighter per corner than OEM wheels.
245/35/18 Front, 275/35/18 Rear - This size matches closest to the OEM tire diameters while being significantly wider
With my car lowered as much as it is, there is some slight rubbing at the top of the felt fender liners in all corners, but nothing to be alarmed about. This only happens in full compression during elevation changes at the track. It has not damaged the tires or the fender liner itself, just the lining.

Engine/Exhaust
Secondary Cat Delete
Custom X-Pipe
Stock Mufflers
aFe Pro Dry S Filters
Eurocharged Tune (without rev limiter increase for safety)
I constantly get compliments at the track for the sound of this car. It sounds great with this setup, loud on throttle, but quiet when driving normally.

Future Mods:
Racingbrake Lightweight 2-Piece Rotors
Racingbrake XT910 Street/HPDE pads
Racingbrake Stainless Steel Brake Lines
I've had the Racingbrake setup for a few months and have been waiting for the warmer weather to install them. They should reduce unsprung weight by about 3lbs per corner. Another advantage with the RB rotors is that they sell the friction disks separately, so you can reuse the rotor hat and buy only the replacement friction disks which saves a lot of money in the long run against the expensive OEM rotors.
Not yet purchased:
Needswings Oil Catch Can
Needswings Intake
Lightweight Braille Battery (pending corner balancing results)
LSD of some sort
SWIFT front spring upgrade, possibly slightly stiffer
Polyurethane Bushings - There is no kit, but I plan to research the individual sizes in order to come up with a kit myself using universal bushings


Driving Impressions
With my current setup, the car feels very well balanced and neutral. Turn in is point and shoot, and is very easy to rotate mid corner with lift or trail braking. Any oversteer from lift or braking is easily controlled. When stock, there was some push mid corner but a little more stiffness and negative camber has helped this. Easy to straighten with power at the exit as well. It should be noted that I drive with the top down. I find the car to be better balanced with the weight of the room tucked in the trunk rather than being up high. Lower center of gravity and more weight in the rear for traction and to counter the weight of the motor up front.

I have not driven on track with stock brake pads and brake fluid, so I cannot comment on that or recommend it. However, Motul RBF600 fluid and Porterfield R4-S pads perform well with repeated 30-minute sessions at all the tracks at Summit Point and at Virginia International Raceway. My Racingbrake setup should be just as good, if not better.

Power is adequate for the track. Any more would make it more difficult to drive and would be taxing on the already limited tire width of the SLK. That's why I am avoiding the urge to get some headers for more power. Besides, I enjoy driving the car on the street once a week or so and don't want it to get too loud. I drive with the transmission in "S." but click the paddle down to "1" before setting off. I generally let the car shift on its own and it does a good job, but I'll manually downshift an extra gear in some tighter corners depending on the track - then leave it alone again for the rest of the lap.

The car is competitive (at least in local environments, not nationally.) in its class. It's a relatively heavy car and I have not removed any of the creature comforts like heated seats, air scarf, etc. I have placed consistently in the overall top 5 in SCCA autocrosses with 90-100 drivers as well as lapping similar times to Caymans, 911s, Corvettes, etc.

Future Plans
I want to get the car corner balanced soon. The car should be well balanced left to right, so I don't want to upset that by replacing the battery with a lighter unit. I also want to see if I can move up to a 255/35/18 in front. It's not necessary though as I feel the front grip is fine, and is lacking more in rear grip if anything. Maybe look into an aftermarket differential.

I keep going back and forth on stripping the car down for weight... but I was just driving around in 16 degree fahrenheit weather with the top down the other day and I just know I'd miss the heated seats, air scarf, a/c, stereo, etc. It would be quicker on track, but I think I'd lose too much by stripping it down. I may consider stripping some of the sound proofing and lining in some areas though.

Video

Pictures




 

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Premium Member 2007 SLK55 AMG
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806 Posts
Discussion Starter · #2 · (Edited)
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Registered 2006 SLK55 AMG
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253 Posts
Thanks for sharing your (very enviable) setup and compiling all your research in one convenient location!

With the wide rubber, extra front camber and zero toe-in do you find the car tends to tramline and follow road cresting when driving on the street?

tn
 

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Premium Member 2007 SLK55 AMG
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806 Posts
Discussion Starter · #4 ·
On the street, the car feels like stock - just slightly stiffer because of the higher spring rates on the BC Coilovers. The damping/rebound is adjustable in 32 increments, so I have them on the soft side on the street and more on the stiff side on the track. It doesn't get affected by bumps on the road or anything like that.

Without the increased negative camber in front, the outer edge of the front tires get worn very very quickly.
 

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Premium Member 2007 SLK55 AMG
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806 Posts
Discussion Starter · #5 ·
This is what brand new Michelin Pilot Super Sports look like after 2 track weekends and about 2000 miles on street look like with stock front camber, before coilovers. The outer edge of the tread pattern is completely gone. This is even with the air pressure abnormally high in front to compensate. Less front grip and lots of excess wear.

The horizontal tread pattern should continue all the way to the edge, but it has been worn down completely.

 

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*Registered
2007 SLK55 AMG
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40 Posts
Hi Mark

I have read your post with interest regarding the BR coilovers. i am thinking about getting these for my 55 AMG. When you mention the negative camber wearing the front tyres - how do you adjust this to stop this happening?

Can i ask the part number for the BR coilovers and did you have any issues installing them, how easy is it to adjust the dampening control?

Any advice would be greatly appreciated.

Andrew
 

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*Registered
2007 SLK55 AMG
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105 Posts
Mark,
Are you using the 6k/11k springs that the bc coilovers come with, or did you have them increase the spring rate on the front springs to deal with the heavier 55 motor?
Sorry to bump this old thread but im interested in the answer on this as well as im planning to get a set as well for my 55.
In the uk you have the option to get custom spring rates. They have an option for 12/11 for example which seems to be perfect for the heavier nose of the 55 :wink:
 

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Founding Member 2006
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108,881 Posts
Sorry to bump this old thread but im interested in the answer on this as well as im planning to get a set as well for my 55.
In the uk you have the option to get custom spring rates. They have an option for 12/11 for example which seems to be perfect for the heavier nose of the 55 :wink:
Hi! You said 'for your 55'

Do you have a 55?

your profile says

Vehicle: looking for 55

Please update your profile if you now have a 55...model and year Thanks
 
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