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'14 CLS63 AMG S, '10 GLK350, '03 SL5000
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On Sunday, March 6th, in Pahrump, Nevada, 60 mi west of Las Vegas, I had the opportunity to run my SLK55 on the 2.2 Spring Mountain Ranch Racetrack with about 25 other really nice cars. (See the track map and www.lappingdays.com for more info on this event.) This was a "Getting To Know You" opportunity for me to experiment with the AMG's transmission, tire pressures and EDC and to appreciate the car at speed on a road course. My real objective was to gain confidence in the car and with my ability to exploit at least some of the AMG's potential before running in May at Pikes Peak International Raceway with my BMW Club and racing friends in Colorado.


This "lapping day" allowed me to run 125 miles on the track in half-hour sessions for a total of about 2.5 hours (and averaged 7.1 miles per gallon.) I discovered some very interesting quirks, strengths and limitations of the car. And -- nothing new here --confirmed that the AMG is generally more capable than it's driver.

CONCLUSIONS (nothing dramatic -- you can read further details below if interested):

Overall the car is a joy to drive on the track.
Stock street tires really limit the cornering ability.
Tire pressures should be in the 34-36 psi range (surprisingly low to me.)
Run in Sport Mode with EDC off -- forget Manual Mode.
Use the steering wheel buttons to downshift approaching the turns.
Brakes are incredible -- no problems with fade or rotor warping.
Exhaust note turns heads.
Don't forget to press the Air Conditioning OFF button while on track.

BACKGROUND:

Please forgive me for mentioning my background, but to provide some credibility for my comments, let me mention that I have over 8,000 miles of on-track experience over the past 22 years and have run most of the major tracks in the USA. My racing handle is "Mr. Smooth." I've been a driving and classroom instructor with the BMW Club for a very long time and have held an SCCA Pro License. Highlights include a "fastest lap in class" and 3rd place finish at Sears Point in an Escort World Challenge race (E30 M3.) I also have had the thrill of an 11/10ths ride in my own AWD BMW 325iX driven by The Derek Bell at Sears Point. Lowlights include a high-speed spin and contact with the wall at "The Kink" at Road America in a Spec Renault/Racer. Yes, one learns from one's mistakes!

THE TRACK AND THE DAY:

I ran the 1st half-hour session very conservatively with the EDC on and with the transmission in Sport mode, refreshing my memory of this track. The 2nd session I ran more aggressively and started playing with the transmission and EDC. At the end of this session, I took some tire temps and discovered that I had way too much tire pressure. (I'll make a separate post on that issue with some data.) Later in the day, I was pretty much able to put it all together and get some very nice lap times.

Top speed that I saw was 112 mph down the back straight before braking for the 3rd gear Turn 8. The 540 hp Porsche Carrerra 4 (I'm not really familiar with the Porsche models, but I believe that is correct.) and the Dodge Viper claimed 130 mph. Then down into 2nd gear for Turn 10 and accel to 85 mph before braking hard for Turn 1. Then into my favorite part of this through the "S" in Turns 1 and 2 which I ran at around 60 mph. In this "S" one is really able to steer the car with the throttle after setting the suspension -- lift off slightly and the car pitches forward a bit, loading up the front tires and inducing slight oversteer. Add a little throttle and the opposite occurs -- the car straightens out with a bit of understeer. So through the middle of the "S" one accelerates a bit and the car naturally sets up for Turn 2 This really is fun!

The most difficult part of the track was Turn 4 because I really never did figure out the best line and best gear (2nd vs, 3rd) to accelerate up the hill in this increasing radius turn. The V8 had enough torque to just use 3rd, but it was very tempting to blast out of there in 2nd -- sounded really nice, but probably no quicker. I backed off a bit down the hill through the most exciting and dangerous part of the course, Turn 6. Turn 7 was another question of 2nd or 3rd gear like turn 4 -- accelerating out in 2nd felt good, but by eliminating the 3rd to 2nd downshift and being on the proper line, 3rd was probably just as quick given the V8's torque.


So enough about the track. Here are my comments about the SLK55:

SO HOW WAS THE SLK?

I'll expand on these comments, but overall, I'm extremely pleased with the car. Straight line performance is, as expected, pretty awesome. Cornering is limited by the tires. No complaints about the steering. The 7G automatic is just fine -- upshifts are extremely quick and, downshifts and the steering wheel buttons take some getting used to. Turn the EDC off -- there is still some intervention even with it off, but it is helpful in avoiding unnecessary tire wear. At least a dozen people told me how incredible the exhaust sounded accelerating out of 2nd, into 3rd and 4th past the Paddock.

Lap Times:

Although this was not a timed event, I did manage to take a couple of typical lap times for some of the faster cars:

Porsche GT3 2 minutes even race compound tires
BMW E46 M3 2 minutes, 2 sec. race compound tires, current M3
My Good Laps 2 minutes, 4 sec. street tires
Porsche Boxster 2 minutes, 15 sec. street tires, relatively new driver
Viper (estimate) 1 minute, 55 sec. how do you spell Torque?
SR3 Race Car 1 minute, 50 sec. 1200 pounds, what corners?


Tires:

The Pirelli P-Zero Rossos are a limiting factor in the turns. Although they are a great choice for spirited driving on the street, their tread has a lot of open space and is only about 60% rubber. Most of the serious drivers towed their vehicles and had separate track wheels and tires which are 95% rubber and provide much more grip. With stickier tires, IÕm sure that I would have picked up a couple of seconds run with the fastest M3s, but probably not the GT3s.

I still have some more testing to do, but I was surprised to find that it is not necessary to bump up the tire pressure to preserve the outer edges of the street tires (which unlike track or race tires have a lot of grooves.) Typically on the BMWs that I've run on the track, it was necessary to put 40-42 psi in the fronts to save the outside edges of the front tires. IÕll make a separate post with pyrometer data, but for now, I'll say that I started with 42 psi and found that the INSIDE of the SLK55's front tires were hot! Also, with 38 psi in the rear tires and the EDC off, there was a noticeable increase in tire temps on the inside. Next time, I'll start with 36 psi (cold) all around and and go up or down from there.

G7 Transmission Manual Mode:

I may be missing something, but Manual Mode in the G7 transmission is pretty much useless on the track as well as on the street. If the transmission really held in the selected gear, then that would be OK, but it seems to upshift and downshift by itself. Consequently, one never really knows what gear it is in without looking at the display which is often obscured by the steering wheel in the turns. Plus downshifts are too slow and one cannot click the steering wheel button, say twice to shift from 4th to 2nd without waiting for 3rd to engage. Simply holding the button in only seems to yield a one-gear downshift, even if a lower gear would be acceptable. (On the street in normal driving, I was surprised and disappointed that it is even worse -- it downshifts by itself into 1st at a stoplight! How 'bout a truly manual mode?)

G7 Sport Mode:

I finally got comfortable and pleased running in Sport Mode and using the steering wheel buttons to downshift for the turns. For example, Coming down the back straight (Turn 7-8), the transmission would be in 4th gear under full throttle. As I started braking in a straight line for turn 8, I could tap the button and get into 3rd gear without upsetting the balance of the car or causing the rear wheels to lock. (That is difficult to do with a manual transmission without double clutching and a smooth heel-and-toe.) Then I could tap again just before Turn 9 to get into 2nd to accel briefly between 9 and 10 and then be set up to blast out of 10 in 2nd. IÕd be into 3rd and then into 4th before turn 1 but another tap on the button gave 3rd gear to run all the way through Turns 1 to 4. Thankfully it would hold in 3rd, even though I was feathering the throttle at times to steer and balance the car. Sometimes I would get 2nd gear out of Turn 3 and 4, depending on how aggressive I was with the throttle, but it would upshift into 3rd for the tight downhill kinks into Turn 4. Another click into Turn 5 yielded 2nd gear if I felt it was needed, but as with several of the tighter turns, the V8's torque was adequate to pull out of the turn if I was on the right line.

EDC:

With the EDC on, it is easy to stay out of trouble and this is a good way to spend a 1st session, particularly with a wet track and cold tires. But the intervention of the EDC in backing off the throttle leads to unnecessary disruption. It really is effective in reducing rear tire wear, however -- more on that in a separate post. By pressing the EDC OFF button, there is just the right amount of involvement. It is still possible to slide the rear a bit, but if one really gets over the limit where there is no benefit (except to your tire retailer), the EDC backs off the throttle a bit. I see no need to turn the EDC off completely unless one is participating in a Drifting Event.

MISCELLANEOUS:

I had not realized that the Air Conditioning is normally ON or available to come on automatically when the Climate Control is in AUTO Mode. (In my BMWs, the AC is normally off and one must press a button to turn it on, even in AUTO Mode.) So, don't forget to take the system out of AUTO and press the A/C OFF button.

Suggest you find a wide-angle clip on mirror for the inside rear view mirror (to help see traffic at all times, not just while on the track. Also, a small wedge blind-spot mirror on the outside driver mirror is very helpful.)

Some (magnetic removable) flames on the side of your SLK are good for a couple of seconds a lap.[}:)]



Hope you found this interesting and helpful. Enjoy your SLK on the track!
 

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2005 SLK350 2011 GLK3504X 2006 ML350(selling when GLK arrives)
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Incredible post...enjoyed it...thanks...[;)] [:D][8D][:D]

BTW - a closer pic of your SLK with the flames would be cool...[:D]
 

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This was one of the most enjoyable postings that I have read on BenzWorld. Thanks for sharing your experience with us. I also think it was a good idea to give your backround as it adds a lot of credibility to your comments. I'll look forward to more of your postings.

Mel
 

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Great post and do you have more photos?

slk55er - 3/8/2005 5:53 PM

Viper (estimate) 1 minute, 55 sec. how do you spell Torque?...
You spell it: Viper[:D]

slk55er - 3/8/2005 5:53 PM
...I had not realized that the Air Conditioning is normally ON or available to come on automatically when the Climate Control is in AUTO Mode. (In my BMWs, the AC is normally off and one must press a button to turn it on, even in AUTO Mode.) So, don't forget to take the system out of AUTO and press the A/C OFF button.
You can leave it in auto mode just cut off the AC by hitting the AC button. It will always stay off (even after restart) once cut off unless you cut on the defrost and then it will go off when you switch back to auto.
 

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Great post mate. Thoroughly enjoyed reading it.

cheers
roadsta
 

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EXCELLENT POST!!!!

Nice to hear your comments about your track day.

an you post something similar about your every day driving on the road and how the 55AMG handles there.

I currently have the SLK350 and find the ESP light is always flickering when cornering even at 40.....
I am taking delivery of my 55 AMG in MAY and wanted to know of your street experiences.
Thanks
Shry
 

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Discussion Starter #9
Thanks -- a few more comments

Thanks for the interest in my post.

Sorry, I do not have any more photos from the track day -- too busy with driving, taking tire temps, and socializing with the other enthusiasts. I'll take a couple of photos of the car with the flames. They always go on for track events -- a gift from one of my racing buddies who is now a VP in the BMW Club.

I did measure the brake pad wear for the day and was astounded and really pleased to find that I only lost about 1/32 of pad. That is excellent -- I've gone through a complete set of EBC Red pads during a 2-day school at Laguna Seca. The more I drive this car, the more impressed I am.

WRT street driving, I am equally pleased -- very comfortable and a surpising amount of trunk space, really. In Sport Mode, 1st gear starts are a bit harsh for casual driving around town, but that Comfort Mode is perfect for that. Someone once said WRT moving through traffic in an M3, "You want go go there? No problem." Well that certainly applies even more so to the SLK55 -- no problem! As I've said in prevous posts, even if a manual transmission were available, I would still opt for this automatic bacause of its performance and convenience. -- even if the Manual Mode is pretty useless, and now especially so after having it out on the track.

BTW -- on one of those 4-mile-long stretches of Nevada highway where there is nothing in sight except sagebrush, I took the 55 to it's speed limit for a few seconds. It topped out at an indicated 158 mph before the limiter did it's thing. It seemed to get there effortlessly and there was not a hint of any turbulance or floating.

One thing that I wish for (and it may be there and I've just missed it) is a "one-touch" seat reposition function when the ignition is off (like my 740i has) such that no matter where the seat is, one can simply touch (and not hold) any of the seat buttons and the seat will go to that positon.

Another is that I wish there were a more convenient way to jack the car with a floor jack and set it on jack stands. I have figured this out and will make a separate post on this, but it would be nice to have built-in rubber jacking pads like BMW provides.

Two more things -- I did add a metal dead pedal for my left foot to keep the carpet from wearing (used one of the good matching pedals in a $20 pedal set from Autozone and attached it with velcro.) Also, I made a dipstick to actually check the oil and I'll make a separate post on this.
 

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slk55er - 3/9/2005 10:53 PM

I may be missing something, but Manual Mode in the G7 transmission is pretty much useless on the track as well as on the street. If the transmission really held in the selected gear, then that would be OK, but it seems to upshift and downshift by itself. Consequently, one never really knows what gear it is in without looking at the display which is often obscured by the steering wheel in the turns.
Talking to my MB mechanic he says that even in Manual or Automatic mode and using the shifters the car will never allow you to cause damage to the engine. In other words the car is going to always be controlling the gears to some degree.

Love the article BTW.
 
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