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Discussion Starter #1
Is it necessary to pry off the wheel center caps with the MB star when driving the car on track events/autox's near or at the limit? SLK55er, did you yank yours? I'm concerned because I've had this issue on my audi where my center caps would fly off at track events during hard cornering causing twisting of the wheel etc and I've lost several caps that way. Not sure of an easy way of prying off these MB center caps though. Also, any advice on what kind of cold tire pressures to run on autox's as compared to road courses where most maneuvers are tighter and generally more demanding in terms of tire grip and wear?

So autox season is here and I plan on running on at least 4-5 events this year hopefully... and I can definitely kiss these stock pirelli rosso's goodbye by summer's end. Looks like the SLK55 will run in Class A Stock http://moutons.org/sccasolo/Lists/2005/stockc.html while the SLK350 will be B stock. Stiff competition the SLK55 has... up against M coupes, NSX's, S2000's, AWD WRX STi's, and AWD Audi V8 S4's. Yikes.
 

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Those caps are very difficult to pry off...

I know, coz my old SLK had the Brabus ones, and the only way to remove them was to first take the rim off, and then hit at it from inside in order to nudge the (rather hard) metal rim that keeps it in place, out of the slot and off the rims.

I wouldn't really worry about it, honestly, I've never even seen an MB where that center cap was missing (unlike with some other models of car).
 

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'14 CLS63 AMG S, '10 GLK350, '03 SL5000
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Shinigami - 3/24/2005 2:59 AM

I wouldn't really worry about it, honestly, I've never even seen an MB where that center cap was missing (unlike with some other models of car).
I agree with Shinigami -- I ran very hard for over 2 hours on the track and had no problems with the center caps due to stresses or heat. I've removed BMW plastic caps many times, but I don't think that is necessary with the SLK55's wheels. If you do, I also suggest that you pop them out from the inside after removing the wheel rather than trying to pry them off with the wheel on the car.

WRT cold tire pressures (and EDC switched off via the dash button), I recommend that you start with 36 psi front and 34 psi rear. You may find that a few psi more in the front is a help to reduce understeer, but with the V8's torque, you'll be able to overcome that with the throttle. As and experienced autocrosser, you'll be able to tell from there what adjustments to make. You probably know to mark the outside sidewalls with a tire crayon to easily determine how much the tire is rolling under the wheel in hard corners.

BTW -- I was amazed how little brake wear I had during my track time on a pretty tight track -- only a 32nd or so of wear! Since I had no track experience with the SLK prior to that event, I took a set of brake pads with me in case they wore excessively, but I'm glad to report that there was so little wear. (I'll make a post on How To Change Your SLK55 Brake Pads. If you need this info soon, please let me know and I'll provide what help I can.)

You may have read that I was disappointed in the usefulness of Manual Mode for track events, but with autocrossing, this may be very helpful since I assume you'll probably run mostly in 2nd and possibly 3rd, depending how tight the course is. I'll be curious on your experience with the transmission modes.

Hope you have a very successful and enjoyable event. We look forward to your report.
 

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Discussion Starter #4
Thanks for the excellent advice. Tell me more about this tire crayon thing... although I like to attend autox's, driving schools, and other track events, I admit I'm not very thorough when it comes to attending to details about tire wear, etc. I'm mostly in it for kicks and not the competitive side. That isn't to say I don't desire to learn more about my car, because I do. That's why I find your posts very entertaining and immensely informative. I wish I had even half as comprehensive an approach as you do. So it turns out I can't attend this season's first event in April but I will surely let you all know how the May autox goes.
 

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masmole - 3/24/2005 12:12 AM

Tell me more about this tire crayon thing
Hi again, masmole. There is nothing here very complex or sophisticated, but it's a good place to start and easier to do that trying to just look at the tire wear on the outside edge.

You can probably get a free yellow or white tire crayon from your local tire shop such as Goodyear, PepBoys, etc. or find a crayon at your local hardware store that will work. A Crayola crayon that a child would have will not really work that well, I don't believe -- it needs to be softer and adhere to the rubber.

The idea is to mark the outside edge of each tire with a radial line, say 2 inches long, that starts on the tread and continues outward onto the sidewall and inch or so. Then as you drive hard through the corners, you can see how much of the line is worn off and how much the tire is rolling under.

The idea is to put in enough pressure so that the sidewall is not being worn excessively, but not too much such that only the flat part of the tire tread is being used. A small amount of wear on the edge of the tire would be the goal.
You can learn a lot just by going out to a remote parking lot somewhere and running in circles at increasing speeds, making your own skid pad.

There are a lot of variables; each tire is different with different sidewall and tread design, but at least you can use the info from this simple method as a reference, perhaps even to determine how sensitive the tire is to pressure changes.
 
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