I have been doing a little research on spring and thought I would share what I have found out so far. Currently I am running stock springs that have been cut by one coil all the way around with the bump stops in the rear trimmed almost in half. The car rides pretty much like stock which isn't all that great. The issue I was having was when I hit larger bimps I was getting planted pretty hard into the seat and the wife never like the ride to begin with. I switched to KYB Gas Adjust shocks and the the problem with bumps is gone and the car feels much better on rough roads. the car handles better and corners much flatter. The KYB's are firmer than stock and now feels too stiff under 40mph. I was thinking a softer srping or a progressive srping might help the slow speed driving without giving much up at higher speeds.

I called Eibach and found out that the stock spring rates for a n/a Crossfire is 285lbs per inch in the front and 354lbs in the rear. Mercedes claims that the SRT-6 is 50% stiffer (god help you guys). Eibach also told me (contrary to popular belief) that their springs are should actually be considered linear and not progressive. The front spring is linear and has a rate of 371 lbs. The rear are progressive with a rate of 285-371. Eibach said the progressive part of the spring is only to establish ride height and that at ride height it is 371 linear. The Eibach springs for the SLK/Crossfire are not made here but are engineered and made in Germany

I then called B&G which also told me that their springs are linear and made in Holland
and that pretty much anyone who makes springs for Mercedes makes them linear. He is emailing Holland and will be sending me the spring rates they use for the Crossfire/SLK. One thing that interested me is that he said B&G does not have a racing backgroung and sells springs mostly to people who are not looking for a stiffer ride, but are looking for a comfotable ride.

H&R wasn't very helpful as they will not let anyone know what their spring rates are. I tried to explain that I was trying trying to make a more informed decision based on facts.

My call to Intrax was very informative. I spoke to Scott there and while he didn't know the spring rate of their shocks, he said he would email the HQ in Gemany and get back to me with it. One thing he mentioned is that in Europe their roads are smoother and they have toughter restictions on the weight of vehicles that can travel their roads. the result is that MB tends to use very stiff springs and softer shocks. According to Scott to get the best ride in the US we should have softer springs and firmer shocks. I have built a few street rods and found this to be true. I got great results by using fairly soft springs with very firm shocks like Bilstein. Intrax mentioned that we should consider softer springs for our cars as long as we used after market shocks such as Koni, bislstein or KYB's. He said he might be able to get these made for us if there was interest from the SLK/Crossfire community. they all said that they have to design their springs to work with the OEM shocks.

Voughtland didn't answer the phone. That is about all the suppliers I could find that make springs for our cars.

Knowing the spring rates should be good information for anyone shopping for springs.

 

LantanaTX...I am interested in shocks....so I am watching you research...I want a stiffer shock, my springs are just fine for what I am doing, but I especially want a stiffer front shock...keep up the good work...

 

You may want to try just the KYB's in the front at first. I drove this way for a couple of days before doing the rear. You will like them in the front. The rear is what I am trying to dial in.

 

So, I mentioned this in your KYB thread and no one responded about it. What about SRT6 shocks on the NA cars? Are they more stiffly valved? Are they a better deal than the KYBs?

 

Since the SRT-6 has much stiffer springs, I would think the SRT shocks would be stiffer to control the stiffer spring. I personally would go with KYB. The KYB's seemed a little stiff at low speeds for the first couple of days but now seem to be settling down. I am really liking the KYB's now, especially when I see pot holes in front of me. Now I aim for them and am amazed that I barely feel them! The KYB's are mono tube design that is supposed to be more consistant on bumpy roads since they don't foam the oil like twin tube shocks do. I have been told that our Sachs shocks are twin tube.

 

I hAve been checking oem pn for the springs,

fr SRT6 COUPE 1 P/N
FR SRT6 VERT DIFFERENT
NA ARE THE SAME
THEY DO USE DIFFERENT ISOLATOR SPACERS

REAR SPRINGS ALL SAME P/N DIFFERENT SPACERS

FRONT SHOCKS
4 DIFFERENT P/N
REAR SHOCKS
4 DIFFERENT P/N

SO IF THIS IS TRUE, AFTERMARKET SHOCK MFG"S ARE USING THE SAME SHOCKS FOR ALL. DO NOT KNOW HOW THAT EFFECTS HANDLING ETC. i JUST PUT 4 BILSTIENS ON MINE. SOME SELLERS OFFER ONLY FRONTS FOR SRT, AND SOME SELL THE SHOCKS AND LIST THEM TO FIT ALL XF"S. iF I HAD RESEARCHED THIS MORE, I MAY HAVE PUT NEW OEM SRT P/N O N INSTEAD OF AFTERMARKET. ANY COMMENTS

 

I have K&W Variant 2's and the spring rates are 640 in the front and 480 in the rear. What really got my attention was the size of the shock shafts. HUGE! They're not the best choice for the wife and kids. Real manly parts!

Les