Improving R172 350 Handling vs CLK55, BMW & Porsche - Mercedes Benz SLK Forum

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#1 Old 05-10-2012
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Improving R172 350 Handling vs CLK55, BMW & Porsche

After owning several BMW 3 Series, I moved to Benz for a 1999 CLK430 and then to a 2001 CLK55 and have never looked back (but do miss some of the BMW handling characteristics). But with 150K reliable miles on my CLK55 I am starting to think about what is next.

If it weren't for lack of durability I would probably go to a 911 or Cayman. I don't like the looks of Z4, but could consider a 3 series coupe I guess.

But I prefer the build, design and durability approach of Benz. So I am thinking of a R172 SLK350 or SLK55. I was happy with power of the CLK430, so I think the SLK350 would be enough for me, but then I liked the handling and transmission shifting in the CLK55 better than the CLK430.

I have driven the R172 SLK350 and was happy except for the cornering which seems like a step down from my CLK55 and even that falls short short of Porsche and BMW to me. I am happiest with stock appearance, but would consider handling mods to get BMW or Porsche like handling in a R172 SLK350.

Any thoughts or suggestions would be appreciated.
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#2 Old 05-10-2012
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The R172 chassis is not likely to be as torsionally stiff as a Cayman or a 911 (not the targa) or any other hard-roofed car, e.g. BMW 3 series or CLK. So getting a 172 to corner like they do ain't gonna happen. That said, I'm sure it's possible to lower and stiffen the suspension to sharpen things up. Though essentially the SLK and Porsche (Cayman and 911) are designed to different philosophies. The Cayman is especially well known for great handling (though I've not driven one myself).

The SLK (even the R172 ).. is a very nice car that has a lot of positives. Razor sharp handling is not it's strong point, but the roadholding is actually very good even with standard suspension.
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#3 Old 05-10-2012
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You might want to try one that has the dynamic handling package and see if that's more to your liking.


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#4 Old 05-10-2012
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#5 Old 05-10-2012
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US Handling Options

In looking at the build your own at Benz USA I didn't notice a Dynamic Handling option. According to the press the Sport suspension is standard in the US as are Adaptive Dampeners. Also standard apparently is use of inside rear brakes to aid cornering. The only US handling option for the 350 appears to be 18" AMG wheels. Am I missing something?

From the AMG site, the R172 SLK AMG 55 does appear to have a different "AMG Speedshift" version of the transmission and a a sport handling mode (same as Dynamic Handling?). The steering rack appears may be different but this presumably just accelerates the response to the steering wheel as opposed to actually changing handling (although the US 350 is also variable ratio via the gear teeth). AMG Direct Steer uses brakes to help with cornering; but this seems to be standard in the 350. Then there is both the "AMG Suspension and the AMG Suspension with Performance Package."

So far my research has indentified these as AMG suspension modifications, all apparently in the base AMG:

"The AMG sports suspension, specifically tuned for high performance, comprises independent suspension struts with stiffer spring/damper tuning. In combination with all-round stabilisers with a larger diameter, more rigid torque strut bearings on the front axle as well as a more negative camber on the rear axle. Forged aluminium hub carriers reduce the unsprung masses, which benefits both the road feel and response of the spring assemblies."

With these further modifications in the Performance Package:

"The new AMG Handling package available for the first time as an optional extra enhances the vehicle’s sportiness even further. In technical terms, it comprises an AMG Performance suspension with approximately 30 percent stiffer tuning, an AMG rear axle differential lock with setup tuned specifically to the vehicle, and also composite brake discs on the front axle. In the interior, the AMG Handling package differs with the addition of a three-spoke AMG Performance steering wheel finished in nappa leather with Alcantara® inserts in the grip areas."

So it appears that a number of AMG parts could be used to modify handling of a 350. The larger stabilizer bars might be the best place to start. Wonder if they are bolt-ons? Limited slip would be of less use with the 350 engine given ESP. Aluminum hubs and stiffer strut bearings would probably be useful with a move to stiffer springs and struts. But I would assume 350 handling benefits from lower engine and transmission weight relative to the 55 which may account for much of the need for stiffer dampening and spring rates.

Last edited by CLK55; 05-11-2012 at 06:02 PM.
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#6 Old 05-11-2012
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GeeJay, thanks for the comments.

In terms of personal preferences, I think a balance more toward oversteer and minimal body roll are most important to me. I think Benz are plenty rigid platforms. My hobby car is certainly much less rigid than an SLK yet I have been able to tune the suspension to my liking.

I would like to avoid lowering an SLK given those bumper chins, speed bumps and roads I find myself on, though I understand the benefits and have experimented with lowering in other cars. But I could live with the 10mm for the US standard Sport suspension.

Sound like I might be able to use AMG parts to move in the direction I would like, with stronger stabilizers bars, sportier shock dampening and perhaps stiffer springs. If I ended up with AMG like handling in a 350 I would be happy. But I think even my beloved CLK55 (reviewed in the press as having "brutish" suspension) leans too much toward understeer (but has appropriate spring and dampening rates for my taste).

It looks like the curb weights of the AMG 55 versus 350 differ by about 140 pounds. Assuming the aluminum hubs are offset by the LSD, perhaps I could assume 100% of this weight is in the front. Or maybe there are some front/rear weight distribution stats somewhere I could use to confirm this.

This data would help evaluate AMG parts like springs and stabilizer bars for use on a 350, but since the AMG is heavier in front, just adding these parts would increase understeer (although the suspension would be much firmer).

Perhaps AMG springs should only be used in the rear or only the rear stabilizer bar should be changed to shift the balance toward oversteer. Understanding the bar diameters for the 350 versus the AMG would help. I will see if I can find these.
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#7 Old 05-11-2012
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#8 Old 05-14-2012
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Originally Posted by CLK55 View Post
I have driven the R172 SLK350 and was happy except for the cornering which seems like a step down from my CLK55 and even that falls short short of Porsche and BMW to me. I am happiest with stock appearance, but would consider handling mods to get BMW or Porsche like handling in a R172 SLK350.

Any thoughts or suggestions would be appreciated.
Handling mods for the R172 are limited and retrofitting AMG parts are expensive and may not achieve your handling goals. I guess my suggestion would be to get the SLK55 or the Porsche/BMW instead of getting a SLK350 and spending money to make it handle like another car. I believe KW offers V1 and V3 coilovers for the R172 SLK350.


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#9 Old 05-14-2012
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R172 Handling

James,

Thanks for the advice. The SLK55 is certainly an option to consider (and perhaps the best, since it has gas mileage ratings that are close to the 350 -- makes me wonder why I object to carrying around extra cylinders that don't operate much except during acceleration), although I was thinking that I could probably achieve what I want retrofitting the stabilizer bars and springs from a 55 to the 350 if I made an adjustment for the weight bias difference either in spring selection with slightly stiffer rear springs than front versus the stock 55 set up or keeping the front 350 bar with the 55 in the rear. I don't think I want to go with aftermarket coilovers, that is more in the racing and track vein than I would like to go. I would do the work one step at a time until I was happy and keep the old parts if I didn't like the change, I could always go back and then sell what I didn't want in the aftermarket when I was finished. I could do the work myself and would probably start with a move to the 55 rear stabilizer bar. Then front bar, followed by springs. There would be some savings over time avoiding the cost of those AMG rotors (Ceramic?) every few years.

But perhaps I should give more consideration to a Cayman or 3 Series coupe, though I am reluctant to give up the design quality and long term durability I have come to appreciate in Mercedes. Porsche engines need major work at 80K miles. I would consider a C Coupe or SL, but I end up with the same problem of having to go with much more engine than I need or want, just to get the best handing bits. 300 normally aspirated horsepower without understeer is fine with me (yes I know they design in the understeer for safety reasons). Even in BMW it is getting difficult to avoid turbos, and the M's often have much more engine than I would want. Ugh. Perhaps a G37 or S2000 should be on the list to look at. Meanwhile, I can continue to drive my 2001 CLK55 AMG. I guess it might go another 70-100K miles.
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#10 Old 05-14-2012
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I'd personally go and drive a '55 - I think for the changes you are proposing, you'll find it's cheaper just to go with the '55 from the start? Prices stateside are pretty amazing on the AMG to start with...



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