Improving ride quality and handling of a C350 CDI sport

[6cyl]

I've had numerous cars and driven many more, from track biased to luxo barges.

I find my C350 CDI saloon Sport quite harsh in terms of comfort, but without the handling benefits. I reckon the springs rates are too high and the dampers don't seem to react to road irregularities well enough. Too much stiction ? If it was my motorbike, I'd use softer springs, lower the compression and increase the rebound to slow down the up stroke.

To put some perspective on this, I rate the ride like so :

1. MB S350 (2011) Air suspension 18"
2. Alpina B3S (2011) 19"
3. BMW M3 (2003) Ohlins 19", polybushed
4. BMW 530i M Sport (2008) 19"
5. VW Golf GTI ED30 (2007) 18"
6. BMW M3 (2005) AP Coilovers 18"
7. BMW 530D SE (2005) 17"
8. MB C350CDI (2010) 17"
9. BMW X3 (2007) M Sport 18"
10. Audi A4 S Line (2005-2009) 18"
11. Audi S3 (2002) 17"
12. VW Golf GTI (1990) 15" on slicks, Koni track biased suspension, rose jointed, camber plates

What do you guys think ?

 

[6cyl]

No one with any comments or suggestions ?

 

[MancMike]

I don't know, you don't seem to have really asked anything, you seem to have it pretty much sussed out yourself to be honest.

If it helps, I rate my C280 about the same. Unnecessarily harsh considering it hardly handles like a sports car. My previous car was an RX8 which has beautiful handling, so I just put it down to not yet being used to the difference, but it certainly doesn't iron out the bumps, or take corners like I'd expect, nor with a trade off of one or the other. It seems to do neither very well.

 

[6cyl]

I know how it handles and reacts to the road and my inputs. I believe I have a reasonable idea on what needs to be done to improve it, the bit I'm looking for is which combination of dampers and springs and geo setting work well and to elicit other people's experiences so that I don't have to get the car on a suspension test rig and go full bespoke.

I drove a E250 CDI Sport (2013) on similar 17" wheels with Conti SC5 tyres (almost the same to mine) and it was a much better balanced car, still didn't handle that well, but at least it was comfortable.

Thanks for taking the time to reply.

 

[st13phil]

If it was my motorbike, I'd use softer springs, lower the compression and increase the rebound to slow down the up stroke.

What do you guys think ?

I think you have identified both the problem and the solution. Suspension tuning is pretty similar whether there are two or four wheels involved. IME, many "sport" suspension setups on cars are over sprung and under damped - because the average journo-twerp tells joe public that they need a hard ride to be "sporty"

 

[6cyl]

I think you have identified both the problem and the solution. Suspension tuning is pretty similar whether there are two or four wheels involved. IME, many "sport" suspension setups on cars are over sprung and under damped - because the average journo-twerp tells joe public that they need a hard ride to be "sporty"

Yes. It appears the public seems to go along with it. I like compliant suspension, that allows the tyres to do their job properly on the public road, not chase a second or two on the ring, but what the manufacturer's have given us is the worst of both worlds :fail
It isn't comfortable and doesn't handle well. This is amply illustrated by the E46 M3 on Ohlin's coilovers with 19" wheels, which is so much more comfortable, deals with the potholes, odd ridges and general poor state of our roads and still handle brilliantly. Same applies to the Alpinas in general.

Compare that to an equivalent 330i with M Sport suspension and 19" wheels, the difference is staggering. Some may think I'm off on a tangent, talking about BMWs, but the Audi S Line and MB C350 Sport is cut from the same cloth. Over sprung and underdamped and modeled on a totally bogus representation of a "sporty" drive. </RANT OFF>

 

[henley]

Suspension behaviour on many of the "sports" versions of Mercedes models, in my opinion have become their achilles heel.
Many customers are dissatisfied, dealers and sales departments know about it and are ignoring feedback. Why hasn't the UK dealers fed back to Mercedes design and marketing customers reactions. If they have, why are Mercedes struggling with this issue, or are the newer later "sport" models now sorted on this issue.

 

[rorf]

Biggest problem is the ridiculous 18, 19 inch wheels with low profile tyres - the old 124s with 15 inch rims drove like a dream. And I do not believe they handle any better. Many years ago I had a 2 litre Alfa on 14 inch rims with 185R x 14 tyres and it could probably out preform many sports cars today on the twisties

Tyre companies taking us to the cleaners considering how much less rubber they use on a low profile.

 

[bolide]

Biggest problem is the ridiculous 18, 19 inch wheels with low profile tyres - the old 124s with 15 inch rims drove like a dream. And I do not believe they handle any better.

I agree completely

It seems that only Alpina can take a car and improve the ride and handling whilst fitting lower-profile tyres

Unsprung weight has a lot to do with this. Big, heavy wheels and low-profile with stiff sidewalls make the job of the suspension very difficult

Nick Froome

 

[HB]

Stick some eibachs in it with koni sport dampers. It will be a magic carpet

 

[Lit91]

Stick some eibachs in it with koni sport dampers. It will be a magic carpet

Second that, had eibach springs on my previous car, best springs IMO!

 

[Deleted member 65149]

Suspension behaviour on many of the "sports" versions of Mercedes models, in my opinion have become their achilles heel.
Many customers are dissatisfied, dealers and sales departments know about it and are ignoring feedback. Why hasn't the UK dealers fed back to Mercedes design and marketing customers reactions. If they have, why are Mercedes struggling with this issue, or are the newer later "sport" models now sorted on this issue.

The harshness of the ride is subjective of course, but despite far too rapidly approaching my 70s, I think the ride on my 2012 C350 CGi Sport saloon is excellent in standard mode. I suppose it could be the heavier lump of a diesel engine (extra 90kg) that makes matters worse in that variant, but I suspect it's more to do with some of the "2000 changes" made from 2011. Even when in "Sport" mode with the Dynamic Handling Package in operation, the ride is far from harsh on the 18" wheels. I'm delighted with the ride quality and handling.

 

[6cyl]

Biggest problem is the ridiculous 18, 19 inch wheels with low profile tyres - the old 124s with 15 inch rims drove like a dream. And I do not believe they handle any better. Many years ago I had a 2 litre Alfa on 14 inch rims with 185R x 14 tyres and it could probably out preform many sports cars today on the twisties

Tyre companies taking us to the cleaners considering how much less rubber they use on a low profile.

If the suspension is designed correctly, the wheel size and lower profile can be compensated for. Take a look at the cars I've listed - the most uncomfortable car is on 15" wheels and 195/50/15 tyres. The most comfortable is on 18" and 19" wheels and correspondingly low profile tyres.

Jaguars, Mercedes (S class) are often on 18", 19" wheels and ride very nicely.

My 2010 C350 rides like it has over hard springs and sticky dampers. I think it is a combination of pandering to those who think that it is what we want from a sporty setup (marketing) and use of budget components.

Eibach springs and Koni Sports dampers ? I would hazard a guess that the spring rate is higher (not what I think the car needs). The dampers are the ones I had on my mk2 Golf all those years ago and it asn't comfortable.

I'd want to try it for myself first to see if it met my objectives. Any one have that setup on a 2010 W204? Preferably C350CDI.

An educated stab in the dark would be Koni FSD + custom linear springs with 10% less spring rate than the standard MB sport suspension and standard height. Bilstein B6 dampers would be another choice as they worked very well on a S3 I had. I'll see how much it costs to get the existing suspension on to a dyno and go from there so I can make a more informed decision.

 

[6cyl]

The harshness of the ride is subjective of course, but despite far too rapidly approaching my 70s, I think the ride on my 2012 C350 CGi Sport saloon is excellent in standard mode. I suppose it could be the heavier lump of a diesel engine (extra 90kg) that makes matters worse in that variant, but I suspect it's more to do with some of the "2000 changes" made from 2011. Even when in "Sport" mode with the Dynamic Handling Package in operation, the ride is far from harsh on the 18" wheels. I'm delighted with the ride quality and handling.

I've driven a facelift W204 C250CDI, it was a little more composed, but still harsh. Had standard sports suspension, no adjustments.

 

[Pitts Pilot]

The problem you have, as I understand it, is that you are virtually guessing as to what replacement suspension setup will work - notwithstanding the recommendations folk have made here, but unless they are for the same vehicle with the same wheel size, then by definition they can only be 'right' to a certain extent.

The second thing I have noticed is that you need to consider 'high speed' and 'low speed' damping as two separate things.

At the risk of stating the obvious, the damping resists the natural tendency of the spring to oscillate. Too soft and the spring acts like a po-go stick, being relatively unrestrained, and bouncing 2 or 3 times before it reaches its resting position; too firm and the damping piston does not have a chance to move up or down enough before the next bump so it 'pumps' down the barrel giving less and less travel.


The situation is further complicated by the fact that the compression stroke of the damper may be a different rate then the unloading stoke, so you have two parameters to control!


For example, my Volvo XC60 has a harsh ride around town yet lacks precision and wallows at speed on motorways. So ideally it needs softer low speed damping (towns), ideally on the compression stoke as the wheel comes out of a pothole and is forced up, and firmer high speed damping (motorways), where both compression and rebound movements need firming up.

So where does this leave you? Well when I raced bikes I would visit a suspension expect who would change the damping by altering the number or holes the damper oil had to flow through as it moves up and down. This worked well for motorcycle front forks, but the rear damper was usually just replaced with something more appropriate.
The difference transformed the bike's handing.


Therefore, IMO you need to visit a suspension expert and explain what you what. They will test drive your car and make an assessment of the high and low speed damping themselves with a view to installing something more suitable to your particular requirements.

Racing team outfits usually have the experience to do this, providing you explain it’s for a road car!

The danger is something folk have already highlighted – you get given very firm suspension because it’s thought to be ‘sporty’. The dilemma with this is that on a race track were most of the suspension’s work IS done at high speed – you are racing flat out after all – what you and I would consider to be overly firm suspension is just what you need! So it’s not a perfect solution.

My alternative suggestion is that you drive different suspension setups for your car, say the “Elegance” version car rather than the Sport, and if you prefer that then specifying new suspension would be easy. Other than that you could use Audi suspension (or BMW, etc etc) but you would need to a) know the dimensions of the shock absorbers and their end fittings, and take the setup from similarly sized/weight vehicles.


Frankly the latter will be difficult, so in conclusion:
I’d seek expert help from a suspension tuner, who might even be willing to let you ‘try before you buy’. I don’t envy your mission 

Cheers,
Robert

 

[nb_racing]

I think Pitts Pilot has nailed it on the head.
In addition, tyre pressures are critical. I'd play with those first.

 

[6cyl]

Robert - I have modified suspension my cars in the 80s then latterly my bikes. My last bike had standard, Nitron then Ohlins dampers. The latter had low and high speed compression and single rebound adjustment on the rear. Both front and rear were sprung to suit me, Ohlins cartridges at the front. Steve Jordan set it up for me.

Thats why I'd rather not just chuck on Eibach, Penske or whatever on the car, recipe for dissatisfaction and spending too much money.

I need to find someone that either knows the car well and understands what I want or knows how to work it all out on a suspension dyno, measuring the spring rates and damper characteristics combined with corner weighting of the car.

A bit of suspension info for the people reading this (not you Robert, as you're likely to know this already)
High and low speed refers to the shaft velocity of the shock absorber. Small high frequency undulations and big, slow bumps. It is not necessarily related to the speed of the vehicle.

 

[Pitts Pilot]

I'd rather not just chuck on Eibach, Penske or whatever on the car, recipe for dissatisfaction and spending too much money.

I need to find someone that either knows the car well and understands what I want or knows how to work it all out on a suspension dyno, measuring the spring rates and damper characteristics combined with corner weighting of the car.

Agreed entirely! Sounds like we have both had experience of setting up suspension? Hardly surprising the serious race teams (2 & 4 wheels) have a guy who just does suspension....!

Anyway, this is not helping you


When I had bikes their was a guy in Southport who would take your bike, re-spring, blue print, and change the oil in the front forks and as a result they were completely transformed! You need a car version of this guy!!

Hence my suggestion of a suspension 'tuner'. Problem is I don't know one :-(
That's not to say they don't exist.

I'm reminded of specialists like Eurocharged and MSL who do bespoke exhausts. You tell them how loud you want it; what kind of sound etc, and they put one together just for you.

Surely there must be the equivalent for suspension?

Where do the Formula Ford teams get their suspension advice from, for instance?


I think your best bet is going to be with the racing sector, and I don't mean car parts and accessory shops that sell "Tuning parts". I agree that would be a total waste of time and effort.

I'm just throwing out ideas in the hope it might give you an idea. But in truth, I would have to start looking on the internet if I were in your position.


Have a read of this, particularly the section on "Corner weighting". Northampton Motorsport - Suspension Set-up

They seem to know what they are talking about. Just an example

Best wishes,
Robert

 

[grober]

Part of the problem is that in that model Mercedes persited with using their "adaptive damping shock absorbers" These are the poor man's adjustable suspension which uses shocker adjustment mediated by self contained inertially weighted control valves. While this can "adjust" the damping it simply doesn't adjust quickly enough IMHO. This is particularly apparent with what I would term high frequency vibration as opposed to major suspension movement leading to harshness . The optional "Dynamic handling package" uses electronically valved dampers together intertial sensors and a control ECU is a much more sophisticated system. A carefull match of non adjustable springs and dampers may actually yield a superior result to the standard adaptive damping setup.

 

[6cyl]

Robert - I can think of half a dozen motorbike suspension gurus, I know of none in the 4 wheeled world, but they must exist. I'm sure the principles are the same, but the physics of suspension geometry for 2 and 4 wheels is going to be different in practice.

Graeme - I wasn't aware the pre-facelift W204 dampers were self adaptive, may be mine aren't working properly?

Knighterrant "Even when in "Sport" mode with the Dynamic Handling Package in operation, the ride is far from harsh on the 18" wheels. I'm delighted with the ride quality and handling. "

MB must have sorted the suspension out on the facelift w204 with dynamic handling, which ties in nicely to Graeme's comments. This is not unprecedented in the car world, the facelift (LCI) BMW E60 suspension is much improved over the original E60 2004-2007 versions that worked a lot better with run flat and lower profile tyres.

To me, the the primary ride on my car, determined by low speed damping isn't right, the compression is set too high, the springs are not given that much chance to compress or there is too much stiction, so it takes more force to start reacting to the bump. I feel the rebound can be increased, so that the up stroke is slowed down a touch. My guess would be either that the dampers are partially faulty or just plain cheap.

The issue I'm experiencing is way beyond fiddling with the tyre pressures though, that is more likely to affect the high frequency response. My plan of action is to see if I can find someone that can help me analyse the car's suspension.

As an aside, I've had the car for 18 months or so, hasn't got any worse, so I must have been wearing rose tinted specs whilst test driving it. I've also driven similar cars, C250, newer and older and they seem to be simlarly afflicted.

I'll report back here once I get some results ... or change the car.