Marcus Frost - 6/6/2011 12:07 PM

Wanted to update this thread since it generated a lot of interest.

When I first made the thread and was borderline complaining about the ride, it actually turned out both of my front shocks were blown. 30k miles, no offroading. Covered under warranty. We didn't know at first why the truck was making so much noise and being so stiff (even for a G) when going over harsher bumps but it rattled the hell out of me and my tech agreed something was up. He essentially replaced much of the front suspension including a lot of the bushings, the shocks, but not the springs. It was a big bill so we decided not to try and install Koni shocks because we were not sure at the time if that would resolve the problem. It did, but I already had the Koni shocks and decided to hold off on installing them.

Now the car was due for brakes and an A service, so I decided to use this time to do the shocks as well. I am told by my shop that the SPXs are either out of production, or going out of production according to Koni. I did not try and verify this, but those who are on the fence may want to call Koni and ask them about the availability of the SPX shocks for our W463s.

After Tom's issue I am somewhat concerned about making sure that the install goes well, thankfully I do not cut corners on these matters and have the most competent people I know doing the install. I am going to set the shocks for full soft front and rear to start with, and may turn the rear a half turn stiffer as required. If anyone has any suggestions for stock reds front stock browns rear on SPXs in regards to what stiffness to set the shocks at, I would appreciate it.

I will report back progress.

Regards,

Marcus

Razon - 6/6/2011 4:47 PM

I have the same shocks.

How do you make them harder? The only adjustment is for rebound.

ewalberg - 6/7/2011 2:29 PM

Both rebound and compression are critical to vehicle stability.

i really disagree with 512bbi that compression is only for controlling unsprung weight. it is absolutely critical to managing body roll during cornering and preventing bottoming out on larger bumps, and in general it has more effect on how smooth or rough the car feels over bumps then the spring rate or rebound.

As an example, i blew out the damper on my bike shock and i had to more than doubled the air spring pressure in the shock (in fact i maxed it out) and despite maxing out the air spring to be MUCH stiffer it was SUPER plush and soft riding compared to with the damping circuit working... but and it would still bottom out WAY too easily.

Though all the inputs matter (spring rate, rebound and compression damping) compression damping is the most important component of how the ride feels. Rebound is very important to vehicle stability for reasons that 512bbi mentions, but it has less impact on how smooth the suspension feels than compression damping. I've recently installed double adjustable shocks on my lotus. The springs are 25% stiffer all around, and the compression and rebound are both adjustable via nobs, and the compression dial makes the biggest difference on feel over bumps. But 512bbi is right, rebound does still definitely have impact on feel and control of driving. Regardless of 25% stiffer springs all around, the shocks are softer feeling over bumps. The compression circuit can be run lighter than the original springs and shocks, and rebound kept at a level which maintains stability.

One of the primary reasons why i hesitate to go with aftermarket shocks is becuase the existing shocks were (i believe it was said here) a compromise of highway and offroad driving geared towards maintaining safety in faster off-road driving... so the reason for the stiffer compression damping is to avoid bottoming out the truck and bending an axle on higher speed off road driving. To complicate matters shocks can have separate high speed (small bump) and low speed (large bump) compression damping circuits, (so just how they feel isn't always a perfect indicator of ability of a shock to resist bottoming out) but long story short is that if you don't know someone (or many people) with specific experience with those shocks, then a "softer" riding shock may be great on road and okay for slow off road driving but you could be in for some surprises when you hit bigger bumps off road at speed.

Razon - 6/7/2011 8:38 AM

The reason I asked is because I adjusted my front shocks (180deg towards hard) and I can't tell if it rides any harder.
It does feel different, but I wouldn't describe it as harder, or a harsh ride. I was actually thinking to go more and see how it feels.

I have the red front springs and yellow orange rears. From previous posts I remember the weight of the tires being important as well for proper calculation. The ones I have are about 90lbs ea, without the rim. Where do you send this info?

ewalberg - 6/8/2011 3:31 PM

We really aren't talking about the 55k's unusual suspension design... we can include it, but it's going to make things more complicated.

It's clear you basically understand the purpose of the different aspect of compression damping, rebound damping and springs, but we're going to have to agree to disagree that we have a fundamentally different understanding of how important and how critical and how primary compression damping is to suspension design and bottom out prevention. My experience, education, and understanding is that even at minimal speeds it is precisely the shocks (and not the springs) that are doing the work to keep you from bottoming your suspension. Like i said, remove your shocks and see what you get. Try driving through an intersection with water flow drops at 20mph and see what you get without compression damping. Try crawling over a simple speed bump in a mall parking lot and see what you get. You WILL be shocked.

When you slowly drive over a speed bump in most conventional cars with limited suspension travel the primary thing that keeps it from bottoming it out is the compression damping. As an example, I have an old co-worker who has an late 90's audi a4, and slowly driving over speedbumps at very low speeds you can absolutely feel the car bottom out on the back side of the bump. I don't know if it's set-up that way for generally soft ride, or if her shocks were bad, but i gauranttee you her springs were in good working order... the shocks may have been still okay and by design, but it was under-damped no matter what.

I'll bet i could bottom out virtually any g-wagen at less than 10mph on a driveway or a mall parking lot if you remove the oil damped shocks and use only springs. AMG's decision to use additional elastomers in their suspension would be nothing more than further proof that compression damping is critical becuase elastomers fundamentally have a component of damping to them which springs do not. Elastomers are capable of absorbing much more energy than springs. Conventional suspensions (of any kind) generally do not use bottom out bumpers as an continuos part of their suspension as AMG has chosen, in part becuase they're highly temperature sensitive. On the vast majority of vehicles, they suspension is basically intended NOT to hit those becuase they're usually only there as a last ditch design addition to keep you from damaging parts with a hard bottom of metal on metal, or vehicle to road.

I agree there is no free lunch, i agree things must all be balanced and there are compromises to make ride comfort and control. I'm not disputing that you need additional bumpers in AMG suspension to make it stable. These things change nothing in my argument. The bumpers are nothing more than one way of executing an increase in spring rate AND an increase in compression damping. You may need them because there is not enough space to do with conventional springs and dampers, but those bumpers are not the ideal way of getting the outcome you have. There is nothing about those elastomers in AMG design which could not be accomplished with a properly designed spring and damper system (if they had the space)... but their decision to chose that route probably was a required compromise due to limited space. It may very well be the best solution all things considered.

thinking more about this, maybe our missunderstanding is that when i say compression damping prevents bottoming out, i mean that it does so in general, but not as an absolute rule. My point is that if you didn't have compression damping on cars today you would find they are remarkably easy to bottom out in regular driving and in many cases where you think that the spring is doing the work to prevent bottom out, it's actually the shock doing it. However, becuase comfort is important the compression is not so stiff that you can never bottom out... if you hit a big enough bump hard enough you can still definitely bottom out. I have bottomed out my g-wagen on the freeway when i hit a snow bank left by a snow plow that i thought was just powder, so to your point, compression damping doesn't fundamentally prevent bottoming out, but it defintely the primary thing keeping cars from bottoming out in general driving.

Redbull Addict - 6/30/2011 11:59 PM

OK gents...it's my turn again

the last time you heard from me I installed a new Koni SPX and it was marginally better. 15K miles later I can't take it anymore. With my BFG AT's 285/65/18 E-rated at 32lbs cold, the truck feels like its bottoming out when hitting potholes or speed bumps at anything over a slow speed. It really feels like something is going to break. This past weekend I was in Death Valley with a fully loaded truck trying to fly across those nasty washboards and it felt like I was going to destroy the truck. I know the SPX are good shocks but perhaps because of the oversized and very heavy tires the original springs and SPX combination is not working for me.

My question is where do I go from here? I need this truck to ride more comfortably onroad and handle the washboards better offroad both loaded with gear and without. The current setup sucks.

Are the 2 strip red springs stock on the 463? Do I need something stiffer to handle the extra unsprung weight? based on what I read in this thread the SPX may not be the right shocks for me...so I need the Koni 90's? I rather not get Koni's after the crappy support I received.

I'm open to all suggestions. :cheers: