Is there a way to tell if a shock/spring unit is overdamped/underdamped just looking at data? Let's say, max valving force, spring rate and mass.

he reason I ask is that I installed Bilstein Sport shocks + Eibach Prokit Springs, and the ride has been really very rough even though the springs are of pretty conservative rate- 220F/180R (rear is progressive)

When I called Bilstein to find out the specs on the dampers, they wouldn't send me the graphs, but they did share the peak damping force values. These values are at .524 m/s:

Front rebound/bump: 5505/1865 N
Rear rebound/bump: 2030/1140 N

Looking at the graphs of the dyno's of the other ots shocks, these values seem very high, particularly the front rebound.

Could it be that the system is very overdamped? How do you tell?


Modified by vinuneuro at 5:33 PM 12/18/2007

 

I guess this is what I was asking about in the topic I posted a little while ago. Because of a harsh ride I'm switching to a softer spring setup while keeping my skunk2 pro-s shocks. I too wonder if I'll still have a harsh ride because of being 'overdamped.'

 

according to my *** dyno, bilstein sport shocks have always felt over dampned

which doesn't bother me, as i like a stiff ride

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vinuneuro &raquo;</TD></TR><TR><TD CLASS="quote">Is there a way to tell if a shock/spring unit is overdamped/underdamped just looking at data? Let's say, max valving force, spring rate and mass.

he reason I ask is that I installed Bilstein Sport shocks + Eibach Prokit Springs, and the ride has been really very rough even though the springs are of pretty conservative rate- 220F/180R (rear is progressive)

When I called Bilstein to find out the specs on the dampers, they wouldn't send me the graphs, but they did share the peak damping force values. These values are at .524 m/s:

Front rebound/bump: 5505/1865 N
Rear rebound/bump: 2030/1140 N

Looking at the graphs of the dyno's of the other ots shocks, these values seem very high, particularly the front rebound.

Could it be that the system is very overdamped? How do you tell?


Modified by vinuneuro at 5:33 PM 12/18/2007</TD></TR></TABLE>

Afraid the numbers are meaningless to me. But I can share personal experience.

2000 GSR, 400/400 rates on OTS Koni Sports (Yellows)
I can decidedly feel the difference from full soft (slightly underdamped, and how I daily it), 1/4 from soft (feels about correct), and full stiff (very very harsh ride). Since the Konis only adjust rebound, I can say that too much rebound, does result in a "harsh" ride.

It doesn't feel stiffer or anything, as the suspension still compresses the same amount for a given bump, but the car just feels significantly harsher after the bump and over pavement transitions.

Hope that helps some.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TunerN00b &raquo;</TD></TR><TR><TD CLASS="quote">

Afraid the numbers are meaningless to me. But I can share personal experience.

2000 GSR, 400/400 rates on OTS Koni Sports (Yellows)
I can decidedly feel the difference from full soft (slightly underdamped, and how I daily it), 1/4 from soft (feels about correct), and full stiff (very very harsh ride). Since the Konis only adjust rebound, I can say that too much rebound, does result in a "harsh" ride.

It doesn't feel stiffer or anything, as the suspension still compresses the same amount for a given bump, but the car just feels significantly harsher after the bump and over pavement transitions.

Hope that helps some.</TD></TR></TABLE>

Would higher rate springs help my situation then?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by vinuneuro &raquo;</TD></TR><TR><TD CLASS="quote">

Would higher rate springs help my situation then?</TD></TR></TABLE>

Wouldn't that just be trading harsh for stiff (assuming you bought springs matched to your dampers)?

 

The springs are not matched by any means. They're of pretty low rate (220/180) for a car that weighs nearly 3,000lbs.

 

While 5505 newtons is a lot of force, it is also occurring at a pretty high piston speed. One data point isn't really enough to tell you if that corner is over/underdamped, but judging by your spring rates, that is the only reason I can think of for an overly harsh ride, aside from other more obvious factors like over-inflated tires or spring "stoppers" between the coils bumping up the rates, or something bottoming out.

 

Al, everything is installed properly, and the shocks are new and not defective.

I had a conversation with a Bilstein engineer today. While he didn't have the graphs for these shocks since they were developed in Germany, he was able to give me another value for a lower piston speed. At .26m/s front 4650/1575, rear 1585/785. While I realize the numbers are not the end all, it is helpful esp without a graph.

Another thing he told me is that from testing they've found that Eibach springs are often softer than even oem rates. He told me to try another spring mnfr like Neuspeed to increase rates or get custom rate springs because the current setup is indeed overdamped.

He also indicated is that these shocks are valved pretty aggressively and would be able to damp pretty high rates (higher than 600#).


Modified by vinuneuro at 3:26 PM 12/19/2007

 

Those seem like extremely high rates for the springs you have. To put them in context, I looked up the damping forces for a racing Tein RA for a DC2 Integra. At 0.25 m/sec (a high shaft velocity of 10 in./s more about hitting bumps than handling). The car is 2650 lbs without driver and 62% front weight. The front RA dampers at 0.25 m/sec have a min/max force of 3100-3800 Newtons in rebound and 1000-1100 Newtons in bump. The intended spring rate for those dampers is 12 to 16 kg/mm or 670 to 900 lbs/in. The rear Tein RA's 2100-2400 Newtons in rebound and 730-830 in bump and designed for 450-670 lb/in springs. You actually need corner weights and motion ratios to start calculating what springs you need and what damper settings to go with them,since one usually starts with setting dampers to a % of critical damping. But those Tein RA rates give you a ballpark idea on a similar car of what damper forces match what springs.

Either get much stiffer springs to match the dampers you have or change dampers.