We had a thread recently on spring rates. How about shock rates? Here's what I found out, with some research at Bilstein:

964 to '90 (Bilstein HD)
...Front 332/104
...Rear 274/122

964 to '94 (Bilstein HD)
...Front 332/104
...Rear 277/124

964 Carrera RS
...Front 259/84
...Rear 415/237

964 Cup
...Front 220/67
...Rear 379/172

964 RSR (3.8L)
...Front 237/96
...Rear 402/216

The values are read as rebound over compression, ie, the first number is the rebound value with the second being the compression value.

I don't have the valving on the stock Boge's on our 964's, however, thought this might be of interest.

 

Bill,

What physical quantity do the numbers represent? Dampers provide resistance to motion that varies as a function of velocity (the in/out velocity of the damper) so do these numbers represent force/velocity ? If so, what units?

Doug

 

Doug,

The standard values are decanewtons at a piston shaft velocity of .5 meters (500mm) per second. A decanewton equals 10 newtons equals about 2.2 lbs of force. (Reference: an excellent two part article entitled "996 Standard and Sport Suspensions Analyzed" in the April and May Pano's).

 

Bill,


Ah yes..... Decanewtons. I've never understood why people choose to use decanewtons. For this measurement I would have used kN (kilonewtons) - giving decent values like 3.79kN (379 Decanewtons)etc.

I once did some work for a French wheel manufacturer and everything was done in Decanewtons - I didn't like it then either....

I guess that the .5m/s velocity chosen for the specification must be representative.


Thanx

 

Bill, Very good info! Are those #s applicable to the 911/930 Bilstein #s also?

 

I think the Europeans choose the decanewton because it represents a kilogram of force and they think in kilograms like we think in pounds.

The 500mm per second value represents a snapshot taken during the center of the speed envelope that the shock shaft works at. The 500 mm/sec value is also around the shaft velocity one sees hitting a pothole and gives some indication how "harsh" the shock may ride in comparison to another shock when hitting a pothole. The range of the shaft speed envelope is from 0 to around 1500 mm/sec with less force required to move the shaft at slow speeds that it takes to move the shaft at higher speeds.

To quote the Panorama article Bill mentioned above:

1. Low shaft speeeds are 0 to 130 mm/sec and be a gentle undulation in the road-or the slow chassis motion one feels when turning into a corner.

2. Intermediate shaft speeds would be 140 to 500 mm/sec and would be like hitting railroad tracks.

3. 500 mm/sec and above is pothole city.

The shock designer can choose different valving that controls force of shaft motion required at different shaft speeds controlling either slow chassis motion and weight transferr the "sprung weight" or wheel motion "unsprung weight". So shocks are critical to both handling and ride. <img src="graemlins/yltype.gif" border="0" alt="[typing]" />

 

[quote]<strong>Are those #s applicable to the 911/930 Bilstein #s also?</strong><hr></blockquote>

Bill,

No, the 911/930 Bilsteins have different rates. You can contact Bilstein for the specific values, as the 911/930 values are not listed online. They can probably fax the list to you.

Today's trivia: 934 struts/shocks are valved at 200/170 in front and 220/180 rear.

 

Intersting post, Bill

Perhaps, do you know those values for stock damper, for a stock C2 and a C4 ?

Now on my C2 I have C4 dampers, and I'll have an idea of how much my c2 is stiffer than a stock one.

Thank you

 

[quote]<strong> do you know those values for stock damper, for a stock C2 and a C4 ?

</strong><hr></blockquote>

Herbie,

Sorry, I don't have the stock Boge shock values. Someone else??

 

OK, after e-mailing Bilstein for values of my VE3-5277 front struts, I conclude that they ar very close to the RS rebound/bump rates, as below:

VE3-5277 and VE3-5278

velocity .13 .26 .52

rebound 305 1715 2230
bump 95 610 845

V36-0384 and V36-0385
velocity .13 .26 .52

rebound 2115 2830 3320
bump 616 830 1040

The numbers seem to suggest that they are softer than stock - I would have expected RS dampers to be harder??

 

John,

What are the 5277/5278 struts? The 0384/0385 are the Bilstein HD's for 964's, and the Carrera RS struts are V36-0155/V36-0156.

The strut dampers need to match the springs. RS springs are progressive vs the stock springs.

 

The 5277/5278 were supplied to me with 'Gemballa' H&R springs. I am assuming, at this stage, that they are struts specially made by Bilstein for Gemballa, valved for these particular H&R progressive springs. The rebound & bump values certainly seem to be set up for progressive springs AND seem similar to RS spec struts- but these are much 'softer' numbers than the HD's.

Bilstein UK just told me that these dampers (5277/5278) are standard replacement dampers. Apparently, Bilstein no longer make the V36-0384/5.

Also, the mono tube design is allegedly better, oil stays cooler. Either way, I will report after the install on Tuesday.