Damping Constants: Sports VS HD

[yesterdaylight]

For the engineering minded people here... I gave Bilstein a call because I was interested in the differences between their sports and HD stocks. I am not sure if these numbers are application specific - I let them know it was for a 2002.

They gave me a number in Newtons at a specific velocity (.52m/s)

Below are the numbers they supplied to me directly:

FRONT

Sports-

Compression: 2150N

Rebound: 1110N

HD-

Compression:1660N

Rebound: 780N

REAR

Sports-

Compression: 2351N

Rebound: 664N

HD-

Compression: 1215N

Rebound: 575N

With a little basic math considering this equation:

F=CV where F is force, C is a damping constant, and V is velocity

Going on the assumption that these shocks dampen in a linear manner, which I'd suspect they do (does anyone make progressive rate dampers?)

so C = F/V

A table of damping constants follows in N*(S/M):

FRONT

Sports-

Compression: 4134.6

Rebound: 2134.6

HD-

Compression:3192.3

Rebound: 1500

REAR

Sports-

Compression: 4521.2

Rebound: 1276.9

HD-

Compression: 2336.5

Rebound: 1105.8

Hope some people will find this helpful!

-Ian

[allbim]

Thanks for the interesting data. I'm surprised there is so much dampening on the compression stroke compared to rebound.

W. b>

[yesterdaylight]

Not a problem, hopefully this helps people working on matching dampers and springs. Also, if you think about it - the compression damping must be quite a bit higher than rebound because you are damping the entire weight of the car (sprung weight) in compression, and only damping the unsprung weight in rebound. Or if you think about it in the reverse, with the dampers actually acting with a force, they must have less dampening on the upstroke because they are pushing the entire weight of the car up, while they must have much higher dampening constant while pulling sprung weight weight down.

See: http://en.wikipedia.org/wiki/Damping_ratio for a little more info - it's mostly correct...

I did a few calculations of my own assuming IE Stage II's and Billy sports - discovered the system seemed quite a bit overdamped... but I may have been missing something - Like a rule of thumb for automotive damping ratio or something.

-Ian