[s-cars] spring constants

[Richard Tanimura]

Trevor,

I used the same calculator and the same measurement technique for all the
springs so if there are errors, I assume they are atleast pretty consistent
for all the springs. This would mean that even if the absolute values are
off, atleast the relative values are of some interest. Here is the
reference:

http://www.kaila.net/tl125/spring.html

Lets try agree on the basics. I assumed that the larger coil diameter
provide the lower spring constant. And the tighter diameters at the ends
have a higher spring constant. I used the larger diameter of the coils for
the calculation. Not the smaller diameters at the ends. So the spring rates
calculated are the initial unloaded ones. This can easily be tested by
simply changing the coil diameter keeping all else constant. You get a
harder spring.

So in answer to your question "when" the answer seems to be from git go and
then it just gets bigger :-)





-----Original Message-----
From: Trevor Frank [mailto:tfrank at symyx.com]
Sent: den 19 mars 2004 18:46
To: Richard Tanimura; s-car-list at audifans.com
Subject: RE: [s-cars] spring constants



These are all I believe progressive rate springs that are intended to be
pre-loaded, so your calcs are off. As with this type of progressive
wound spring, it is designed so that the coils will bind progressively,
meaning that the number of active coils decreases as it get's
compressed.  From looking at them there are probably at least two
different windings in these coils, so there may be a strait rate portion
after the first few bind.
I have laughed when people have quoted like 3XX# spring rate for these
spring because, sure, but when?

-----Original Message-----
From: Richard Tanimura [mailto:richard at tanimuras.com] Sent: Friday, March
19, 2004 12:11 AM
To: s-car-list at audifans.com
Subject: [s-cars] spring constants

First, I don't have an S4. My car is an S2 with a 3B motor and a B4
chassis.

I just bought a set of H&R springs for my car. I measured pretty
carefully
and ran the numbers through a calculator for spring constants. Does
anyone
have similar data for the stock or aftermarket S4 springs?

H&R, Front axel, S2:

Wire thickness: 0.54"
Winding outer diameter: 5.9"
No. of active coils: 6.5
Spring constant: 125 lb/inch

H&R, Rear axel, S2:

Wire thickness: 0.54"
Winding outer diameter: 5.9"
No. of active coils: 5.25
Spring constant: 155 lb/inch

-----------
I also have some MTM spec:d Eibach springs. I think they are for the
S4/A4.

MTM, Front axel, S4/A4?:

Wire thickness: 0.60"
Winding outer diameter: 5.47"
No. of active coils: 3.8
Spring constant: 419 lb/inch (Yowza!!)

MTM, Rear axel, S4/A4?:

Wire thickness: 0.31"
Winding outer diameter: 3.9"
No. of active coils: 8.7
Spring constant: 32.43 lb/inch (Very soft!!)

Something fishy here I think. Any ideas.

Richard
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