[VWoT] How's my Math?

["bokchoi" <bokchoi@xxxxxxxx>]

Check this out and let me know if any of these #'s make sense.

I decide to calculate spring rates in order to figure out why i've been
blowing my rear shocks.  Here are my results:

K = ((W^4)*G) / (8*N*(D^3))

where
K = spring stiffness/rate (lb/in)
W = Diameter of the coil wire (in)
G = 12,000,000 (shear modulus of steel)
N = # of active coils (free coils + 1/2)
D = Diameter of the coil (in)

OEM Mk3 Jetta 2.0L front spring
W = 12mm = 0.472in
N = 4.5
D = 5.0in

Therefore K = 132 lb/in

OEM Mk3 Jetta 2.0L rear spring
W = 10mm = 0.394in
N = 6.5
D = 100mm = 3.93in

Therefore K = 92 lb/in

H&R Race Mk2 Jetta front spring
W = 13mm = 0.5118in
N = 2.5
D = 128mm = 5.0in

Therefore K = 330 lb/in

H&R Race Mk2 Jetta rear spring
W = 13mm = 0.5118in
N = 3.5
D = 102mm = 4.01in

Therefore K = 460 lb/in !!!!!!

This could be the reason that the fronts feel so good but the rears keep
blowing up.

So if i decide to play with the OEM rear springs:

OEM Mk3 Jetta rear spring (-1 coil)
N = 5.5
K = 108 lb/in

OEM Mk3 Jetta rear spring (-2 coils)
N = 4.5
K = 132 lb/in

OEM Mk3 Jetta rear spring (-3 coils...that's just going too far)
N = 3.5
K = 170 lb/in

I believe Shine Racing runs ~130-150 lb/in for the rear with their
kits...although they also like to remove the front sway bar and they hate
lowering.

-- 
d8ve
94 Golf GL - 98 Jetta GT - 01 CBR600F4i



-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
This is an automated post from the list@vwot.org mailing list.  To stop
receiving this list, send an email to "majordomo@lunaticfringe.org" with
the words "unsubscribe vwot" in the message body.  For more about the
VolksWagens Of Toronto group, visit http://www.vwot.org/community
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-