Re: [VWoT] How's my Math?

[Robert Emrich <rob.emrich@xxxxxxxxxx>]

Assuming the formula is correct, the math is fine.

This may be completely useless, but the rear springs typically have a  
lower spring rate than the front springs due to lack of weight back  
there (which I assume you know).

The front spring rate increased 198 lb/in or 150%, so I am assuming  
that for the rears to feel similar, an increase of the same percentage  
should occur, this 150% increase is 138 lb/in which would result in an  
approximate 230 lb/in effective spring rate for the rear spring.

I'm sure you installed everything properly, but when you compare the  
high spring rates (OEM F, H&R R) there is a 248% increase and the low  
rates (OEM R, H&R F) it is an increase of 259%.  This looks to be a  
better match, than the current set up, while still allowing for  
increased rotation in the rear.

Of course, I know nothing of Automotive suspension design and logic,  
I'm just throwing in my $0.02

Rob

On 16-Nov-04, at 23:39, bokchoi wrote:

> 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
> -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- 
> =-=-

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
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
-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-