Re: [VWoT] How's my Math?

[Dumitru Hociung <fivemileshigh@xxxxxxxxx>]

One thing I can tell you for sure about MK2 H&R race springs is that
the spring rates are 400 lbs/in linear front, 230-260 lbs/in
progressive rear, and this is straight from H&R by phone. Also
according to Koni, their Mk2 Yellows are the strongest off-the-shelf
shocks you can buy for the Mk2 (don't know how that applies to the
Mk3).

By removing the front sway, you have more front lean (a bit) but you
also get more grip (oddly enough). This helps with powering out of a
corner because for the same amount of "G"'s you retain more weight on
the inside tire. This all happens assuming the rear bar is kept. I
tried it on the rocco, it is a very noticeable difference, the front
end has more grip, the rear does not, which means less understeer. You
also lose 10-15 lbs off the car which is always a bonus.

Great mod if you know how to drive, not so great for amateur winter drivers.

SRS does have a point about excessive lowering for street cars with
McPherson suspensions.

this all is afaik, ymmv, etc ad nauseaum, feel free to correct me.

D



On Tue, 16 Nov 2004 23:39:45 -0500 (EST), bokchoi <bokchoi@vwot.org> 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
> 
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