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Old 12-12-2001, 02:45 AM   #1
ANZAC_1915
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Default WRX US OEM vs STi/SPT sedan spring rates ... again

Here are my latest wild assed guesses:

OK, the actual FHI specs for the SPT/STi kit is:
38 N/mm F
33.4 N/mm R
(source: SOA, though they quoted N/m not N/mm).

This looks very close to the relationship between what I'd calced for front and stiffest possible for rear (lower coils bound).

That gives us for STi/SPT:
217 lbf/in F
190 lbf/in R

If you then take my prior comparisons between the springs -> 27% stiffer at front, and 107% stiffer at back (stiffest) and work backwards, then you get:

US WRX sedan:
169 lbf/in F
92 lbf/in R

Note how soft the rear is compared to the front, compare to either the rates Jamie Drummond measured for the Aussie WRX and the STI rates.

Believeable?

Glenn
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Old 12-12-2001, 12:38 PM   #2
tt_ttf
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Seems really low value for the rear spring rates (what were they thinking?) but believable given the rear end dance the rear does on throttle lift off in a corner!

Also would explain the huge improvement in lift on your car under acceleration
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Old 12-12-2001, 01:12 PM   #3
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hmmmmm

169 for the front seems really high the 110-120 #s sound better

a differance in the stock spring rates that big would create some intesting handeling

if you use the same 101% gain figure with th front you get ~106 .. which i think is closer

side note:
notice the similarities in the sti/spt spring rates vs the v.5 spring rates (very simmilar) with in ft/lbs
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Old 12-12-2001, 10:21 PM   #4
ANZAC_1915
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Quote:
if you use the same 101% gain figure with th front you get ~106 .. which i think is closer
Yeah, but you can't use that cos I didn't measure that as a difference between the two sets of front springs.

DEFINITELY there is a huge spring rate difference between the front and rear OE springs. The rear is very soft.

Glenn
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Old 12-13-2001, 04:11 AM   #5
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Very interesting... Wonder if someone might try to put a pair of the front springs on the back to compensate? (I know it will screw up the geometry, but it might be worth trying to see)
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Old 12-13-2001, 11:40 AM   #6
ANZAC_1915
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I seem to recall there are diameter differences at the top (or bottom?)

Glenn
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Old 12-13-2001, 01:52 PM   #7
tt_ttf
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Quote:
Originally posted by Kostamojen
Very interesting... Wonder if someone might try to put a pair of the front springs on the back to compensate? (I know it will screw up the geometry, but it might be worth trying to see)
There was a taper in diameter on on one of the springs (think it was rear) plus differences in the rubber. The rears had very substancial boots on the top of the springs plus there was differences in the shock perch.
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