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Spring tolerances are +/-3mm at ride height and +/- 7lb/in rate.
At ride height, oem sti spring rates measure 217 front, 171 rear.
JDM sti pink front measure 223, at ride height.
Required specs:
Daily driver/occasional track day.
F245lb/in R223lb/in at ride height
Linear spring rates, in their operational range.
Increase spring free length, to ensure no dislodging, at full droop - non-inverted dampers extend further, than inverted. Eg front Koni inserts are 35mm longer.
Revise the bump stops for inverted and non-inverted dampers: front - account for the lower front ride height, and rear - stiffen.
Don't go too low at the front - bump travel (and spoiler lips ).
New widetrack OEM sti front ride heights compared to new:
Prodrive 05-07 sti red S05/D5/001 -18mm
WA/A2 -23mm JDM sti pink -28mm
RB320 -31mm
Consider how the revised spring rates will effect ride frequency.
Take the extra rear weight of the wagon variant into consideration.
Keep the rear ride height close to the stock sti.
As utilised on the RB320 - increased positive rake:
A, relatively, higher rear ride height moves the roll centre rearward, increasing rear roll resistance.
That, in turn, makes the front end roll more - helping turn-in response and reducing understeer, without the use of stiffer bars.
You want the smallest bars possible, on a road car, to avoid 'roll-rock'.
Roll-rock:
If the spring rate is relatively low and the bar is too stiff, a suspension movement, initially, occurring on only one side of the vehicle, will be transmitted to the other side, inducing an unsettling 'roll-rock' motion and destablizing the tyre contact patch.
The bump stop selection also helps mitigate against understeer. On undulating/uneven roads, you may find the use of a bigger rear bar unnecessary/unhelpful.
Last edited by 2pot; 23 November 2019 at 02:26 PM.
I can fully endorse the advice on the bottom of the OP's post.
So we all know exactly what is being described, I'll have a go in simple English (ish)....
Imagine the roll centres of the car floating between the wheels and a line drawn from the front to the back. Extend the lines out like a barbecued piggy style. This is the axis around which your car will roll.
Making it roll is a torque generated by centripetal force acting on your CoG and rotating the car around the roll axis. Resisting it is the springs and ARBs.
Problem. On a McPherson Strut design, the Roll centre is based on the angle of the strut and lower arm, typically, lowering the car 1" will lower roll centre 4" or so. Not good.
Getting them to combine with varying struts:
Subaru widetrack inverted (saloon)
KYB Ultra SR STI inverted (saloon) front struts won't fit widetrack
KYB Ultra SR non-inverted (available for wagon and saloon) front struts won't fit widetrack
KYB agx 4-way adjustable non-inverted (saloon) front struts won't fit widetrack
Koni inserts (rear insert available for bug or blob/hawk)
Feal fixed perch struts (slotted for use with wagon and saloon. Also available for widetrack)
Pedders have no current plans to sell their widetrack saloon struts, separately from their springs.
Tokico (Hitachi) DSP-10 16-way adjustable (saloon) fronts won't fit widetrack
Whiteline roll centre kit KCA313 or the Superpro version TRC0002, are helpful.
Currently investigating, whether it's possible to remove 0.7 of a coil at the rear, and 0.2 of a coil at the front - to save weight, by changing wire diameter/materials. Yet still pass the longevity/stress tests.
For those that asked:
Reducing the number of coils does reduce the coil bind/weight. But, increasing the coils, increases elasticity. The spring has to reach coil bind and return to its specified free length.
If the design/material exceeds its elastic limit, then the spring won't reach coil bind, or will take a set, and not return to the specified minimum free length.
The WA/A2 springs have an increased free length, compared to a stock STI spring - to accommodate longer length, non-inverted, struts - koni inserts, AGX, Ultra SR etc. As well as inverted struts.
UK delivery - now due week commencing 19 March.
Last edited by 2pot; 01 February 2018 at 12:42 PM.
For those that asked:
Reducing the number of coils does reduce the coil bind/weight. But, increasing the coils, increases elasticity. The spring has to reach coil bind and return to its specified free length.
If the design/material exceeds its elastic limit, then the spring won't reach coil bind, or will take a set, and not return to the specified minimum free length.
The WA/A2 springs have an increased free length, compared to a stock STI spring - to accommodate longer length, non-inverted, struts - koni inserts, AGX, Ultra SR etc. As well as inverted struts.
UK delivery - now due week commencing 19 March.
I have a full set of KYB Ultra SR's
Still to buy springs and topmounts what you recommend
I was looking at Whiteline castor topmounts and Wr1 springs ?
The WR1 springs are S03/D5/001 - imo too soft, to be that low.
The S05/D5/001 are a higher rate
When lowering, you'll have to change the internal bump stops - assuming you've got the inverted version of the Ultra SR? Otherwise, you'll be riding on the front bump stops = poor ride quality and understeer.
Obviously I'm biased, but the WA/A2 will be £290 delivered inc front and rear bump stops, to match the chosen inverted, or non-inverted, strut.
I like the Whiteline off-set front top mounts.
I think group n rear mounts, on the road, are unnecessary. A new pair of the OEM rear mounts will be fine.
Why, you may ask, a bug rear top mount, on a blob/hawk rear spring?
The blob/hawk top mount restricted the spring design.
No additional sprung weight, as the dead coils are at the top.
The 2 plane angularity of the bug rear top mount is a closer mirror, to the lower strut perch - a more constant/even pressure on the closed/ground top coil.
These are the rear upper rubber isolators, required to match the bug rear top mounts: Subaru Impreza 92-00 Rear Upper Spring Rubber Isolator
The original rear bug rubber top isolators, are now being superseded by the above.
I've had pm's about the bug rear top mount set-up.
The top coil, of a rear blob/hawk spring has a 100mm id. The subsequent coils are a larger id. That's why the stacked coils, on a conventional higher-rate blob/hawk rear spring, are at the base - as below:
Making the top coils stacked, as WA/A2 rear spring, means using a bug rear top mount - which has a larger diameter, but, the same fixing stud pattern as the blob/hawk.
Bug rear top mount - 125mm id top coil v Blob/Hawk rear top mount - 100mm id top coil
OEM ride heights when new '04sti: 386mm front, 366mm (full tank) rear. Usually, 15-20mm sag with age - spring sag/reduced gas pressure/top mount compression (worse on blob/hawk rear top mounts).
^ 374mm front, 342mm rear. 225/45 x 17 + konis + oem sti springs + 6 speed.
^ Just after fitting: 364mm front, 364mm rear. 225/45 x 17 + koni + WA/A2 springs + 6 speed.
Awaiting height measurements after the bushes and dampers settle to their new ride heights/alignment.
Hi Ian
The feedback, so far, has been:
Dive and squat much reduced - which is to be expected - as the springing is now linear and stiffer.
Ride quality improved? - I have changed the bump stops compared to OEM (for both inverted and non-inverted struts) - shorter, more progressive, at the front and stiffer, shorter, at the rear (to reduce understeer on on uneven/undulating/slippery roads without automatically using a bigger rear bar). But, what I think is being noticed, is the change to OEM ride frequency - 'flat ride' is occurring at a 45% lower speed. So, the suspension is now settling, before the next road irregularity - that's my guess anyway.
So your front end is 22mm lower and your rear is 6mm lower? From a simple geometry point of view, that should equate with NO OTHER CHANGES to a slightly flatter cornering stance, less squatting into the rear corner. You should notice very slightly more body roll, but hardly noticable compared to the reduced rear squatting. Other changes to feel will be down to dampers, spring rate and castor camber changes.
That's right - as utilised on the RB320 - increased positive rake:
A, relatively, higher rear ride height moves the roll centre rearward, increasing rear roll resistance.
That, in turn, makes the front end roll more - helping turn-in response and reducing understeer.
Good to see they are willing to develop something so fast. I was lazy and already ordered some eibach work street s coilovers. However once old is off I'll strip them get them repowderc9sted and then maybe get the inserts and sell for a nice profit or have a long-term spares.
have they give u any indication of potential cost yet .maybe an initial group buy to help them recover r&d costs
Took 2 years to get the springs the way I wanted.
Obviously, the spring info is crucial to making the inserts + just maybe, they already have helpful, baseline, Impreza info, that they can draw on.
I need to see the curves and some real world testing.
I never ask how much the prototypes cost...stops me getting them made.
Retail - off the top of my head:
£100 each they'd sell easily.
£200 each very limited market.
That's right - as utilised on the RB320 - increased positive rake:
A, relatively, higher rear ride height moves the roll centre rearward, increasing rear roll resistance.
That, in turn, makes the front end roll more - helping turn-in response and reducing understeer.
When you say a relatively higher rear ride height. is this 10mm, 15, 20mm etc. Is there an ideal amount of difference to aim for?
It's so you can mitigate against understeer, without using too large a rear bar.
When using road-specific spring rates, don't go too low at the front. That will depend on the bump stop length/stiffness, damper ratio (rebound to compression) and coil bind.
Measuring from wheel centre to metal arch, 0-10mm higher at the rear.
On the sti, 386mm front, 363-366mm rear is still positive rake. The front bump travel was mostly taken up with a 60mm rock-hard bump stop (pitch control) - which Prodrive, when fitting their springs, suggest changing to a softer, 50mm stop, with a soft nose.
21 November 2017, 09:31 AM
WA/A2 04-07 GD GG STI Springs
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