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WA/A2 04-07 GD GG STI Springs

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Old 21 November 2017, 09:31 AM
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2pot
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Default WA/A2 04-07 GD GG STI Springs

While waiting for Eibach UK to release the WA/A2 springs, I've received a few questions. Hope the following helps.

I grabbed some images off the web, before Photobucket died. If it's your present/previous car? Thanks for the initial inspiration.

OEM STI



Prodrive 05 STI red S05/D5/001



JDM STI pinks



RB320 suspension



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 ).

Widetrack OEM sti front ride heights compared to :
Prodrive 05-07 sti red S05/D5/001 -18mm
WA/A2 -25mm
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.
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Old 21 November 2017, 01:43 PM
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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.

Thus lowered cars require stiffer springs and/or ARBs.

The Impreza is actually quite sensitive to changes. With my Coilovers, I can raise or lower the car 5mm and feel this roll axis changing.

Just 5mm.

I think, honestly, if you want to lower the car, it's mainly aesthetic reasons because of the amount of arch showing at the front. Am I right?

Lowering the front to give a balanced arch to tyre gap, will make the roll axis far steeper, and the car will indeed roll into the front corner.

Best way to compromise and fix that IMHO- The Whiteline Roll centre correction kit.

This allows you to drop the front with no penalties, except for scraping the nose on kerbs....

Nice pictures. Good work Sir.

Last edited by Markyscoob; 12 August 2018 at 03:10 PM.
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Old 22 November 2017, 11:59 AM
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Thanks.
Slowly drove me insane developing them

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.

This is an interesting read - Subaru v Prodrive suspension design:
https://www.pcadynamics.com/app/down...he+Insider.pdf

Last edited by 2pot; 25 April 2018 at 08:36 PM.
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Old 17 December 2017, 03:55 PM
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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.
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Old 18 January 2018, 09:19 PM
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^No, it's not possible.

After pre-production machine stress testing: 0.25mm increase in wire diameter. Slight increase free spring lengths.

Order placed.
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Old 01 February 2018, 12:38 PM
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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.
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Old 01 February 2018, 03:02 PM
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Originally Posted by 2pot View Post
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 ?
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Old 01 February 2018, 08:29 PM
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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.
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Old 02 February 2018, 10:06 AM
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^ Have you got a bugeye sti?
Did you buy bug or blob/hawk Ultra SR struts?


Last edited by 2pot; 25 April 2018 at 08:45 PM.
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Old 26 March 2018, 02:05 PM
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2 years work.....currently being split into individual sets.


Last edited by 2pot; 26 March 2018 at 02:09 PM.
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Old 29 March 2018, 01:42 PM
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Old 11 April 2018, 11:42 AM
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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.
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Old 23 April 2018, 12:20 PM
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Protective tubing, for the dead coils, due in. Needs applying, then these will be for sale at 290 a set - inc matching bump stops.
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Old 24 April 2018, 02:07 PM
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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.
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Old 25 April 2018, 05:04 PM
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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

Last edited by 2pot; 26 April 2018 at 12:09 PM.
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Old 14 May 2018, 08:53 PM
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Working out where the clip tubing needs to be, at the rear ride height




Just the fronts to do now.
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Old 16 May 2018, 04:54 PM
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Old 25 June 2018, 10:39 AM
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OEM ride heights when new '04sti: 386mm front, 366mm rear. Usually, 15-20mm sag with age.


^ 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.

Last edited by 2pot; 25 June 2018 at 06:03 PM.
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Old 03 July 2018, 12:29 PM
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After 120miles: 364mm front, 360mm average rear.

Further height measurement, at 300 miles, after bushes and dampers have settled + a new alignment.
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Old 29 July 2018, 12:12 PM
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Hi 2pot

How are things going with the new springs. What's the handling like.

Ian
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Old 29 July 2018, 01:45 PM
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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.

Mark
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Old 30 July 2018, 09:19 AM
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Originally Posted by 2pot View Post
^ Have you got a bugeye sti?
Did you buy bug or blob/hawk Ultra SR struts?
Sent PM
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Old 12 August 2018, 03:18 PM
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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.

Enjoy!
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Old 12 August 2018, 05:30 PM
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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.
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Old 17 August 2018, 09:16 PM
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Last edited by 2pot; 05 September 2018 at 09:12 AM.
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