Putting the STing into STi

How many times have you heard magazine road testers say “The Subaru WRX Sti is a great car but it does feel like it under steers a little too much when pushed hard through a corner”. Well, it is fact the Australian Design Rules (ADR for short) state that all new vehicles sold in Australia must under steer rather than over steer.

This is good news for the majority of motorist as it means they are less likely to get in an uncontrollable slide but what about the Australian performance enthusiast who, if they are anything like me prefer their car to be neutral or rear biased through hard cornering? Fulcrum Suspensions and TEIN Inc are coming to the rescue of performance enthusiast who places as much importance on tuning their suspension as they do tuning their engines.

TEIN Inc. In conjunction with Fulcrum suspensions have developed Australian specification coil-overs to suit Sti, Japanese imports and even some Australian sports sedans. Ok, TEIN already have the product so why not just use that you ask? The answer lies in the difference between Japan’s snooker table smooth highways and the bumpy, pot-holed roads we have in Australia. No other Japanese coil-over manufacturer has been to Australia to undertake Research and Development (R&D) to my knowledge.

After fitting the TEIN suspension, the pilot of this Subaru Sti should expect a better relationship with the road and track, even when road conditions start to get a little bumpy the TEIN Super Streets will remain much more neutral and give the tyres more contact with the bitumen, hence increasing the grip when pushing hard through the apex. On the other hand our Subaru driver can experiment with full tail out oversteer using the damper adjustment dial. Either way he will be reaping the benefits of a more tuneable chassis that is suitable for our tough Australian roads.

The ‘after’ photos show a noticeable drop in the ride height which gives the Sti a much more aggressive stance.

Fulcrums R&D Manager, in conjunction with Mr. Ipeii Sugano, TEIN USA’s R&D manager, test drive the MY05 Subaru WRX STi on Fulcrums local test road to check out ride behavior while still it is still wearing the standard STi suspension. Any small nuisance soon become apparent using the series of bumps, potholes and corrugations on Fulcrums test drive.

Ippei measures the stock ride height from the centre wheel to the guard. This is the best and most accurate way to measure how much lower the new suspension should be. Photographs are then taken for before and after shots. TEIN’s R&D team takes similar photos to this with every car they install their suspension in for reference purposes.

Prior to installation Fulcrum test the TEIN Shocks on the Shock Absorber Dyno, which like an engine dyno measures the rebound and bump performance of the shock absorber. Fulcrum decided the information on the dynograph printout meant the rebound rates in both front and rear shocks needed to be changed to become a little less stiff.

Ippei dismantles the TEIN shock using a special service tool and pours shock absorber oil into vessel for re-use.

The inserts are removed and ready for the re-valving process.

Ippei puts the foot valve back on the shaft with new shims. This is only part of the re-valving process. The foot valve sits on the bottom of the strut and uses the same shims as the base valve which is the main, bigger valve that sits towards the top of the strut. The application of the car will ultimately determine what valve rates you will need to use. i.e. if the car is being set up for drag racing than it is more ideal to have a softer set up on the rear to allow for better rearward weight transfer, if you are setting it up for drift the rear should be quite stiff to allow the wheels to gain brake traction a lot easier while still retaining a modicum of control.

The base valve requires a new shim set up to reconstruct the valve. Fulcrum & TEIN together devised the recipe for what shims (size and type) must be used after testing the car on road and more specifically on the shock absorber dyno. Getting the valve rates correct plays perhaps the most important role in this part of the development.

The base valve shims laid out in order, the size, thickness and style of shims determine the damper and rebound characteristics of the shock absorber. After re-valving the sock absorber is pressurized when sealed.

Ippei dissects the OEM (Original Equipment Manufacturer) Sti struts for the comparison to the TEIN units, again all data is filed and transmitted to TEIN HQ in Yokohama. The importance of checking all the specifications of the suspension that comes out of the car is to ensure that it is in fact an OEM product.

Ippei fits the OEM shocks back into the car minus the springs to conduct more testing. Checking the standard drop is crucial to determine the full length of travel of the OEM units compared to the TEIN units. Generally speaking the TEIN suspension will have another twenty millimetres of bump travel over standard OEM units.

This time and with the wheels bolted in place Ippei, using a trolley jack compresses the shock absorber to its minimum compliance to check the clearance of the guard. He also needs to check the minimum centre wheel to guard measurement.

Ippei replaces the OEM units with the TEIN suspension (still minus springs) and performs the same suspension travel and guard clearance tests with the upgraded shocks.

Ippei sets the TEIN suspension up with the springs for its installation. Generally speaking the drive in/drive out installation of coil-overs is a quite simple affair and TEIN’s philosophy is to keep it that way. Even though it is fully adjustable it will be delivered to the consumer as a ready to go kit. You won’t need to adjust the ride height as it is preset to comply with Australian compliance regulations.

The dial on top of the TEIN strut controls the damper force. There are sixteen settings of which number one is the firmest and number sixteen is the softest. This particular photograph shows the pillowball mount which gives control over the camber settings for the front wheels.