SPD Tuning Service

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Impreza WRX Factory Suspension FAQ (revised 990129)

Subaru has built a reputation for some very fine sports sedans. The FAQ will outline how to obtain these qualities offered in the non-US "WRX" cars, generally using Subaru, STI and Prodrive developed parts. It produces a responsive and supple handling car that will blast through all dips and enter driveways without crashing the chassis on the ground or crashing your head on the headliner. This FAQ is not intended to promote the best racecar suspension nor the best looking lowered car. Them's the rules.

To keep the FAQ short no discussion of suspension theory or other description will be given except to remark on the effect of a change.

Stage 1. Sway bars and standard replacement shocks.

First things first. We generally recommend an upgrade to the 18mm rear sway bar for most Impreza and Legacy owners. This 19f/18r combination gives the car a wonderful solid steering response with greatly reduced understeer.

Our Prodrive Eibach/Bilstein kit and our STI Version 5 kits mentioned below are designed around a 19 front/20 rear combination and exhibit near perfect balance. We sell a 20mm rear bar with every kit.

For the 2.5RS manual transmission owner, we offer replacement of the 15mm-rear bar with the 20mm rear bar fitted to the latest WRX. (93-96 WRX had an 18mm rear bar) This gives the car a much better trailing throttle brake and thus a better turn-in capability. Note that one must get out of the brake and into neutral or slight throttle to stop the car from rotating once you have turned in. Failure to do so can result in a slide or a spin, which is why the US cars don't come that way in the first place. The awful understeer under power is now reduced to a normal 4WD level.

Owners of non-rear sway bar Impreza can add the frame mount pads, rear control arms and fittings from a salvage yard Legacy or Impreza. You could use the 18mm rear bar from the pre-96 Legacy wagons, but it tends to bind and is not recommended. For stock and non-2.5RS suspension, an 18mm Impreza bar is strongly recommended. It worked quite well and could keep you out of the weeds, as the standard shocks and springs are not setup for the transitions the 20mm bar will give you.

There are bigger bars in the after market. Frankly, I do not see that they give you that much. They generate a increased lateral spring rate that attacks the damping ability of standard shocks. In a "tank slapper" situation this makes for some difficult control recovery problems. The solution to this risk is to run the car over dampened, which has a negative effect on the ride quality, See Paragraph One.

For those wanting a bit firmer ride, our WRX-RA replacement shocks seem to offer the best balance. I cannot 100% recommend them the rebound damping is too great for stock spring rates. They are fine for sport driving, but you had best enjoy a firm and at times choppy ride quality due to the over dampened rebound.  Above 60mph they come into their own. They are intended for WRX springs, which are available.

Stage 2. Springs and Shock kits.

Once the sway bar(s) are taken care of, there are two sets of suspension, the WRX STi Version 6 kit and the Prodrive Eibach/Bilstein kit. The Version 6 is a firm suspension with 20mm lower ride height from the US versions. It will be fine on the twisty mountain road or for the autocrosser on a budget. Just good plane fun. The Prodrive Eibach/Bilstein kit lowers the car about 20mm also and has received rave reviews in the British press and from RS .

In 1995, I took a ride in a Prodrive WRX with this kit installed. On 205/45-17 Pirelli PZeros you could flick it into a 100mph bend on a two-lane blacktop road and it just carved an arc... impressive. Not a bobble, not a twitch, just pure communication of what the backend and the front end were doing. Pitch it in to grind off speed and find the apex or turn it in and set in the groove. It does not matter, it responds to either style of driving. I use this kit on the SPD Tuning Service 260hp Impreza. Put it on one day for a test spin, never took it off. What more can I say?

There are three versions of fully adjustable LADA (BTCC champions w/Ford, FIA Porsche Cup cars, etc.) for the Impreza. At present these seem to be the preferred setup for the serious driver because they are externally adjustable. The rebound rates have been set by LEDA after extensive testing with the 2800lb Impreza Turbo. Rebound rates are set by the weight of the car, and the spring weight. This eliminates the need for independly adjustible compression and rebound on the unit.. For those what would want to minor changes to these fixed settings, a gas two way unit is availble. The LEDA is the stuff if you plan do see serious track time.

There are other after market units such as the GAB/Tokiko 1.75 lowered suspension with 400/300-pound spring rates. They are more money and have really stiff (as in objectionable) ride quality. They will produce a quicker time on a high-speed track, but you could probably run a twisty autocross track faster on less spring as they are too stiff and a bit too low. If you are that serious about a suspension,  LEDA or Prodrive Tarmac setting Group N coil-over suspension is the way to go. SPD Tuning Service does not recommend these rally type units for every day use. It will get old very fast.

In general it is not a wise move to purchase springs without also buying the shocks that have been developed with them. In fact, if left with a choice of changing springs or changing shock, I would change shocks. Stiffer shocks on stock springs is a better move than changing out your springs in hopes of better handling. An 18mm or 20mm rear bar is an essential change.

Stage 3. Rubber bits

Once the springs and shocks are in place the addition of the STI bushing set will give the car a very precise feel. This set included new motor and trans mounts, which improve the shifting and throttle response. Taking up the slack in the production bushings is perhaps a fine point for the $700 the set will cost, but it makes it possible to place the car very precisely on the cones when running an autocross route. The area it benefits the most is braking. An Impreza with WRX brakes, Prodrive suspension, P-Zero tires and the STI bushing set was tested at 105 feet from 60 mph. The lack of compliance in the bushings keeps the tires griping.

For the standard Subaru Impreza owner, the Subaru sport rim has been a 5x100mm 15x6 -55 offset for many years. http://www.tirerack.com has the Subaru alloys for $59/69 USD. These are some of the lightest wheels you can buy and with 205-55 or 60 series tires make a nice setup. We sell Toyo Proxes tires. Excellent T1 and FZ4 compounds. Toyo, and Bridgestone Expedia produce good lap times and are on our "recommended" list. Always better to have good tires on stock rims than dog meat on 17 inch rims. You heard it here first.

The 2.5RS uses 16in rims. The Prodrive road cars are fitted with 17x7 -50 Speedlines and Toyo Praxes T1, which are surprisingly good in the wet. The M+S rated FZ4 is 50% more miles at 80% the grip of the T1. We have Speedline and Raceline wheels. All SPD wheels are low pressure cast and heat treated wheels. There are several other rally wheels available, but they are limited production forged units that are $$$.

Send mail to mshields@spdusa.com with questions or comments about this web site.
Last modified: May 23, 2000