D2 Coilover Install
By Dave Clements (4/13/01)
(updates in italics)
No turning back now.
I had just got off the phone with Chris at TRi Tuning, I'd just ordered a set of the brand new D2 coilovers from him, and I was in a bit of a daze.
Normally I don't spend much money of a car after I've purchased it. Then again, this is no normal car. The Legacy Touring Wagon was sold for only 3 calendar years, between 92-94, and they didn't ship many over. Turbo, AWD, great interior.
Anyway, one thing led to another and for the first time I have a car worthy of these expenditures.
Having thrown the car around on the autocross course and having good success on short courses and those without neck straining hairpins and fast slaloms, I thought I was doing pretty good for a heavy, underpowered wagon with simple replacement struts and stock springs. I was, but I hadn't seen anything like what April 1st offered. This course was very long, had a lot of long turns and hairpins, and made my hate my suspension by the end of the day. Time for a change.
Basic suspension theories on struts maintain that the spring and shock keep the car from excess and rapid movement when traversing uneven terrain or when performing avoidance type maneuvers. The spring is the principal element in keeping pressure directed upwards and resisting compression. The shock more or less manages this function and assists. The spring "springs" back when the load is off and the shock tries to manage this rebound to keep it from reacting too fast or too slow.
Normally a car with a strut type suspension has a wide, tall spring of an all-around rate with shocks that do a nice, even job at keeping the ride nice and the spring in check. This is all fine and dandy, but when you really want to move fast, there's far too much play in the springs and the shocks are really very underdampened.
Lowering springs with higher rates are available for almost every car. They're a simple bolt-in procedure and they do a reasonable job for the price. Adjustable shocks are now becoming widely available, with the KYB AGX being the only one for Subaru at the moment. They offer 4-8 positions of adjustment that control both compression and rebound reactions. They do a fair job when combined with good spring, many people have this setup with AGX and springs from Eibach, H&R, Whiteline and TEIN.
A note about spring rates. I won't go into the progressive/linear discussion because I'm not qualified for that, but a spring is either evenly spaced between coils, or is more dense at one end. This either makes the compression even over the course of compression, or progressively stiffer, hence the terms. Spring rates are measure in pounds or kilograms, but we'll stick to pounds, it's what I know.
A 375 pound spring, the rate for the front ones on the D2s, is calculated to compress 1 inch per 375 pounds applied to it. Simple. You may think that sounds light, but we're talking about four corners of the car, and that only has to support around 1/4 the weight of the car on a level surface in an ideal situation. Since the engine is in the front, and the rear isn't as heavy, the rear springs are only rated 325 pounds. No biggie. These were meant for an Impreza or Legacy Sedan, but the rates are very high for something that light. The rate difference is approximately %15, while the weight balance is less, but that's where tuning comes in.
Enough with the techno-babble, on with the good stuff.
Coilovers are a combined assembly of shock and spring, not unlike the strut, but much more purpose-built. A very few cars in the world come with coilovers. This particular type uses a threaded body housing the shock with an adjustable perch for the bottom of the spring. By adjusting this perch, more ride height and a firmer ride can be achieved. It also allows for adjustable height through the bottom mount, as it's threaded and can be adjusted up and down on the body. This level of adjustment is complimented by adjustable compression and rebound settings. This particular D2 setup had 24 positions of adjustment, from mild to very hard. I won't go into how it does this, but suffice to say that it's changing how fast the fluid flows around in the body.
The combination of this adjustability, and the inherent stiffness of the setup meant that even totally detuned, it could be more responsive than my existing setup. It was.
Arrival of the set a week after I'd ordered them was a relief. All four were well packaged in a small box packed with Styrofoam peanuts. It included all four coilovers, fully assembled but shortened to fit in the small box. A bag with 8 nuts, two spanners for adjustment of the perches and two Alan/hex wrenches for shock valve adjustment were included. No instructions. Fun.