Pretty in pink
After busting the left front strut of my car at Mazda Raceway Laguna Seca in November, I was presented with the
burden privilege of upgrading its suspension. I was hoping to have the upgrade done before I went to Laguna Seca, but the JDM (Japanese Domestic Market) STI (Subaru Tecnica International) springs I ordered in late July. The problem is that they didn’t arrive from Japan until after I had to get the car ready to go to Monterey. I ordered Koni adjustable strut inserts a little before I ordered the springs. They came within a week and sat in the house for the next four and a half months.
The springs that were on the car previously were Prodrive lowering springs. Prodrive is the U.K.-based company that prepares and runs the Subaru World Rally Team in the FIA World Rally Championship. The Prodrive springs are actually Eibach springs that are manufactured to Prodrive specifications. Prodrive has never released the spring rates for their springs. The closest they’ve come is saying that they’re 25% stiffer than stock. The stock spring rates for a 2002-2007 USDM (United States Domestic Market) WRX Sedan with a 5-speed manual transmission are 163 lb./in. front and 119 lb./in. rear (there’s a great list of spring rates on NASIOC.com (North American Subaru Impreza Owners Club) here). 25% stiffer spring rates translate to roughly 204 lb./in. front and 149 lb./in. rear. They supposedly lower the car 20 mm, but I’m pretty sure that number isn’t accurate because they lower the front more than the rear to create the “even” fender gap look.
Those, my friends, are the JDM STI pink springs. They have spring rates of 257 lb./in. front and 217 lb./in. rear. Compared to the Prodrive estimated spring rates, they’re 26% stiffer in the front and 46% stiffer in the rear. For reference, stock 2004-2007 STi/STI spring rates are 224 lb./in. front and 195 lb./in. rear. They lower the car 1 inch in both the front and rear from the stock (STi/STI) ride height. As a result, my car now has a saggy butt look. But that isn’t nearly as important to me as it being able to handle better!
Because the car got stiffer springs, it would be a bad idea to couple them with the stock struts. The stock struts don’t provide enough damping for the springs. This is where the Koni adjustable strut inserts come into the equation.
The part laid flat in the above image is the Koni Sport adjustable strut insert. The item positioned in an upright manner is an actual strut assembly, which is not available for the WRX. To install the Koni strut inserts, Suby Specialties had to remove all four struts, cut and drill into them, remove the original cartridges, and then install the new strut inserts. Because of their adjustability, a broad range of strut damper settings are now available to me. Out of the box, I believe there were set around 40-60% firm. At these settings, most of the body roll the car would previously exhibit in turns had been eliminated. The tradeoff was the ride was annoying on bad (read: pothole-ridden) roads. Wanting to soften up the ride, I adjusted all four inserts to an almost full soft setting. The car feels like it rides better now than when it was on the Prodrive springs and stock struts. Then again, that may simply be all in my head. The beauty of the ability to adjust the inserts is that I’ll be able to firm them up the next time I take the car to the track!