williaty

This is going to be a VERY long post, so I'll try to front load it with the questions and then hopefully provide enough information lower down so that you can get a complete picture of the chaos in my head.

My question boils down to: How can I increase oversteer? Read on for the details of what I've already tried.

Over the last month, I have made the first round of modifications to the car. In the end, I achieved the handling balance I wanted. However, doing so destroyed the ride quality and destroyed the car's ability to deal with rough surfaces like bad pavement or gravel roads. What I'm looking for are ways to achieve the handling balance I want without the penalty of making it only work on polished glass.

I have a '05 2.5RS Wagon. As we all know, it understeers like a hyena when it comes from the factory. I don't like that, no not at all! Working with this car has put the handling characteristics of my old car into perspective. I'm used to a car that, if you lift out of the throttle at all with the steering wheel anywhere other than straight, you had better already be snapping in lots of opposite lock or you _will_ be swapping ends. While I do not want to go to that extreme, I do want a car that will, when you lift off the throttle, tuck the line and, when you press into the throttle, ease out above the line.

In my quest for this I have maxed out the negative camber in the front, diddled with the air pressure, gone to spherical bearing rear end links, installed a 22mm adj RSB, and installed a rear STB (not that that affects over/under- steer, just for completeness). With the RSB on the 20mm setting, the front end grip was massively increased, but no matter how badly I upset the car mid corner, it would never even think about breaking the back end loose. Moving to the 22mm setting on the bar, not a damned thing changed other than the rid got harsher over bad pavement. Moving to the 24mm setting, I finally could adjust the car the way I wanted to. It was Nirvana! Lift off, glide in, press in, glide out. What more could I ask for! As it turns out, quite a bit...

However, there was a disturbance in the force. On glassy tarmac, the car displayed remarkable handling characteristics. Eventually, though, I noticed that there was an odd bounciness to the ride under HEAVY cornering loads. It felt like a very small scale version of the trick the Hondas do where they put really short, really stiff springs on and then rock back and forth like a hobby horse every time the hit an expansion gap in the freeway. It got worse from there! Rough pavement or a gravel road totally destroys the car's composure. Get on something requiring independent suspension movement and the car looses all grip and just knocks the crap out of me. The car, basically, is useless as anything other than a track car at this setting. I've backed off to the 20mm setting, which makes me want to cry because it feels like so much is missing, but at least the car is drivable in the real world.

I need to come up with a way to reduce understeer/increase oversteer without increasing the torsional stiffness of the RSB. I know two ways to do this, but they have downsides. I could:

1) Change the rear tire pressure to reduce grip. Downside: Premature tire wear and reduced grip.

2) Buy camber bolts and reduce the rear negative camber. Downside: Premature tire wear to outside tread block and reduced grip



What else should I be doing?

meilers

Are you experiencing bump steer? If you are still on the stock springs, it is unlikely that just a RSB would cause changes in the spring compression or behavior, regardless of the setting. Changing the camber in the front suspension can be a serious cause of bump steer, which does result in that "beat to hell" feeling on rough surfaces. Are you still on stock tires?

williaty

No, the stock tires had no outside tread blocks left after just 24k mi. I'm running Pirelli PZero Nero M&S's now. Bump steer is what? Do you mean hitting the bump stop and snapping one way or the other?

Ty

meilers

Bump steer happens when the tie rods of the front suspension aren't parallel to the ground, and the impact force on the wheels gets transmitted back up the steering column. It feels as if the wheel is being torn from your hands, and often the car also skips over the rough surface because the steering angle is changing rapidly. Literally, the ground is steering your car. The Impreza is very vulnerable to bump steer with aftermarket wheels/tires and strong camber adjustments.

You might want to try a front sway bar and front strut bar, setting the front sway bar at a "softer" setting than the rear. If you really, really want the car to rotate, you might also get some less grippy tires (say, some cheap Hanooks) and a Whiteline Antilift kit dialed in to the extreme. I don't think the camber changes you are making are working the way you intended; certainly I've never heard of behavior like that on the stock springs and struts. You could also do an engine swap and try for 350-400whp, which would let you break loose the tires in almost any situation

There are several different ways to iron bump steer out of the car; some are very expensive (changing tie rods or cutting custom ones, coilovers) and some are cheap and dirty. Lowering the car will by default change the tie rod angle; my car is lowered about 3/4" on Whiteline Ground Control springs, which are also progressive rather than linear, and this got rid of a lot of bump steer; however, this will eventually cost me my stock struts (which now occasionally hit the bump stops, something they never did before).