[maxwolfinger]

Well, as per the stock class rules of SCCA Solo II, I am not allowed to change the rear sway-bar. I am, however allowed to change the front sway-bar. My question is, would this help at all. I realize that reducing the roll in the front would increase understeer under normal circumstances, but if there is excessive roll, the tire contact patch is reduced, allowing less grip. I could also go the other way with a softer bar to increase front roll. So what do you guys think? Perrin has an adjustable front swaybar, so perhaps that would help?

 

[[email protected]]

Front anti-roll bar should help, even though we have not tested that yet. Like you mentioned, because there is excessive roll, an anti-roll bar should help without too much increase in understeer. Another way to put it would be: increase in understeer will be less than the increase in front tire patch, hence grip; yielding a net increase in front handling.

However, I would suggest waiting until SCCA decides on how to classify the STi in SP. If they decide to leave it in ESP, then I would suggest a full SP modified setup as you would be more competitive. Being competitive in stock form against Evos is tougher in my opinion.

 

[chrisw]

Adding a bigger front bar helps with the understeer on the initial turn in. The increased resistance would also add to the overall spring rate in front which would help control the body roll.

I have thought about using a smaller front bar to get more oversteer, but without changing the spring rates, I don't see this as a very practical solution, but I am still working on that problem.

 

[TrackRat]

I read all of the above posts with interest. I have not yet run my STi on the track yet, so I can't speak from a firsthand position. However I do feel the initial turn-in "Push" from fooling around on the back roads.

I can make the following general points FWIW

Adding more roll stiffness to the front of the car, either with a stiffer front ARB, or with stiffer front springs, or even higher tire pressures will make understeer greater, not reduce it. By making the front stiffer (as compared to the rear of the car)-by either stiffer springs or stiffer ARB- you are transferring more and more of the car's weight to the outside tire when cornering hard. As a result, less and less cornering force is provided by the inside tire. Once that outside tire gets to the point of cornering force "overload", you start to "push" in a big way. The "magic" is to have the inside tire in contact with the ground and providing cornering power.

Consequently The suspension adjustment to make is to "soften" whichever end of the car that is not "working" correctly. In the case of steady state cornering understeer, soften the front - either the ARB, springs or tire pressure differentials from F to R. The Perin adjustable front bar that maxwolfinger describes sounds like a great piece to add to allow quick adjustability while "at the track" for those autoX or track days. I will put that on my christmas list...

Is the body roll so great when driving the STi on the track that you are wearing or chunking the outside eges of the tire? As you watch some production based race cars thrashing around, you will see mild to moderate amounts of body roll. What Production cars do is to add negative camber to keep the tire patch as flat as it can be with the body roll that the optimum spring rates give the car.

For the first track day with the STi, my plan for now is that I will start off with it in "as delivered" condition, but have an accurate 4 wheel alignment done, with perhaps an added degree or two of negative camber to F & R. I have to believe that the Subaru Suspension wonks did a reasonably good job on the set-up, but likely erred on the conservative, understeering side as a matter of company policy.

One of my tuning mantras/rules is: "one change at a time". I believe the adjustable front ARB would be a good place to start.

 

[[email protected]]

TrackRat - Your comment about increasing front stiffness creating more understeer as a general theory for chassis tuning is correct. However, chassis tuning is not a linear equation. The reason a stiffer front bar would help is because suspension deflection in stock form is so large (significant positive camber gains during turns) that the disadvantages of understeer are easily offset by allowing the tires to stay closer to vertical to the road surface. In other words, the traction gained with less suspension deflection is greater than the load-induced loss of traction yielding a net positive increase in handling.

Once you achieve the point in which you all you can to minimize deflection, then increasing the front A/R size will yield more understeer for precisely the reasons you eloborated creating a less desirable solution

Because the equations are not linear, a lot of people reading msg board posts get confused. It is all relative.

 

[TrackRat]

[email protected] --Thanks for the response. I recognize that you have to "thread the needle" so to speak by trying to hold to the autoX rules and making only the changes allowed in the rules: ie front ARB mods only and keeping the stock springs and ride height. Ya gotta work within the rules... hence the narrow window to try and make this suspension work better for the autoX. Minimizing the suspension travel to a range smaller than stock to where the camber changes work to, or closest to your benefit, is the approach that you are taking. Sorry, I can't offer any first hand info to the discussion in that area- I havent even driven this car on the track yet. However, I will be watching and reading to try and learn more from others experience.

Sounds like we need to find someone who will prepare a camber curve chart on the STi suspension to really understand what is going on. With that info in hand, one could then set ride heights at an optimum, then spring rates and finally tune with an adjustable ARB. Of course, if there is "kit" available (like the STi "pink" springs ?) you can purcase a more agressive, less forgiving set-up "in a box" and install it with hopefully good results. However, the car is so new to me and the market, that I do not have a sense of wether such a "kit" is available for the US spec car. Since I typically run open track events, I am open to spring changes or whatever may improve the car-these are changes that may or may not be available to the autox classes.

As far as non-linear, I'm with you completely in concept. In fact, this car has the broadest change in dynamics from corner entry, throug the apex and to track out that I personally have driven so far. THis will be my first foray into AWD on the track, and I can't wait to thrash this puppy on the circuit. I will have a lot to learn, and I believe the Perin front bar would still be a good step. I bought this car because it is so technically interesting and has so much character. I have not been disappointed.

My Blizzaks did not arrive today by UPS, so with the snow forecast for CT this weekend, I have to drive a Suburban. I would have loved to go out and play with the STi instead.

 

[[email protected]]

TrackRat - Your thinking is on the right path. Every chassis change has to be tailored to the driver and purpose. There are many who auto-x and of course our suggestions have to take in to account the SCCA rules, but we also target track use. Our solutions will just come short of club racers, we do not target that market and it requires significantly more R&D budget than we or multi-purpose car owners can afford.

In fact, we just came from VIR and we are finalizing our track testing notes. We will post the report at our web site. And I think we are quite close to identifying various levels of improvements. THE issue to solve: body roll It is terrible for track use.