OK, it looks like I've scrounged together enough pennies to buy a set of GC coilovers for my car. But now I have to decide on spring rates and length. The car is my daily driver, but used for AutoXing on occasion. I'm planning to find a set of stock struts for the winter, so we don't need to worry about keeping it soft and squishy enough to not kill me in the snow and ice. The car already has Koni inserts with stock valving. Here's what I'm thinking... Spring Length: The car currently has a set of Eibach Pro Kit springs, which are alleged to lower the car 1" up front and 1.2" in the rear. GC offers a 7" spring that starts out with the car lowered by 0.75". This seems like a good choice to me. Spring Rates: I've looked around for info on a number of setups, with differing opinions on front or rear bias, how stiff to go etc. From looking at the chart on North Ursalia's site (http://www.northursalia.com/techdocs/spring/spring.html), it strikes me that STi must've done a fair bit of testing and number crunching before deciding on the rates for their Gymkhana springs. But I think they're still a bit soft. So, I scaled them up a bit to the 400 range. Keeping the ratios the same, I wind up with 420f/400r. Discuss/refute/recommend/advise/flame. Thanks, Stuart.
call redshift motorsports and ask them what Corey Ridgick was running on his old car, then copy that.
I think that was 450f/500r or 500f/550r. I think that running springs in the 500s is probably too much for the fairly bumpy surfaces we run events on locally. I'm trying to beat Larry, not take first at Nationals. Stuart.
E-mail steve G. or Neal. I would go with ~400f/450r maybe 50lbs higher front and rear. I think anything stiffer is a little too much personally. Larry is running 440f/400r I think. I think moderately stiff springs and decently sized swaybars is about the optimal setup for an Impreza. If you go too stiff with either springs or bars the overall performance will suffer. If we always ran super smooth surfaces (like Eau Claire a few weeks back) I think I might go with even 100 lb stiffer springs.
Larry's are rear biased, but I can't remember the exact rates. These are close, I think, but the other way around. I've got the 22mm FSB now, and an 18mm RSB. The RSB is next on the list of upgrades after the GC setup. Stuart.
I hate when I fail to live up to expectations, but honestly, I really have no data about the "hot setup" for autocrossing a Subaru with coilovers. My only serious autocrossing experience was in G-Stock. My current 2.5RS daily driver just has simple Prodrive springs. I'd ask Larry B. He just got new Konis and coilovers. He and his wife drove the car to Milwaukee, and he did quite respectably well vs. a very well-prepped STS Civic. So I gotta imagine his setup is close to what you're looking for. The #1 thing you want to watch out for is selecting a spring that is beyond what your struts can handle. You can have the same spring rates as Corey R, but if he's running custom re-valved struts and you don't match that, you could easily end up with a setup that is worse than what you have now. It'll bounce like crazy. I don't know what the range is for a Subaru... Neal
I talked to redshift about valving on the konis and their shock dyno readouts when I was shopping around for suspensions for my wagon and found that for anything under 300lbs springs the stock valving on the konis isn't much better than anything else. That being said it really looked like the sweet spot to get the best and broadest range of adjustability and have a decently stiff spring rate it was right about 400lbs, or pretty much close to what larry is running. GRANTED this would be for a significantly heavier car with more rear weight, we had figured on 450f/480r
According to Koni, their stock damping is good for springs up to 650#, but they suggest not running that on the street. Don't ask me to expand on that statement. Larry and I already argued about it and came to no good conclusions. I guess I'm looking for ideas as to how I can work out what is likely to be best *before* I plonk down the money; a magic formula, if you will. There must be a *reason* Koni chose the damping rates they did. There must be a *reason* STi picked the Gymkhana spring rates they did. This stuff doesn't just happen by accident. Or at least I hope not. If I can find some way to figure out what those reasons are, maybe I can better justify whatever choice I eventually make. And I don't want to just copy Larry's setup. That'd be lame. If I was going to do that, I might as well just co-drive with him. I just don't want to pick something based on faulty assumptions because I didn't do enough research ahead of time. Stuart.
If someone wanted to give me their corner weights, I could calculate out the theortical spring rate needed to achieve the critical dampening rate (given the dampening rate of the konis are semi-fixed). But then again, I'd have to make some pretty uneducated/unexperienced guesses as to what kind of dynamic loads you'd be seeing. And even if I had fairly accurate data, I can't really believe that the theoretical crytical dampening rate would translate to real time improvements. It would be kind of a fun experiment to see if it came out to somewhere near some of the common rates being discussed here though. My guess would start at finding the yaw angle experienced at load using the suspention travel, using the static corner weights, and using some sort of measured lateral g-force experienced and try extrapolate that to a dynamic force at each wheel... Any takers?
Erm, yeah, what he said. I wonder if Koni would give us the info you need on their dampers (which are rebound adjustable), and I think Larry did corner weight his car, so he might be able to contribute some numbers there. We could use a g-tech to get lateral gs. Yes, I agree, a fun experiment. Didn't I see some interesting suspension modeling software mentioned here or on the MAC forum a few months ago ? I wonder if that would help. Stuart.
just because it can handle a spring upt to 650# on the highest end doesn't mean you'll have any adjustability when you get there unless you get them revalved.
FWIW, I am running 500 f and r... I have a pair of 550s that I have thought about trying, but I need to eliminate my rear camber issue before I go that route. I think I would like 550s in back to reduce steady state understeer a bit, but we'll see. I wish it was easier to swap them out. There has been a lot of discussion about rates, but there really is no consensus. I have seen both front and rear bias setups that were competitive. I decided that I will never have the exact same setup as someone else so I have been doing everything on my own.... Everything is so inter-dependent that short of having some good datalogging, and more importantly, a good interpretation of the data, it is really a crap shoot. Tweak a swaybar setting....tweak valving fr or r....change tire pressure...etc. They all work together when you are judging seat-of-the-pants style. They don't call it a black art for nothing.
Adjustable rear lateral links are your friend. They should also bring those super wide tyres of yours inboard a bit so they don't rub. Hmmm, if the wheels moved inward far enough, you could put even wider tyres on there. I've had it suggested to me from a reliable source that I should get at least 400# up front, and then do the rear bias thing, so at least 450# in the rear. Goes back to cogitating... Stuart.
Since you brought it off topic... Rubbing on the fender is not the issue, it is rubbing on the lock collar of the coilover. I need to move the wheel farther from the strut to address it (need to move the hub away to address it completely :eek4: ). The last option is to put camber plates in the rear and "tip" the strut inboard, "countering" the increased camber at the hub interface. If I had 3-4mm additional clearance, camber would not be a problem. I am going to see how much I can add by getting the sidewall right next to the lock ring. Maybe that will work for now.... The only way wider tires are getting on is with a sawzall....that is not necessarily out of the question in the near future... :naughty:
Koni's (along with most other shocks these days) do not have a fixed damping rate. They have progressively lower damping rates depending on the piston speed. Combine that with the fact that you'd never want a critically damped spring on a car and figuring out the critical damping rate is pretty useless. You want it to be under damped on the bump side and slightly over damped on the rebound side.
True on both accounts. But how are you to know whether its over dampened or under dampened unless you know where the critical dampening point is? Like I said though, this would be more of a fun experiment than an actual way of setting up a suspension. The real way to do this is through trial and error unfortunately. Because everyone has their own driving techniques and tendancies. IMO the only way to dial in the perfect suspension setup is to get seat time on multiple setups. $$$$!!!
Very true. I went though 6 sets of springs setups on my car before I got to what I have now, and without going stiffer (which would require different damping rates) I think I have the best setup I can get for me. You can get 4 springs for $200 from eibach, any rate and length you want. A little experimentation isn't really terribly expensive.
