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Old 10-02-2009, 07:36 PM   #1
pignoseSTI
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Default Bouncing coming out of corners

Ok i'm having a bit of an issue with my car setup. Right now coming out of corners my STI starts bouncing(sometime uncontrollably). Feels like i'm riding a bull in a rodeo lol. This only started happening after I installed a cusco 1.5 way lsd in the rear diff, and it only happens on grippy surfaces(concrete). Here's my suspension info:

GC coilovers with koni 8611 double adjustables 700lb f/ 650lb r
Whiteline 27-29 fsb(on 27), Cusco 22-24 rear bar(on soft)
295/35/17 Hoosier A6 on 17x9.5" wheels 40psi f/44psi r
305/30/18 Kumho 710 on 18x10 wheels 31psi f/34psi r

Anyone else have this problem?
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Last edited by pignoseSTI; 10-02-2009 at 10:55 PM.
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Old 10-02-2009, 08:53 PM   #2
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Here's a video from a recent event :

You can see around the 25 second mark and 36 second mark it starts bouncing a lot. I just let off of the gas and it calms down but i'd like to power through all those turns. This video is with the 295's.
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Old 10-02-2009, 09:12 PM   #3
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It's almost like the diff is locking TOO much and fighting the rest of the driveline. Think of welded rear at low speeds.

Thoughts?
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Old 10-02-2009, 09:58 PM   #4
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Hmm I wouldn't think so. It's set at 60% lockup right now. I was thinking the rear inside tire is in the air and then i apply power and once the inside tire makes contact with the ground it upsets the car? It does bounce a bit less on the 18s, my guess is due to the shorter/stiffer sidewall(less basketball bouncing effect)? Just driving around on the street making u turns and such it doesn't seem to resist turning much. Slight chatter but it's the same as when I had the stock lsd
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Old 10-02-2009, 10:04 PM   #5
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Oh I forgot to put my shock settings. I usually run the front relatively soft for better bite. 3 clicks from full soft for compressions and about 1 1/4 turns from full soft for rebound. In the rear I usually put it sort of stiff for rotation. 9 clicks from full soft of compression and anywhere from 1 1/2- 2 1/4 turns from full soft of rebound depending on how the car is feeling.
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Old 10-02-2009, 10:33 PM   #6
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Any photos of the car during runs? Ones that might show the inside rear tire off the ground mid corner?

When I first starting running my STi with big tires in 2004, many of the national guys were actually breaking rear diffs as the tire would lift off, come down, lift off, come down etc. Keiko broke a couple diffs in 2005. Rear droop travel was severely limited on many of the coilovers people were running. It was on mine originally. I never broke a diff, but my car would experience some serious "pogo" style motions on corner exit. Fixing my rear droop issues solved the pogo.

something to think about at least.

Chris H.
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Old 10-02-2009, 10:46 PM   #7
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I agree with Chris H. I've driven a couple STi's with serious driveline chatter due to lifting the inside rear tire. Zzyzx coilovers solved this issue in my car (not an STi). These have a lot of droop travel.

To further suggest that this might be an issue, the soft front shock settings combined with stiff rear rebound settings will tend to lift the inside rear tire. Try turning up the front compression damping a click or two and reducing rear rebound. If shock settings are contributing to the problem, these tweaks will help keep the inside rear on the ground.

Andy H.
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Old 10-02-2009, 10:56 PM   #8
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BTW, what venue is your video held at? I haven't run any "local" norcal autocrosses since I've lived in Chico, so I'm not familiar with any of them.

PS: Hi Andy!
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Old 10-02-2009, 11:23 PM   #9
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Yo! I'd guess that's Alameda, but I dunno.
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Old 10-03-2009, 02:42 AM   #10
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Thanks for the input everyone! This was at Marina airport down by Monterey. It's teh only "local" site we have that's flat and pretty grippy concrete. Wish we could get Alameda but there's too much politics going on. The only club that can run at Alameda is the Porsche club unfortunately.

So basically stiffen the front to the point where the inside rear won't lift off the ground? I figure adding compression in front would add push wouldn't it? I will definitely try more front compression and less rear rebound at the next event to see if it helps though.
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Old 10-03-2009, 02:49 AM   #11
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I found this pic from the event, can't really see much though.
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Old 10-03-2009, 02:53 AM   #12
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Here's another but at this time I think i was running 800lb springs in the back. I switched to the 650s because someone said to soften the rear to let the car "set"
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Old 10-03-2009, 03:21 AM   #13
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Quote:
Originally Posted by pignoseSTI View Post
So basically stiffen the front to the point where the inside rear won't lift off the ground? I figure adding compression in front would add push wouldn't it? I will definitely try more front compression and less rear rebound at the next event to see if it helps though.
First find a real controllable testing situation. Then try all sorts of shock settings to see if you can make it better. Try disconnecting the rear bar. Try doing the right thing, then do the wrong thing...

My guess is that your problem can be fixed in the shocks.

Quote:
Originally Posted by pignoseSTI View Post
Here's another but at this time I think i was running 800lb springs in the back. I switched to the 650s because someone said to soften the rear to let the car "set"
Don't take this the wrong way but don't do something just because someone said so. You have to do testing.
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Old 10-03-2009, 03:41 AM   #14
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so my car does this as well when exiing corneres quick... my suspension is stock besides big sways and endlinks....
I figures its just gripping and the diff is tryin to sort stuff out so i dont really worry bout it. just keep ur foot down and the diff sorts it out for ya.. simple
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Old 10-03-2009, 02:15 PM   #15
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My first thoughts are for more compression damping all around. Are the dampers properly valved for the springs? Overly damped in rebound perhaps?

Jay
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Old 10-03-2009, 04:20 PM   #16
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Well I tried the 650lb springs and it did help. The car felt way better on most courses and more venues that I race at.

I've tried just keeping my foot in it but all that seems to do is prolong the bounce, and I don't really want to break anything.

The dampers are just the stock valving that come on the 8611's, same ones that come on the zzyzx setup.

I recently watched a video of stompy driven by Karen Kraus and that car seemed to do the same thing? And that car has lots of droop travel. Maybe i'll try disconnecting the rsb, but I don't want the car to push more. Right now it feels like it's turning just about perfect. I'd hate to mess that up.
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Old 10-03-2009, 07:43 PM   #17
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Tough to say. The spring rates are pretty stiff at this level and damper rates do follow. Other things start to show their flex like tires and chassis. The system just isn't rigid and will have some springiness to the parts.

Can it be improved? Maybe. Maybe not.

Try going a little softer yet on the rear spring. For the weight distribution of the car, the rear is still relatively stiffer. We're talking a 58/42 balanced car. A 700 lb. front spring would correlate to only a 500 lb. rear spring. You would say bye to oversteer until the sways were changed, but transitions would be more even, and the rear end would stay more planted. I'm not sure what the relative spring rates are for the STI sways. I played around with that for my car, but I know the STI runs different shapes and attachment points. For example on mine, equivalent swaybar rates would be a rear swaybar that is slightly bigger then the front bar. What you're doing now is running a relatively high rear spring rate to balance out the handling instead of a larger rear sway bar. It works either way I guess, but the heavy rear springs does create a less even dynamic experience. You're driving more with the rear end because it always sets up first.

What other hardware do you have on the car?

Upgraded any bushings/mounts?

Added any chassis bracing?

I'm just curious where you still have give in the car. If you haven't upgraded the driveline and chassis components, they'll just act like big rubber bands with that kind of power and stick. It'll be pretty darn sloppy relative to what it could be.
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Old 10-04-2009, 03:02 PM   #18
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Hmm I could go with softer springs in the rear to test it out(I have 500lb and 550lb springs in the garage). So you're saying go softer springs and bigger bars? I do have the big Whiteline bar I can put back in the rear. I thought going stiffer springs and softer bars would help the droop travel. I know when I had the big bar in the back I would 3 wheel into my driveway. Don't do that now with the smaller cusco bar.

So far I haven't done too much to the chassis/bushings. Right now I just have group n motor/tranny mount, TIC Rear diff and outrigger bushings(race), and 07 sti fender braces. Bushings were something I wanted to do for this season. I could do a rear strut tower bar, but I can't do a front(have gc top mount camber plates). Other than that can you recommend anything else that's SM legal?
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Old 10-04-2009, 10:43 PM   #19
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Sway bars can substantially limit travel. They limit roll by reducing the independence of the suspension. I run my car without a rear bar to maximize droop travel. If I put a rear bar on my car (any rear bar), it will become a tripod in corners. If a setup is achieving droop travel by using helper or tender springs, the sway bar will keep those compressed even when the wheel is in the air.

My car runs spring rates that are 800/600. Sometimes I use a front bar, sometimes I don't. The car weighs about 2600 pounds with 60% of that on the front axle. It is very well behaved.

One data point to consider.
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Old 10-05-2009, 01:11 AM   #20
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The rear strut tower bar will help a good bit in chassis stiffness. For the front, the big thing seems to be the fender cowl braces, not so much the strut tower brace.

How does your driveline feel? Does the engine feel locked to the road or is there still some bounce in it?

You'll be giddy once you get the suspension bushings + steering rack bushings done. It really makes a world of difference. Perrin should have a bearing type ALK available. There are really cheap adjustable, bearing type lateral link and trailing arm sets on eBay. I assume with the coilovers, the tops are solid bearing mounts front and rear.

GT Spec has front cowl braces and rear strut tower braces, even a partial cage setup for the rear.

Basically you're working to the point where the give is in the tires, not the car. Right now, the car is just a bunch of rubber bands bouncing around. Once you get the car locked down, this wills stop, and then the give will be more the tire in relation to the road. You'll also get a MUCH better sense of grip, braking, and acceleration with the upgraded bushings. Steering will also be MUCH more exact.

All this doesn't mean the bounce will go away. You are running a very stiff setup and working with high forces. Gravity will only resist so much.

As for suspension, I suggest a smaller rear spring simply for the matter of dynamics. For example, with a heavy rear spring, you need heavy rear damping. What this does is let the rear end react and finish first. It'll always set up before the front. It feels stable, but you start heavily driving with the rear tires. The front end probably feels a bit sluggish and mushy relative to the rear end. You make use of a bit of power or end up being aggressive with the car to help break the rear end loose. It's less natural because it always finishes reacting first.

As you soften the rear end, spring and damper rates follow. The back end starts reacting more evenly with the front end. The rear end starts to loosen up. Side to side transitions becomes more even front and rear. You start to drive with the whole car instead of the rear end. You start gaining some understeer though, but you fix that through sway bars. You can regain the understeer/oversteer nature but also maintain the even dynamics. It's simply a setup I personally like a whole lot although it's a very uncommon setup.

*** Warning, rambling ahead ***

I started way back with mild Swift Sport springs for my Forester. It ran a progressive rear spring, but it was actually relatively even (in the middle of the progressive range). It felt quite good driving though, but the progressive nature did limit behavior in a sport nature. I ended up going with Prodrive STI springs, something with a heavier rear spring. I ran that and even upped the rear sway, and kept trying to play with the car. I hated how it drove. It too would lift a rear tire and the front end was always sluggish. I ended up grabbing a set of RCE Wagon springs and ran the RCE on front with the Prodrive STI rear. This went back to the even setup again that I had with the Swift Sports. I liked this setup a whole lot. It was just too low since I also rally-x and need the car for winter, although I did "ice race" with the setup, and really liked the neutrality. I ended up finally going with Ground Control to regain ride height. I'm now half where you're at, 350 lb/in front and 250 lb/in rear. This is on D-Spec struts, so I'm limited by the strut to 350 lb/in. I do auto-x and rally-x with the car, and it's drives beautifully, and I'm not even done with the suspension. It still needs a slightly bigger rear bar, just 20mm/20mm front and rear (still needs to function well for rally-x). The car is nearly neutral and just a breeze to drive at the limit. I can't do much in auto-x and end up mid pack, 3400 lbs. with me in it and 150 ft-lb. to the ground. I'm going to win no trophies. However, in rally-x, I pretty much spank my local PA class and am now doing M4 and still capable of podium finishes. Dirt is the great power and weight equalizer. Moral of the long story, the car handles awesome, and for what it is, it's darn fast. It's a configuration I'm ecstatic about because it just functions so well.

For you, you run a pretty big front bar. I'm not sure if a big enough rear bar exists. For example, with the 22-24mm rear bar, I would suggest actually running the stock front bar as bad as that sounds. You'll need a rear bar that's equal to if not greater in the rear. They'll have to at least match in effective wheel spring rate. The 700 lb/in front and 500 lb/in rear springs will make the car even. Anything you do with the sways will change this to understeer or oversteer. You'll probably want to be running a pretty big bar with the spring rates you run. It depends on the relative front-rear and side-to-side roll stiffness you want. I'd say the stock 20mm-21mm front bar plus the rear bar you have will give you a pretty neutral end result with the 500 lb/in rear spring. It'll just be relatively weak for roll. You'll get little squat and dive because the springs have a lot of leverage front and back. However, cornering, sway bars need to make up for the shorter lever arm. It's not something I've personally toyed with yet, but I assume a car will behave more evenly when roll stiffness is more even in every direction. I would assume the car would handle in a more skewed manner if this is less then even. It's just a guess though. I've only been around stock for sways, and this isn't too bad for the spring rates I've been running as of recent.

You and adhowe70 did bring up good points about the sway bars. It really does depend on if you're getting so stiff that you simply start running out of travel range. If the car only uses 1/2" in either direction loading and unloading, is it really enough for the surface you run on. I can see sways as being a good method to help limit the side effects of very stiff springs. If it's better, I'm not sure. I'm not really sure if you're better off softening the springs and running bars. I guess it kind of depends on how you want the dive/squat behavior to be in relation to roll. I'm of the sense that side-to-side stiffness should be relatively comparable to front-rear stiffness. It just seems more...even. It just means that if you actually need and inch or two of usable travel, you may need to go softer. I'm not sure which is the more appropriate trade off.

Really, just give it a try and see how the car feels. I know going softer seems counter intuitive, but camber changes should help counter any added roll. I also don't know how smooth/rough the courses are where you compete, so I don't know if softer will benefit you paired to some of your less then ideal road surfaces. Try with and without sway bars. Run no bars, light bars (if you have the oem front still), and then the stuff front plus stiffer rear bar you have. See what you like and what seems to function better.

Last edited by Back Road Runner; 10-05-2009 at 01:18 AM.
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Old 10-05-2009, 02:16 AM   #21
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As another said it may be a good idea to check all the mounts and bushings. Even race bushing can tear apart with the loads your car endures.

Rob

Last edited by STirish; 10-05-2009 at 02:34 AM.
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Old 10-05-2009, 07:47 AM   #22
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Quote:
Originally Posted by oscargarza88 View Post
just keep ur foot down and the diff sorts it out for ya.. simple
Sure, if you dont mind buying a diff every other AutoX.

OP, hard to tell from the video, but is the car unpredictable when this happens? Do you find yourself having to correct for oversteer?

If I were you, Id go with your idea of disconnecting the RSB first.
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Old 10-05-2009, 01:14 PM   #23
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I'll second the disconnecting of the rear bar before changing anything else. Mine and a buddy's car are both on 8611's and we run STU with heavy-ish springs and little bars.
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Old 10-05-2009, 03:26 PM   #24
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Try running fun runs or an event with just STU spec tires, and not R-Comps. I've had a similar problem that you are experiencing. Non-R-Comp tires muted all the bouncing.
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Old 10-05-2009, 03:55 PM   #25
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just for reference so you guys know where the OP is coming from. he's a humble guy so i'll say it for him. pignoseSTI is a pretty damn good autocrosser. he is constantly in the top 15 times in a region full of national champs, fighting for TTD on good days.

sometimes i feel like neutral for the OP is actually a bit of oversteer. =P he likes the car loosey goosey so he can rotate. not sure if that's obvious to everyone.

sounds like the general consensus is that the rear end should be a little more compliant, specifically with regards to travel?
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