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07-23-2011, 07:04 PM | #1 |
Scooby Specialist
Member#: 203474
Join Date: Feb 2009
Chapter/Region:
MWSOC
Location: Germantown, WI
Vehicle:2005 STU STi #46 PSM |
First autox day with new setup.
So after my first autox with the car today I learned alot. Was able to shave off about 9 seconds from my first run to my last run just by getting comfortable with the car and upping tire pressures. One thing I noticed though was through corners it felt as if the back end was skipping under hard corners. Any ideas? I feel that I am possibly lifting a wheel but not totally sure. Any help would be great.
Mod list: -Tein Monoflex 10k/8k -Cusco 22mm adj. sway bar set to medium setting -Whiteline swaybar mounts -Dunlop Direzza z1 star specs on stock wheels Thanks
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07-25-2011, 10:41 AM | #2 |
Scooby Guru
Member#: 442
Join Date: Oct 1999
Chapter/Region:
NESIC
Location: RI/SE Mass
Vehicle:17 Imp Spurt 00 S2k |
Skipping is sometimes caused from too bumpy a lot vs. too much spring/valving in the shocks not being able to soak up said bumps.
The adjustable bar, front or rear? A sway bar generally takes away from the capability to have an independent suspension and provides resistance to the rebound valving of the shock as it tries to push down to keep the tire on the ground, especially in the rear where the rear suspension becomes unloaded more than the front. High spring rate, less bar. If it is in the rear, disonnect it for the next event and see if that fixes the skipping. 8k/10k springs doesn't need much rear bar, if any at all (Stock bar was sufficient in my car with Tein RA 10k-F/8k-R, not to mention 10k-F/12k-R in my old wagon). Just be ready for a differently handling car... you might like it. --kC |
07-25-2011, 02:13 PM | #3 |
Scooby Guru
Member#: 60082
Join Date: Apr 2004
Chapter/Region:
MWSOC
Location: Minnesota
Vehicle:2004 Forester STI Silver |
Skipping how? Are we talking about spinning up a rear tire or are we talking about the back end of the car hopping sideways?
Does this happen on corner entry, mid corner, or exit? Does it happen under braking or throttle? Have you upgraded any bushings or added any chassis bracing? I ask because 10k and 8k is getting pretty stiff, stiff enough that suspension bushings and even chassis flex because a major part of the "give" of the car. Any freedom of motion you have creates sloppiness and an ability for the tire to move in some odd way. These are the kinds of things that allow wheel hop in a car. I would also understand the coilovers better. Do research on the damping rates and profiles. Do research on the amount of travel they have as well as the amount of travel they use up during cornering. You may have to tweak the preload and damper settings to optimize what you have. Hopping is often a concept of too much freedom of motion. Besides squishy bushings and an easy flexing chassis, spring rates (including using bump stops) and damper settings will play their role in how freely the tire can move. If the tire is given the freedom to lift or bounce off the ground, you're hopping. Often these coilover sets use very low compression damping and make moderate use of high spring rates and bump stops. The low damping means the tire can freely end up in the air due to low compression control. It's good for compliance and comfort, but it's bad for performance. KC pointed to one of two possibilities. If the damping, spring package, and more often the lack of bump travel limit what the car can soak up, you will end up jarring the chassis so significantly as to push the whole car up off the ground and subsequently make the tires airborn, partially due to very high rebound damping which is also commonly used in conjunction with low compression damping to control the chassis. This often requires one to go over something like a washboard road at speed. This is not something you would commonly experience at an autocross unless the surface was very rough, torn up, and patched. You will know when this is happening because it requires the surface roughness to upset the entire chassis (whole chassis shuddering quite heavily). I am more inclined to think the other way in that too much compliance is the culprit. This is along the lines of above with low damping, too high of spring, soft bushings, and lots of chassis flex. These things cause issues at spring rates much lower than you run and only get worse as you go up. If you haven't addressed these yet, these are likely your issue(s). You should at least have a rear strut tower bar and front fender braces(think the STI comes with a light fender brace stock). You really should be running very hard or solid bearing type connections with your lateral links, trailing arms, and if available front arm rear bushing (often replaced as ALK athough change in geometry changes auto-x classing). You will likely prefer to have the rear subframe bolts installed too. Get rid of the play, and the car will operate much more solidly and precisely than it does right now. |
07-25-2011, 02:25 PM | #4 |
Scooby Specialist
Member#: 33526
Join Date: Mar 2003
Chapter/Region:
MWSOC
Location: Brookfield, Wi
Vehicle:2013 WRB W/Gold BRZ 08 STI WRB w/Gold, 02 WRX |
Next event I will hitch a ride to see what it's doing.
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07-25-2011, 09:03 PM | #5 |
Scooby Specialist
Member#: 203474
Join Date: Feb 2009
Chapter/Region:
MWSOC
Location: Germantown, WI
Vehicle:2005 STU STi #46 PSM |
Hey Bart it was just the one corner before the long slalom on saturday. After walking the course on sunday I saw it was just the pavement that was making it do that. Sunday it was perfectly fine. Sundays course was TEN times better.
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07-25-2011, 10:18 PM | #6 | |
Scooby Specialist
Member#: 203474
Join Date: Feb 2009
Chapter/Region:
MWSOC
Location: Germantown, WI
Vehicle:2005 STU STi #46 PSM |
Quote:
Im going to take it down a notch once my endlinks get here and run the soft setting on the rear bar. |
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