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PostPosted: Tue Nov 07, 2006 4:17 pm 
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Location: orlando, fl
Okay, I have been trying to figure this one out for a while.

At the track, I'm cruising along at close to top speed...Corner is coming up...
I brake, very hard, for the corner...
The car shifts to the left! :shock:

It is almost like it wants to turn left. I always have to correct with the wheel.

Doesnt seem a problem at lower speeds.

This may be tied to the fact that the car is somewhat twitchy at higher speeds...say over 80mph.

I have poly bushings in the lower arms with lots of postive caster, which should help with this sort of thing...

I cannot remember if it continues to want to pull left after the initial shift...If so, I would think it would imply brakes are uneven from left to right.

I cant imagine what would cause it to always want to pull one way, and not the other...maybe it is the brakes.

I pulled the front brakes and replaced the pads a few days ago. I made sure the sliding pins were lubed and good to go. The brakes seemed fine.

I will check the rear brakes tonight.

Everything on the suspension seemed tight.

Plan to be at Road Atlanta on thursday for a test day. Give me some ideas and I will test them on thursday...

I am waiting on a custom lower front strut brace from Murr, and am hoping this might make a difference.

thanks,
matt


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PostPosted: Tue Nov 07, 2006 4:42 pm 
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Location: orlando, fl
oh yeah,
the alignment is about an 1/8th inch toe in rear...about zero toe front


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PostPosted: Tue Nov 07, 2006 5:24 pm 
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matt,

i think that what you describe about the car's line shifting is due to the increased front caster and the rear toe settings. my car seems to do the same thing after i installed all the poly bushings, whiteline caster bushings, and dialed up the rear toe.

it seems like the thrust line adjusts itself, probably from the increased rear toe. the initial turn-in with the increased caster in the front geometry takes a big bite, the rear end twitches, and the car blazes through the turn. it was wierd to me the first time i drove my car after making all the suspension changes at one time but i'm getting used to the new handling pretty fast.

i also swapped my sway bars with the front and rear going to the largest available diameter of aftermarket sway bars. i also used red pro-thane end link cushions, they are way harder than the purple/ blue ones i got from whiteline. even with the front sway bar in place, i can get the rear end to rotate while before i couldn't shake the rear end out of line no matter what i did with the controls. i'm looking for improved autox lap times although i won't be able to tell until the start of the next season. we're shut down for the winter here.

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PostPosted: Tue Nov 07, 2006 6:23 pm 
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Location: orlando, fl
Ok,
so are you talking about turn in...as in just after turn in on a corner?

It does it in a straight line.

Does your car also do this in a straight line?


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PostPosted: Tue Nov 07, 2006 7:20 pm 
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Matt, first of all, do you really need rear toe? I run zero toe front and rear.

I also have this problem, but quite honestly I think it's a combination of the cars somewhat poor weight distribution (biased to the front), and too much rebound damping in the rear.

Obviously we cant do anything about the weight distribution (nor the resulting weight transfer to the front wheels under heavy breaking, unless you just want to brake less :) ), but I do plan on cranking down my rear koni's a little next season (although my car is sprung so softly/poorly that I don't need a whole lot of change).

In anycase, can you dial down the rebound damping?

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1989 Suzuki Swift GTi - ITB Racecar
2000 Subaru Impreza 2.5 RS - Daily Driver
2004 Dodge Ram Pickup - Tow Vehicle
2006 Suzuki DR-Z400SM - SuperMoto
2009 Cannondale Rize
I rarely visit TeamSwift anymore, so please email me if you have a question. On average I'm only checking my PM's here once a month. "roy (at) forcefed4 (dot) com"


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PostPosted: Tue Nov 07, 2006 7:59 pm 
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whiteline lists the new alignment specs for their tuning concept and based on their bushing sets. at 1/8" (3.175mm) your rear toe is greater than the whiteline spec of 2mm and that would make your car a bit more "twitchy." try backing that off to 2mm.

if you're using the rear toe bars like LTLSU's you should be able to hold the rear toe setting pretty well. if you're using the oem flat stamped control rods don't even bother trying to dial in the rear toe. the flat control rods flex so bad that they won't hold the toe setting in a corner.

my car never got up on it's toes before i swapped to the increased caster and rear toe. now i can feel it shift it's rear line in a turn. my only complaint is the loss of low speed steering ability. it's a screamin' bitch trying to parallel park now.

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1991 Blue Geo Metro Convertible highly modified 1.0L Turbo3 5 spd. - 1991 Red Geo Metro Convertible customized with a Twincam 5 spd.

My Turbo3 Project
My Cardomain Page -Ol' Blue
My YouTube Channel
My Photo Gallery
SAAB Sonett II


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PostPosted: Tue Nov 07, 2006 9:34 pm 
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Location: orlando, fl
Hey guys,
I actually run toe in...I think T3 that you are thinking I'm running toe out? I know toe out in the rear will make it more twitchy...I tried it on track and it was undriveable, the rear end would sway back and forth, it was horrible...

I guess I could run zero toe...I assumed that a slight toe in would help with stability at higher speeds...No? What do you guys think?

T3, I am running the stock arms in the rear, as I believe the rules dictate in my class. I can change bushings, but not suspension pieces.

My suspension is pretty stiff, with 350lb front springs and 650lb rear...I run a stock rear swaybar, and no front swaybar. The balance seems decent, if not the total grip...I cannot seem to pull competitive g-forces in the corners as compared to some other race cars.

I run about 1 degree camber in the rear (all I could get), and about 1.75 in the front. I havent bought a pyrometer yet, so dont know how well this is working.

Well, this is something I can live with...I would like it to be a little less twitchy at speed, but if that is how it is, then so be it...I imagine I will learn to deal with it.


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PostPosted: Tue Nov 07, 2006 11:06 pm 
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yep, rear toe in at 1/8" is almost twice what whiteline specs for their poly bushings and +1.6mm positive caster set. the whiteline spec for rear toe in is 2mm.

as i understand how the rear toe works is that with the thrust line set up with a slight rear toe in, when the car is moving straight ahead, the rear tires scuff along slightly. when the chassis goes into a corner the outside rear tire adopts a line which dictates the new thrust line while the inside rear tire scuffs along with it's traction setting an opposing vector to the thrust line. basically, the rear end tends to hang out a little more while your "seat of the pants" senses the new and changed thrust line. a little bit more lock on the steering will change the thrust line and make the rear end hang out a little bit more.

before i installed the plus caster bushings and tweaked the rear toe in from zero to 2mm with control rods that didn't flex, i couldn't coax the rear end out of line at all. i could jack the e-brake on full and toss the steering wheel hard without moving the back end off it's thrust line. when the inside rear wheel would lift, the brake would lock up hard. when the tire came back down it'd just smoke and the car still wouldn't rotate.

you might try dialing out half of the rear toe you have. like i said, the whiteline spec says 2mm. in your place, i'd read the rules over to find a loop hole. weld gussets onto the stock control rods and replace the dead rubber bushings with solid ones. having looked at the factory control rods and having seen how they fold up when a rear tire bites the curb, they can't possibly hold the rear knuckles to spec under competition use.

_________________
1991 Blue Geo Metro Convertible highly modified 1.0L Turbo3 5 spd. - 1991 Red Geo Metro Convertible customized with a Twincam 5 spd.

My Turbo3 Project
My Cardomain Page -Ol' Blue
My YouTube Channel
My Photo Gallery
SAAB Sonett II


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PostPosted: Wed Nov 08, 2006 9:16 am 
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Location: orlando, fl
Yes, I will look into decreasing the rear toe to 2mm.
I will also look into finding some better poly bushings for the rear arms. I will talk with some other racers about modifying the rear arms.

Plan to make the move to production soon, so that class may allow more to the rear arms.

I have a welded diff, and getting the rear end out is pretty easy...pitch it into the corner, rear steps out and sets, and gun it!

I dont know if any of this will help my problems in a straight line though...we will see...
I'm checking the alignment tonight, as I leave early in the morning for road atlanta.


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PostPosted: Wed Nov 08, 2006 9:33 am 
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Location: Winnipeg
You should be making some tools to measure your "bump steer".
It sounds like you could have the wheels turning as the suspension travels downward (bump). You might be able to do a quick check by placing something along the outside of your front wheels, on both sides, and watching for movement (steering) while you have some friends jounce the front of your car. Have the hood up, and have one guy push on each strut tower while watching the front wheel movement against your refrence object.
I hope i've explained this well. If you find no noticable bump steer, then start searching for areas of the chassis, or suspension that could be flexing too much.
Darcy


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PostPosted: Wed Nov 08, 2006 10:54 am 
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Location: orlando, fl
ah, yes, bump steer...
I forgot about that one.
I'll investigate and let ya know,
thanks guys,
matt


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PostPosted: Wed Nov 08, 2006 12:53 pm 
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I had a friend who's gt had been totalled & rebuilt, poly bushings, braces, the whole nine yards, and it would do a similar un-nerving twitch on right hand turns. I'm not sure if he ever tracked it down, but you may want to look for signs of body damage (or hidden repaired body damage) near the front suspension as well.

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PostPosted: Wed Nov 08, 2006 4:08 pm 
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My car severly pulls to the left under very hard braking conditions. It seems more pronounced the wider the front tires are. It may not be helping that I did not get an alignment yet when I installed new struts in the front (with the coilover combo). I am curious to see what a solution for this would be. I thought somewhere on TS, somebody had mentioned that it was partially due to the chassis flexing/a-arms moving under the severe stress of braking, and that a lower chassis brace helped alot. IF, I remember correctly ;)

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PostPosted: Wed Nov 08, 2006 6:00 pm 
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Location: orlando, fl
yes Hightemp, I also think getting all of the front suspension tied in correctly will make a big difference...as the front suspension is pretty much the most important part of the car. Murr has a custom sized lower brace coming for me.

I also noticed that it got worse when I went to the 225/50-14's. In fact the whole car got a lot more twitchy at high speed when going to these bigger tires.

I will be going back to a 205 or 195 when these wear out, as I dont think the car handles as well (although I havent invested in data acquisition yet to know for sure :wink: )

The car hasnt been in an accident so far as I can tell, and I've been over most every inch of it.

I do run 1/2 inch spacers on the wheels front and rear to compensate for the beefy tires (otherwise they rub on the inside, against the unibody). I wonder if this has something to do with it?


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PostPosted: Thu Nov 09, 2006 8:00 am 
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t3 ragtop wrote:
i'd read the rules over to find a loop hole. weld gussets onto the stock control rods and replace the dead rubber bushings with solid ones. having looked at the factory control rods and having seen how they fold up when a rear tire bites the curb, they can't possibly hold the rear knuckles to spec under competition use.


They can and do work under competition use, but (obviously) are not optimal. The rules are quite plain in improved touring... only the bushing material may be changed. You cannot add or remove material.

Matt, what rear dampers are you using? What are the rebound settings adjusted to? If they are adjustable, definately try "dialing back" the rebound damping...

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1989 Suzuki Swift GTi - ITB Racecar
2000 Subaru Impreza 2.5 RS - Daily Driver
2004 Dodge Ram Pickup - Tow Vehicle
2006 Suzuki DR-Z400SM - SuperMoto
2009 Cannondale Rize
I rarely visit TeamSwift anymore, so please email me if you have a question. On average I'm only checking my PM's here once a month. "roy (at) forcefed4 (dot) com"


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PostPosted: Thu Nov 09, 2006 9:53 am 
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Location: Winnipeg
Ahhh, the tires! Now we are getting somewhere! When you install wider tires, or space your tires further outboard, it can have a bad effect.
On your front suspension, the lower balljoint is the steering pivot point.
The perfect spot for a pivot point is in the center of the tire (laterally)
For many reasons, it's usually not possible for cars to be disigned this way. (except many open wheel race cars) So the factory makes are car with the tire offset to the outside of the lower balljoint. Offset to the outside makes the car self-steer from braking and acceleration forces between the ground and tire. The forces are centered on the tire for the most part, but the major part of the force is transfered thru the lower ball joint. With tires offset a long way from the balljoint, even a small unevenness is braking force between front wheels will make is self-steer under braking. Solution you ask? If you can't move your wheels inboard...and you can't move your lower balljoint pivot outboard, then do what you can to make the braking force on the front wheels perfectly even. Cut the rotors, being sure to get the same surface finish on both. Replace the brake pads with new good quality pads. Next, take your calipers apart, clean them, and re-assemble with brake fluid on all sides of the square type seal. The last part is very important too. Once both sides are just freshly assembled, go for a quick test ride, then let your car sit overnight with something depressing the brake pedal to apply the brakes. This setting overnight will allow the freshly lubed seals to "find home", so that both caliper pistons will equally pull away from the rotors.
Ohhh, i forgot to mention that the caliper mounts must be clean, and lubed too, so the caliper is nice and free to lateral movement.
Happy braking!
Darcy


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PostPosted: Fri Nov 10, 2006 11:43 am 
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Location: orlando, fl
Yes Roy,
I have thought about making adjustments to the shocks...it's just that it is so damn diffcult to do. I will eventually get the externally adjustable ones, when I run into some money...
But pulling the shocks so I can push and turn...it is a pain in the ass, and I dont know if I am tuning backwards or not.

Mr pipe, I believe you are referring to scrub radius. I agree that it is now thrown completely out of whack here, and is probably the reason for the twitchyness I am feeling in the car.
I really have to work to keep the car on the track, constantly making adjustments with the wheel.


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PostPosted: Fri Nov 10, 2006 11:57 am 
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Back from Road Atlanta!
I was just there for the test day.

It had been a year since I have last driven my car...and I have never been to road atlanta before.
This is a fast, flowing, track with some exciting elevation changes. Very cool.
But, despite being a virgin there, and a little rusty behind the wheel...I had some great battles! :thumbsup:

I also got some surprisingly good video from this little crapy panasonic camera I have had for like 5 years. I will post it up in the track talk section when I go to best buy and purchase the right cord to hook to my computer.

I also realized one thing out there on track. The car apparently doesnt really pull as bad as I remembered on braking.
My biggest complaint with the handling has to be the fact that there isnt much feel through the steering... I cant tell what the front tires are doing as well as I would like.
The car is also still very twitchy at speed...this is the same as I remember.

There is one place on the track where you can track out to the curbing..and the curbing is kind of extended, so you can drive way over onto it, making more room for track out on the exit of this corner. I would hit this and as I'm going along over this extended curbing, the car is all over the place.

Anyways, sorry for the long post...I'm still riding high from the test day.

I will post up the video today or tomorrow. Lots of Honda preludes, Volks Golfs, a pinto, and dodge omni, and a couple of honda civic's....and a shitload of spec miata's. I think you guys will like the video! :P


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PostPosted: Mon Nov 13, 2006 9:32 pm 
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SCCA wrote:
At the track, I'm cruising along at close to top speed...Corner is coming up...
I brake, very hard, for the corner...
The car shifts to the left! :shock:



Kind of like...... THIS:

http://csl.forcefed4.com/roydean/ps03spin.wmv
http://csl.forcefed4.com/roydean/virspin.wmv

_________________
1989 Suzuki Swift GTi - ITB Racecar
2000 Subaru Impreza 2.5 RS - Daily Driver
2004 Dodge Ram Pickup - Tow Vehicle
2006 Suzuki DR-Z400SM - SuperMoto
2009 Cannondale Rize
I rarely visit TeamSwift anymore, so please email me if you have a question. On average I'm only checking my PM's here once a month. "roy (at) forcefed4 (dot) com"


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PostPosted: Mon Nov 13, 2006 9:44 pm 
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Wow Roy, I had to watch carefully, but I am pretty sure I could see where you are trying to keep the car straight under braking. Its exactly the same thing that happens to me.

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HiTemp Inc. ....... taking over the world one Sprint Turbo and Swift GTi at a time.

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PostPosted: Tue Nov 14, 2006 12:20 am 
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When you set front toe, are the tie rod lengths the same? This is easier to measure with tires off, and pull the front boots back on the steering rack. I always see guys adjusting one side of the rack to get there specific toe. If this happens then you are creating a bump steer issue.

THe front lower bar will help out ALOT for this. My race swift you can get on the brakes as hard as you want and it justs slows down.

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PostPosted: Tue Nov 14, 2006 3:16 am 
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Murr wrote:
When you set front toe, are the tie rod lengths the same? This is easier to measure with tires off, and pull the front boots back on the steering rack. I always see guys adjusting one side of the rack to get there specific toe. If this happens then you are creating a bump steer issue.


:goodpost:


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PostPosted: Fri Feb 25, 2011 11:01 am 
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Guys,

Have you all checked your brakes to make sure the bias between left and right is properly balanced? I've read that one of you has new brake discs installed....remember there's a bit of a break in with new pads as the discs have a coating of material that will cut away at the rotors initially and allow the disc to bed properly on the rotors...which is why most versed in suspension tuning will tell you to never refresh your rotors and install new pads at the same time.

That said, have you checked your brake lines for swells etc? These little things may be the cause, before starting to worry about steering and wheel alignment.

Cheers.

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