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Author Topic:   Set-up help, Big Tri-Oval again.
Dirt Forum Champ
Total posts: 796
posted October 04, 2005 02:00 PM  
We went back to the big tri oval we race at mainly over the summer, they were off a few weeks and we had some co-operation issues with some pistons.

Anyway, first time there with the short bar. The car was fast but tight as heck. You could just pound on it in, and it would lift the LF about mid corner and pick up a throttle push out. Car wasnt bad, i just need to get rid of some side bite and maybe some left side lift or scotch.

We run outlaw tires here, so that may be some of the trouble, they got loads of grip. Plus we run Sprint car fronts on the left side, soft compounds hand me downs from a friend.

Here is the set up:

1000lb RF / 75 shock (about 4" of movement)
850lb LF / 74 shock (3 wheeled a little)
(Ford clip, kinda like a wide chevelle)

300lb RR / 93/5 shock (swing arm) (5" movement or so, 3 wheeled)
275lb LR / 97/3 shock (rocket style 4 bar)

18" swing arm RR, with a 16" rear link.

Pull bar is at 15*, down, no shock.

No brake chain / bar.

53% rear, 54% cross and 54% left side.

I'm thinking i need more rear%, and that would help get me more cross, i'm thinking 56% rear, and 55% cross will help. I am wondering if the low rear percent is causing the front to collapse to much and push in the middle?

Also i am thinking of flattening out the short bar, it has 4" rake now. Even with the pinion. If i knock the rake down to 2" and then raise it one hole on the pinion plate, will that loosen it up, side bite wise?

We like the entry, just need to loose some side bite in the middle so it comes on around a little more to clear the apex.

Any thoughts?

Dirt Full Roller

Total posts: 33
posted October 05, 2005 09:53 AM  
Here's a few things you could try...Wheelbase: most nites we are a inch longer on the right side.Stagger:haven't been under 3 inches all year.Wheel offsets:moving the left rear out will loosen a car up from the middle off.Pullrod:if you are left of the driveshaft move both ends towards the right.Panard bar:I would try moving both ends up equally,although we ran this setup a few years ago and had pretty good luck with it,the driver didn't like the short bar we was always on a 15 to 17 inch panard bar..Springs:if you can get softer on the RF it will help,we had 650's across the front in a chevelle stub and that was before we learned anything about moving roll centers around,and if it was me I would try taking LR out. Putting it in or adding rear will just make on the gas push worse,well Krom thats some of the things we have done in the last 8 yrs of ump modified racing to loosen them up hope it helps.

Dirt Forum Champ
Total posts: 874
posted October 05, 2005 09:55 AM  
I'd get your cross or LR down quite a bit. On the gas is LR, Off it is Cross.

I'd try 52 cross, and moving the LR out will tighten a car up all around.

Dirt Forum Champ
Total posts: 505
posted October 05, 2005 09:56 AM  
First off do you have the rr trailed at all?

I wouldn't add more rear, its only going to cause more of a throttle push.

If your tight mid corner like you say you need to decrease front roll resistance or increase rear.

If your getting 4" of travel on the front I would say your best choice would be to stiffen both rear springs. By doing both you won't effect transitional handling, only steady state (ie mid corner). To me 5" of movement on a swingarm is excessive. I like to see 1-2".

I've never seen this track but it sounds fast and high banked. And seeing as how you are on gumball tires don't be afraid to go stiff on your spring package. I ran as high as 500lbs on swingarms before on high bank hooked up tracks. This year in the l/m I have run no less than 500lb rears and as high as 650lb.

To me the track sounds like a perfect candidate for a rayburn style swing arm on both sides. High bank tracks don't lend themsleves well to 4-bars because the high banking reduces body roll, which 4-bar cars depend upon to turn. I would also consider going back to the j-bar or a long panhard bar behind the rearend.

A couple other thoughts to consider.

Where is your front roll center?
Is the r/f bottoming out at any time?
Depending upon when the car picks up the l/f a stiffer l/f may help mid corner.
Where do you have your top rr bar?

Dirt Forum Champ
Total posts: 796
posted October 05, 2005 12:09 PM  
The last time i calculated the front RC, it was 4" above, and 3" left of center. I have been wanting to move it around, but hadnt found the time.

Stagger was at 2" front and rear.

RF is not bottoming out, but its close.

Top RR bar is about 10* down, max adjustment.

About the Rayburn swing arm deal, there are a couple guys that run a swing set up, and there fast. I almost switched to a double swing / z link set just to try it, from what i hear its a good set up to drive straight, which would be good for this track i think.

I'll try a few of the following:

More stagger
LR offset, i got a 3", 4" & 5"
Less LR bite, 125lbs
raising the rear panhard bar, both sides.

Any other thoughts?

I appreciate the info and help, we ran the best we ran all year there last week. Car is only about .3 to .4 off the top 2 cars, so were getting it.

We had been prevously running a J-bar, and it was set where the back of it (the flat straight part) was flat, or level. That seemed better all around, maybe we'll go back to that on this track.

Appreciate the thoughts, Krom.

Dirt Forum Champ
Total posts: 796
posted October 05, 2005 12:12 PM  
Oh, the track is fast, from what i can tell the fast way around it is to get it set where you can hold the gas on all the time and just slightly roll off it in the middle of the turns, and a little in the tri-oval part.

Slightly rolling off the throttle to about 1/2 or maybe 3/4 and then back after it.

They say the track is only 15* bank, but that i believe is inaccurate. Its 15* thru the tri-oval and about 20* in the turns.

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