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Author Topic:   body roll
Alltel
Dirt Maniac

Total posts: 180
posted March 21, 2005 04:06 PM  
I was just wondering about body roll on my car. All other 4-bar cars around here carry the left front all the way around the track, and mine doesn't even start to lift the left. It lifts fine on the left rear, but the right side only compresses about 1.5-2"

4-bar z-link on a big chevelle chassis.
springs 700#LF 750#RF 200#LR behind birdcage 125#RR on top of housing
93 Pro shocks on rear 753 on front.
52%left
57%rear
51%cross with 120# of LR
25" pull bar with 20*
Left upper 22* Lower 7* up
Right upper 5* down Lower 5* up
19" J-bar with in bottom pinion hole with 6" of split.

leapinlizard
Dirt Freak

Total posts: 402
posted March 21, 2005 08:23 PM  
Are you fast? Why are you worried about it?

You'll get better traction and an easier drive with four wheels on the ground rather than three. Racer's often forget the entire plan is to get all four wheels working together in unison and doing the same amount of work. When you find that balance, work on perfecting it. Lifting the left front is nothing but a crutch for a tight car. Entering enough right rear weight to cause a negative down force on the left front is NOT working all four tires. It loosens the car enough to negotiate a corner. Imagine how fast you could be if you were able to put down that much power to all four tires!

#13 mod
Dirt Full Roller

Total posts: 72
posted March 23, 2005 07:01 PM  
AMEN!!!!!!!!!! 4 on the floor........ If you look at most of the top latemodels now a days you see them with all 4 on the dirt. Must be a reason them to come back full circle.

Alltel
Dirt Maniac

Total posts: 180
posted March 24, 2005 02:49 PM  
I said nothing about wanting to 3-wheel a car. I said others did it. I want the car to gain roll. The left front frame doesn't rise at all and the right side doesn't compress. The car just hikes up on the left rear. The rest of the car stays pretty much flat. We run a very slick, flat and tight race track. I wan't the car to roll to transfer weight and gain roll-steer quicker.

BTW cars I've seen 3-wheeling in this area. Jason Hughes, Kelly Shyrock, Al Henja, John-o Whittington, Gary Clark, Howard Willis and More. Those guys are far from slow. Again I didn't say I wanted to do it, but it definately isn't the slow way around here.

[This message has been edited by Alltel (edited March 24, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted March 24, 2005 03:13 PM  
If your car is good, just needs some fine tuning go to the shocks.

Try a 3 comp & 5 rebound on the RR and 4 comp & 5 rebound on the RF. Get it layed over and it will hold.

You may also want to try switching the front springs around.

Dont do all that at once thou, it should be major loose in.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 24, 2005 03:46 PM  
where is your shock mounted on the RR?

Where do you have any ballast lead mounted?

I would think with a 125 RR on top the housing you shouldnt have any trouble yanking the LF off the ground at all on the gas. If you arent getting any roll on the front soften the RF spring to get more travel. This will also let the car roll up on the LR a little quicker pulling in roll steer at tthe same time.


Alltel
Dirt Maniac

Total posts: 180
posted March 24, 2005 08:02 PM  
My right rear shock is behind the birdcage.

No ballast, but I mounted the fuel cell and battery high and in the center of the chassis.

I had thought about softening the RF, but I thought it was pretty low as it was. I can't figure out why with a 125 spring and a 93 shock on the RR, the rear quarter doesn't drag the ground.

Only thing I could come up with is too much angle in my J-bar. I've got at least twice as much as anyone else. I was wondering if the angle is causing a high roll center and keeping the chassis from transfering the weight. Thanks for suggestions guys.

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted March 24, 2005 08:46 PM  
750 on a chevelle frame isnt that soft. we've been down to 650 before on ours. It could be that the stiff RF isnt allowing the car to roll onto the RR as much as it wants to. The other thing is that your RR spring might be so soft that it doenst plant the tire and make it stick. For instance. Last year we went from a 200 to a 225 and got more travel and driver said the car stuck better at the same time. It might be a case of being too soft onthe RR.

That doesnt sound like a an excessive amount of anlge in the jbar. i know guys that are running more than that.

your pullbar might have somethign to do with it. With a shorter bar like that and a lot of angle like that when on the throttle will tend to hold the rear of the car up, in effect the pullbar is carrying some of the weight instead of the RR. If you take some angle out of the pullbar you might see more travel on the RR as a result. We had that problem with a 2 link car, couldnt get any shock travel over 1 1/2" or so on the RR but the car was fast. New car started taking angle out of the pullbar and started getting more travel and the car rocked back on the RR instead of lifting the whole rear of the car.

[This message has been edited by dirtbuster (edited March 25, 2005).]

Kromulous
Dirt Forum Champ
Total posts: 796
posted March 25, 2005 06:13 AM  
Alot of angle in the J-bar will raise the roll center. Our 4 bar car liked it a little more flat, but i run 250 plus lbs spring on the RR.

Maybe just lower, angle wise try that, and then try lowering the entire bar straight down and see what you think.

dirtracer14
Dirt Forum Champ
Total posts: 1261
posted March 25, 2005 10:01 PM  
It allmost sounds like you have a bind in the rear..... I had the same problem 2 years ago car would not roll onto the rr and stay and when on the gas it would lift the whole rear and make the rear want to skate out. I pulled the springs out of the car and dropped the lr down and tried to lift the rr side up and it had a stiff spot right about were the travel was. After checking everything we found the panhard had a slight bind about 2" into the roll on the rr. We pulled the panhard off and no bind. I also had gone down to a 125 with no luck or roll. Once i got it fixed i couldnt run any softer than a 175 or it would bury the rr. Just somthing to look at!

Almost forgot i also leveled out the rr bars to help drive the rr down when getting on the gas.

de94wcc
Dirt Forum Racer

Total posts: 87
posted March 25, 2005 10:34 PM  
Go to the tool box and read the technical article on panhard bars. Angling a panhard bar downhill creates a lower roll center. Taking angle out will raise the roll center and only contribute to your weight transfer problem. I have to agree you may have a bind somewhere. We run a very similar setup to yours and are working to keep the left front down more. Only difference is we run the rr spring ahead on the bird cage.

Alltel
Dirt Maniac

Total posts: 180
posted March 26, 2005 12:30 PM  
Well, I could agree with the bind. I'm just wondering though. I can stand on the RR and it drops no problem. I can jack the car up and it lifts with no problem. Yesterday I jack the left front up and the right rear dropped until the frame almost hit the ground. Could it still have a bind in it, and if so, where at? What could be causing it?

dirtracer14
Dirt Forum Champ
Total posts: 1261
posted March 26, 2005 05:14 PM  
What do you have for a pullbar? Spring,rubber? My car would do the same in the shop jacking it up and so on. It was when i pulled the springs out and dropped the lr down and pulled the rr up that i felt it...it was not a huge bind just a sticky spot but on the track it would be fine on tacky ...wich had more side load force...but when the track got slick it would take a lot more to get it to roll.....Hope you understand what in tring to say...not saying that is what you have...it just sounds like it to me... With a 125 spring it should fall on the rr and not come off it. The other thing is the lr underslung notched down if so how much Were is the rr spring located? How far does the rear pull to the left when the car rolls. When the rear rolls bar on the pullbar it could be cause a bind also. What is the width of the rear and what tire offset on the rr? I know when i pull the lf it is NOT from the rr going down there are a few other things that allow the lf to come up so it may not be that they are laying the rr down?

wissota3x
Dirt Forum Racer

Total posts: 86
posted March 26, 2005 06:13 PM  
alltel,
I would say that your J bar is at alot of angle. Drop it on the frame. If you are packing ballast, raise it up.Possibly raise the fuel cell.Also no one ever thinks about front roll center. Is there alot of angle in your upper A frames? This can cause alot of problems along with engine location being to low. Not pertaining to your lack of roll but those left rear bar angles seem pretty steep by todays standards.The bottom bar should be close to flat and the upper bar in the 15* range. 250 # spring LR behind on the cage.175 on top RR. A little more LR bite with those bar angles.
Does the car skate or how does it handle ? Are you lacking side bite ?
Are you running a spring pull bar ? With all that angle that you have in the J bar, The spring bar and the J bar can possibly hit one another under accelloration.Depending on how high the spring bar is off the top of the housing. JMO

[This message has been edited by wissota3x (edited March 26, 2005).]

Alltel
Dirt Maniac

Total posts: 180
posted March 26, 2005 08:52 PM  
I took the J-bar off today and jacked the car around with no change, so I don't think it is binding. Car had a old double spring pull bar, but I changed it to an AFCO spring bar with 800# spring, but I haven't gotten to run it yet. The underslung is notched far enough that the frame can raise slightly above the rear-end housing. RR spring is on top, rear moves about an inch to the left, but that is just a guestimate. 60" rear with a 4" offset RR. The car lacks side bite in the middle of the corner. I made sure the J-bar wasn't hitting the third-link. I've already learned to keep those upper A-frames close to level, and I love bar angle. I've never seen anyone run close to the angle I had on the 3-link last year, but the track is stop and go.

I jacked the car up today, under the left rear, where the trailing arms mount to the frame, and I noticed that the whole car rose. Every corner went up. Is that right?

Thanks for everybodys help. Car isn't bad, it just lacks side bite in the middle. I was watching the other cars run, and I noticed that where I start to skate and have to back out of it, they are rolling a ton and getting back in the gas.

Kromulous
Dirt Forum Champ
Total posts: 796
posted March 28, 2005 08:01 AM  
One thing to remember, alot of angle in the pull bar promotes the loss of side bite once you get back on the throttle. So you got to watch how much angle you run when the track slicks off.

alot of pull bar angle makes the car have good forward bite, but it sheds side bite, the classic give and take. So when the tracks slicks off, lose some angle to keep the same side bite.

Try a shorty bar, make up one based upon where the rear end is position with the J-bar on it. So you can change from one to another quickly and easily. Then go out and try both to see what you like.

Your binding, maybe, set the car on stands and take the wheels off and take the shocks and sliders off and inpsect piece by peice. Cycle the suspension thru its travel and look for binds. Check all the hiems as well. You'll find it, just take your time.

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