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Author Topic:   help on set up 4link three wheeling problem
juni
Dirt Maniac

Total posts: 184
posted April 15, 2005 11:31 AM  
I'm helping a buddy on his mod it has a chevelle stub with a 4 link . The car is fast but is carring the left front wheel about 12 to 13" most of the way around the track. Here is what he has for springs and shocks. LF-650 /75 RF-750/62
LR-165to 450 variable rate spring
RR-165to 450 variable rate spring
pull bar 38" long 36" off mid plate
10" up from rear end center line 13
degrees down hill.1050 spring,9010
shock down at 5 degees,pinion angle
at 10 degrees. LR upper link 21
degrees up hill ,L.lower link 12
degrees up hill,RR upper14degrees
up hill RR. lower 8 degrees down,
panhard bar 16" long 22 degrees
down hill to pinion (top bolt)
53% inside 52% cross 59 rear 120
split. Any help would be welcome.
1/4 mile dirt track med banks .

rpm20
Dirt Freak

Total posts: 338
posted April 15, 2005 12:10 PM  
i am no expert but i would say to get that cross below 50 and decrease lr bite some.

dirtee1
Dirt Full Roller

Total posts: 28
posted April 15, 2005 03:40 PM  
the left lower bar seems to have too much angle, we have always ran it level to 5 degrees up! The panhard bar also seems to have a little much angle also! Another thing to try would be take your split down to 50#. Never ran the varible rate springs just ran 200# both sides.

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 15, 2005 04:21 PM  
Your running progressive springs on both rears?
Any else ever run those?

fastow
Dirt Maniac

Total posts: 168
posted April 15, 2005 08:45 PM  
Juni if thats the car I am thinking of loosening it up on entry would be my guess. My opinion would be less cross to start with maybe try conventional springs anything to get it closer to 4 wheels. If you do try different springs I might be interested in them old ones lol

spde
Dirt Freak

Total posts: 243
posted April 16, 2005 02:07 AM  
The only way I know to get ride of 3 wheel is less bite in the car. Take it off the left or more spring on the right rear. I would put a 225# conv. spring on the right and go from there. pan hard and 4 link angles don't make a car 3 wheel. soft right rear springs do.If you go with a heavier rr then you might have to change shocks after that, it needs to transfer the weight faster. gl ltr

dirtee1
Dirt Full Roller

Total posts: 28
posted April 16, 2005 08:18 AM  
spde,

Actually four bar link angles on the left rear do make a car hike the left front up, as does panhard bar angle and rf spring rate.

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 16, 2005 03:03 PM  
How does RF spring rate make a car 3-wheel?

andykmod
Dirt Freak

Total posts: 351
posted April 16, 2005 06:33 PM  
If the rf is to stiff it will transfer more weight onto the rr (the car will teeder-totter on the rf and lr) Hope's this helps. I would soften rf and stiffen rr alittle also if forward bite is good, maybe take some bar angle out of the four-bar.

GRTWallbanger
Dirt Maniac

Total posts: 196
posted April 16, 2005 08:00 PM  
So your saying a stiffer RF spring will make a car 3-wheel more than a softer RF?

donslink1
Dirt Freak

Total posts: 318
posted April 17, 2005 01:02 AM  
yes it holds dynamic wedge in the car.

Mastersbilt05
Dirt Roller

Total posts: 21
posted April 17, 2005 01:26 PM  
You say that the car is fast then dont change anything. That is what I would do unless it is hard to drive. If you do want to change something then take some angle out of that lr lower link that is a heck of alot of angle. By the way that I see that your car is setup you are running solely off the left rear. You have no bite in the right rear and all the bite and rollstear in the lr. That panhard bar is at too much of an angle. Sometimes when you feel fast you really arent. That pinion angle is a little more than I would like to run also.

spde
Dirt Freak

Total posts: 243
posted April 17, 2005 09:05 PM  
Just because the 4 bar is up and you run alot of angle on the panhard doesn't mean the car will hike. I run my 4 bar on the top hole, I have a short straight bar on the bottom hole under the pinion, with 25 deg angle. My car doesn't 3 wheel. The right rear spring controls how much roll (on the gas) the car gets. Panhards set the car in the corner with side bite. RF set the car in the corner, NOT off the corner. If you increase the rr the car will not 3 wheel. I you want put a 100# spring in the RR and don't change anything else I bet you 3 wheel. GL ltr

[This message has been edited by spde (edited April 17, 2005).]

Mastersbilt05
Dirt Roller

Total posts: 21
posted April 20, 2005 11:01 PM  
I disagree with spde the panhard bar is what handles the roll. When you get all of those drastic angles then it makes drastic things happen. Just because your car doesn't 3 wheel doesnt mean its not doing because of what you said. There are a whole lot of different factors that determine many many things. Everything works together. The right rear spring doesnt necessarily mean why a car is 3 wheeling. That is what people may think until you understand about 4 links. Read a Mastersbilt late model setup sheet for a 4 link. 200 lb spring when tacky 225 when slick (RR). How much rollsteer and birdcage indexing make a heck of alot more difference then just sticking a spring in there and calling it done. When you have the panhard angle and the left 4 link angle so high and it steers forward underneath the car it cant do hardly anything but raise the left front a little bit. All this is from experience and testing. One thing that might be different is that some things may feel or drive different for different people.

michmodified
Dirt Newbie

Total posts: 1
posted April 21, 2005 06:56 AM  
If your left front is lifting, decrease sidebite by:
A) raising the j - bar
B) softening left front spring
C) increasing left side weight

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted April 21, 2005 08:55 AM  
juni,
With that much LR bar angle and that much panhard angle it will be hard not to carry the left front. I would take some LR lower bar angle out, and go to about 3-4" split in the heims on the panhard bar. Also I would pull pinion angle back up to about 8*. I would put a straight rate spring in the back prob something liek 225LR and 200 or 225RR.

I will somewhat agree with both Masterbilt05 and SPDE.

I agree with SPDE that the RR spring will somewhat control lifting the LF on acceleraion simply because it keeps the car from rocking back to that corner. But like Masterbilt 05 said you can have a car with a stiff RR spring the still lifts the left front. WE had a car last year that the RR spring wasnt very effective and on the gas it would rock back and the LF would get jacked in the air. Fixed the alignment of the spring and suddently the LF was under control. But with all the bar angle on the LR it is going to lift that side of the car, no matter what. The lifting effect on the left side is due almost entirely to the bar angle. Whether it lifts the LF tire to 3 wheel depends on several other things as well.

I think the reason Mastersbilt goes to a stiffer RR spring on dry slick is to tighten the car up and help it stick the rear on entry, and even then it will still lift the left side, maybe not jack the LF in the air but still it is lifting.

nvracer
Dirt Maniac

Total posts: 127
posted April 21, 2005 09:13 AM  
MitchMod: Softening the LF spring will not keep it from 3 wheeling. If its off the ground the spring isn't doing anything.
If you are looking to stop the 3 wheeling.
Stiffer RR spring
Raise Roll Center (J-Bar, Panhard Bar)
Reduce LR bar angles.

spde
Dirt Freak

Total posts: 243
posted April 21, 2005 08:37 PM  
I don't think you can compare a late model setup to a mod setup. The cars are to different. If you think I'm wrong, why did IMCA go to a 19" panhard this year? They were trying to stop 3 wheeling and put Pierce and Skyrockets out of the picture. If you go in the garage and jack up the car at the LR, don't lift the tire, just get the car to roll over, turn the wheels to the right (like counter stearing thru the corner), this will give you the idea what happens going in and thru the middle. I know there are more factors at work but its an idea. The car pivots to the RF And LF. Now when you get in the gas, the car rolls back, if you have high 4 bar angles, the car pivots on the RF and LR. The softer the RR, the more roll the RR gets. Its the only way the car works. Going into the corner and off are 2 seperate items. If I'm wrong then what you guys are saying is when the car goes into the corner, OFF THE GAS, the LF will hike as soon as the car rolls over. I'm no rocket sceincist but I don't think it works that way. I could be wrong. GL ltr

Mastersbilt05
Dirt Roller

Total posts: 21
posted April 21, 2005 11:38 PM  
Thank you dirtbuster that is what I was kinda trying to say. I will not totally disagree that the rr doesnt have ANYTHING to do with the lf lifting. But a 4 link is a 4 link we not only have a mastersbilt late model but we also have two dirtworks 4 links in which every adjustment on either cars fix the same problem. Just because you jack the left rear up and it doesnt lift the tire doesnt mean that it wont on the track. You have to take into consideration that the rearend is torquing up and inertia is taking over too. You dont have downforce put into the right side either. If you want to experiment put a 300 spring in the right rear and see what happens. We run a 400 lb spring in the rr of our Rayburn which is a lighter car and it is on the z link and on the birdcage. Like dirtbuster and I said, the lr bar angles are at fault the most, and yes IMCA did go to a longer panhard bar to solve the 3wheeling problem. That is one of my other points the shorter the panhard bar, or any bar, the quicker and bigger the reaction of it. Juni has a 16" panhard with a steep angle. When the car rolls over everything on the center to left side of the rear end is at so steep of an angle that the car really has no option but to pick the lf up. Off the gas is the same effect sort of that it is in the shop (No rear end torquing, etc) I understand that its rolling but its not "Driving" up under like it would on the gas. Thats just the way I look at it.

[This message has been edited by Mastersbilt05 (edited April 21, 2005).]

dirtbuster
Dirt Forum Champ
Total posts: 2007
posted April 24, 2005 09:05 PM  
SPDE

What I am saying is that under acceleration the driving force of the axle on the bars on the LR is what creates the lift. Not the bar angle itself. As you enter the corner and the car rolls over you are increasing the angles on the LR and panhard but until you start into the gas and drive forward there is not lifting force on the bars. Once on the gas then its a combination of bar angles and springs that determines whether or not the LF gets jacked in the air.

IMCA should have looked into the panahrd rule furthur before going to a 19" minimum. Using a long panhard bar to the right side of the axle will pin the RR harder and still get the car to 3 wheel. I have seen several cars at our laocal tracks with a long bar that look exactly the same as our short bars on the track.

jason lee
Dirt Roller

Total posts: 10
posted April 25, 2005 03:14 PM  
one thing you can do before making a ton of changes is just to put more downward angle in you right rear bar that goes to the back of the car , try that first and see what happens ,,,,,

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