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Author Topic:   need help on rear end lead and rear steer
Dennis Krause
Dirt Roller

Total posts: 5
posted June 03, 2002 08:23 AM
I'm looking for some help on rear end set-up. I have a home built Z-link car new 2001.
Finally got the car handling to where I feel competive in every race, but I'm getting beat off the corners on dry slick tracks by some guys runnning four bar cars. I have a 175#rr, 200#lr on the swing arms, long pull rod at 14 degrees with a progressive spring, 48.5% cross weight with 57.5%rear. I'm currently running 3/8 leed on the left rear. Thinking on running square or right rear leed. Tried running more cross but the car was tight getting in. Any thoughts?

[This message has been edited by Dennis Krause (edited June 03, 2002).]

[This message has been edited by Dennis Krause (edited June 04, 2002).]

CUSTOMPERFORMANCE
Dirt Freak

Total posts: 464
posted June 03, 2002 08:50 AM
I would square up the rearend and run the lead in the rr not the lr 1/4-3/8. For a swing arm mounted springs your sring rates should be closer to 250-275 lbs. Run the cross closer to 50-51%. What kind of panhard bar do you have?

Dennis Krause
Dirt Roller

Total posts: 5
posted June 03, 2002 09:59 AM
customperformance, thanks for the response. When I looked at my numbers, I think your right on with the rear leed thing. Should keep the rear end from kicking out coming off, right? Maybe thats why I have to run such low cross weight to get the car to turn in the middle of the corner. More cross should help coming off too. On the panhard bar, its 23" center to center and behind the rear end. I'm 6 1/2' off the ground on the axle end, and 10" off the ground on the left frame side. Howe about the rear steer thing, do mods respond favorably to any body roll induced rear steer?

wfoondirt
Dirt Freak

Total posts: 242
posted June 03, 2002 01:07 PM
I second customs suggestions above but i would also suggest a stiffer pull-bar spring, due to the rearend being floated, most typically around 1200lbs but it depends upon how much travel your getting, and also increasing rear percentage closer to 60%. Another suggestion is like custom said the springs not only seem soft for a car with the springs mounted to the links but the stiffer spring should be in the left rear. As far as building a lot of rear steer in a car i am not a big fan due to it tends to make the car less predictable, escpecially on a rough track.

[This message has been edited by wfoondirt (edited June 03, 2002).]

awkwardjeff
Dirt Freak

Total posts: 390
posted June 04, 2002 06:03 PM
here are MY thoughts......not to take anything away from the other people that have already responded......I would get the front tires to weight the same....lets start with a 2500 pound car......58% rear.....that makes the rear weight 1450......if you run 160 pounds of bite that makes the right rear weight 655 and the left rear weight 805......following along?? then I want the left side and cross the same percentages...56% for the left and cross, that makes....525 on each front tire......

my other thought is NOT to lead either side of the rear end.....square the rear, and let the body roll steer the car into and around the cornor.....but as you coome out and the right rear shock rebounds you want the rear end going straight.........also, a 200 in the right rear?? and 175 in the left?? is that correct is seems backwards???? left rear is NORMALLY stiffer.........and for being mounted on swing arms the rates seem low for the ratio on the swing arms....this will allow the spring to compress but without enough force to plant the tires....unless the track is soooooo dry I don't understand......like a sand dune....

if the car was tight getting in after adding cross weight I would like to know how long the rear arms are and the angles......I would think the front mounts of the rear swing arms are too low not allowing enough angle to effect the chassis in the proper way.........when you added cross weight did you add left rear or right front????? both add cross......but have VERY different effects on the car.

Jeff


2nd2none
Dirt Maniac

Total posts: 193
posted June 04, 2002 06:31 PM
im curious how you can get a car to turn with 160 lbs of LR. i run about 30-40 lbs of LR and the car is throttle tight coming off on a tacky track (hotlaps and sometimes heat races) but on dry slick features its pretty skatey. i would be scared to run the LR up to 160 lbs of bite because i wouldnt think the car would turn at all. or is that 160 lbs with the driver in the car??

[This message has been edited by 2nd2none (edited June 04, 2002).]

28
Dirt Full Roller

Total posts: 36
posted June 04, 2002 09:14 PM
Jeff, you said that adding cross to the RF and LR have very different effects. Explain if you will. That is news to me.

2nd2none, We run close to 200 LR bite when it get really dry. 3 link that is. With my 4 bar I could never get that high.

[This message has been edited by 28 (edited June 04, 2002).]

2nd2none
Dirt Maniac

Total posts: 193
posted June 04, 2002 10:29 PM
my car is a long 3 link with LR behind and RR on top, have ran LR infront and on top and having it behind seemed to hook it up better, ive got 58% rear and with our hoosier tires we can only get the exact same size tire so only way to get stagger is to blow the RR up and set it in the sun before races. I still dont see how you can get that much bite in it and get it to turn but its something i might try sometime.

WPP
Dirt Maniac

Total posts: 162
posted June 04, 2002 10:34 PM
I was needing help on this subject i checked my rear steer today on my rayburn swingarm with 14in swingarms and 30 rear control arms and i come up with 1 1/2 rear steer i thought this must be wrong i did not know you could get this much i have 5 degrees in the upper control arms with the swingarm i have both in the third hole i thought running the long rear bars it would not have this much steer.This is a mod just running the long rears any help on this i would be thankful this is a new car dirt works i maybe checking this thing wrong i just need alittle help here

awkwardjeff
Dirt Freak

Total posts: 390
posted June 05, 2002 10:15 AM
everyone, The weights I gave were with driver in car........because we all weight different and seat is off-set in chassis different...........

28, You want me to explain how adding weight to the right front effects the chassis different than adding weight to the left rear, but they both add cross weight............if you add weight to the left rear, that tire will have more grip .....so as you get off the gas and in the brake it will help turn the car into the corner.......then on exit because it has more grip it will tend to drive off that tire more again..........

If you added the weight to the right front instead............it will push going into the corner......right front would have too much braking power......pulling the car to the right as you want to turn left.....unless you ran a brake shut off....but because you added weight to the right front instead of the left rear you did nothing to help the car on corner exit....there is more here that could be added, but this gives a person a good idea of what's going on

You must understand a few thing first,, You can NOT change left side weight without moving something........most common is lead weights, battery, wheel offsets.......

You can not change front/rear percentages without physically moving weight either.... the ONLY thing jack-bolts will effect is the ride heights and cross weight distribution..

If the chassis isn't built with enough left or rear percentages there is nothing to do but add weight or start moving things. I did get a message from Dennis Krause, the person who asked the original question....he has since edited the spring rates.....I posted they seemed backward.......I was correct, left rear was #200 spring and right was 175..........we have all made mistakes. I just wanted the correct information to help give a correct answer...........

Jeff

awkwardjeff
Dirt Freak

Total posts: 390
posted June 05, 2002 10:25 AM
2nd, You would have a problem running high amounts of bite in the left rear.....the reason is the long amrs and 3 link....NOT ENOUGH REAR STEER TO TURN THE CAR NATURALLY, ESPECIALLY WITHOUT STAGGER.........

I have a Z-link, over 300 pounds of bite, but run large amounts of rear steer and 3-5 inches of stagger...........A lot of cars are built this way.......and run about the same numbers..........A lot of cars are built like yours and run numbers close to what you have too.............it's all about what you understand and are willing to work with........I will say that on most nights you could be off a little on set-up and still be fairly fast. On the other hand if I'm off a little it's like being out to lunch.................it takes more knowledge and a willingness to change the car often to keep up with track conditions on a 4 link or Z-link.

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