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Author Topic:   Lower Link Angles (2-link susp)
BrianW
Member
posted July 23, 2003 01:35 PM
Wondering what impact the angle has on handling...

Some Backround: I'm fighting a mid-turn to exit loose condition on my "new to me" Mod. The car is really fast into the corner and I can go harder/deeper into the corner than a lot of folks, but once in it gets loose... The oversteer condition is especially bad in dry-slick conditions. This car was supposed to be set up already so I assumed only minor tweaking would be needed as I learned to drive this class, but after some basic changes I decided to start from the very beginning. I measured the angles on the lower links of the 2/3-link suspension and they were set at nearly 0. Also the pull bar was at 5* downhill. I've moved the pullbar down to 15*. The lower links are level or at 0*, and the basic setup guide says to start at 5* uphill. Will moving the links to the 5* uphill position change handling dramatically mid-turn on out?

[This message has been edited by BrianW (edited July 23, 2003).]

speedy79
Member
posted July 23, 2003 02:05 PM
Or maybe when you have your push and you have the wheels turned when they finally hook up it throws you into a loose condition??


BrianW
Member
posted July 23, 2003 04:35 PM
How about this explanation - the rear end wants to come around once I get to mid-turn - then it just wants to slide on out and around... Stagger is about 1" on the rear (IMCA tires).

The scale numbers are right on from the chassis setup sheet that I've got so I'm thinking it's either basic suspension geometry or spring reates (running recommended springs). I've also bought an infrared pyrometer for this weekend so I'll be taking tire temps in hope that will help diagnose the problem.

Racer14K
Member
posted July 23, 2003 06:01 PM
I was always afraid to make changes to my car because I didn't know how the car would react to the changes. This is what I did to my two link this year and it made a world of difference.
I put the the pullbar at 20*, changed to a short left trailing arm (10" tube), long trailing arm on right, run both arms in the top holes at the frame, put on a short panhard bar. I have the same driving style as you but I run it up on the cushion next to the outside wall. If you're running low to middle when it's slick you may have to play around with right trailing arm angle to suit your needs. When it's slick I try to run as close to 0 stagger as I can.
I am thinking about trying a short trailing arm on the right but I really like the way it handles with the long one.
225lr spring front of housing and 150rr spring behind housing.


hiway80
Member
posted July 23, 2003 07:41 PM
Thanks for all the input - The basic setup that I've got from the steve smith book is both arms 5* uphill - I may try moving the RT side up one hole and see how it goes since they're both level the way that it sits now.


CUSTOMPERFORMANCE
Member
posted July 23, 2003 09:23 PM
I run my left rear at 20 deg uphill and the rr flat and love it on dry and tacky tracks. On tacky it tends to lift leftside too much so i may back the lr down to 10-15 deg angle and put the r up to 5 deg uphill. I run long lower links on both sides with a short j bar.


CUSTOMPERFORMANCE
Member
posted July 23, 2003 09:25 PM
i also run the pull bar at 15 deg angle and mounted clear to the left of drive shaft.


dluna
Member
posted July 23, 2003 10:38 PM
Brian,

First thing first...do you understand the concept of rear steer and what happens w/ the bar angles when the chassis rolls over? For instance, do you understand why CUSTOMPERFORMANCE would raise the R side arm up a few degrees on a tacky track?

Chad
Member
posted July 24, 2003 01:19 PM
One thing to consider that hasn't been mentioned, especially since it sounds like you purchased the car and have been running the set up that came on the car: check the rear end alignment and make sure the right side wheel base isn't longer than the left. You can check this a number of ways, but the surest and simplest method is to drop a plumb bob from the lower ball joints and the rear end housing. Lay a piece of metal across both points in the front and again in the rear. Measure from the front to the rear and see what you've got. Try to mearsure back about where the tires would be. Whatever you do, always do it the same way each time. Make sure you measure back at 90 degrees to the metal laying across the plumb bob marks. This will tell if you rear end has any "lead" in it. If the right side wheel base is longer than the left, adjust the links so the wheelbase is equal on both sides. If you want the car a little tighter, you can adjust by either lengthening the left or shortening the right-this will add lead. Many say running lead is a bandaid for something else. I personally found that I preferred to run the rearend square and adjust the suspension for changing conditions. Don't be afraid to move those links. You need to try drastic changes (at least 5-10 degrees) in the angles to tell if you're moving in the right direction. Hope this helps.


BrianW
Member
posted July 24, 2003 04:26 PM
quote:
Originally posted by dluna:
Brian,
First thing first...do you understand the concept of rear steer and what happens w/ the bar angles when the chassis rolls over? For instance, do you understand why CUSTOMPERFORMANCE would raise the R side arm up a few degrees on a tacky track?

I don't fully understand why one has the RR up and the other has the LR up - I do know that as the bar travels up closer to level it gets "longer" and the further from level it gets shorter - so with the R up on a tacky track as the car rolls in the corner the R side will get effectively longer and the left will get shorter as the chassis rolls - that will **** the rear and make the rear want to go "right" pointing the nose into the turn... I guess once there is enough traction it would allow you to "drive" more around the corner VS slide??

With that said I don't understand why CUSTOMPERFORMANCE and hiway80 are excatly opposite....



hiway80
Member
posted July 24, 2003 04:42 PM
quote:
Originally posted by hiway80:
for nearly a year, I was fighting the car loose coming out of the corner....<<SNIP>>
I think you'll like it after you move the rr trailing arm up a hole, try two if that don't work.

If I get to the track early tonight I'll be moving the RR link up a hole - we'll see how your advice goes


dluna
Member
posted July 25, 2003 01:42 PM
Brian,

CUSTOMPERFORMANCE builds his own chassis and I hear they do really well. SO, with that being said, I would bet that what he is saying is pretty standard for a 2 link car. I am not, however, downplaying any of hiway80's comments!!! Although I can not picture how moving the RR arm up would help tighten up a car. Perhaps that is just the setup that works best w/ his car?!?

If I were you, I would put more angle in that LR arm. Run it about 10 to 15 degrees and the RR arm 0 to 5 degress. You will get much more forward bite if you increase your LR angle. Like CUSTOM said, if the track is dry, set the RR arm at 0 degrees so it will tighten up the car. Remember...if the right side wheelbase is shorter than the left, it will tighten up the car, and the opposite if the right is longer than the left. So when the car rolls over and the ride height angle of the arm was 0 degrees, the right side wheelbase will get shorter.

One of the MAIN things you need to consider though when moving bars up and down is the wheelbase. If you make the changes at the track, just measure from wheel to wheel on ach side to get a "close" estimate of the wheelbase. This will not be exact, but fairly close if you do it right.

GOOD LUCK!!! and let us know how it went.

BrianW
Member
posted July 25, 2003 04:00 PM
So.... Sounds like I might be better off doing this from home when I can square up the rear end again after adjustment...

Thanks for all the help so far!

- Brian

hiway80
Member
posted July 27, 2003 12:34 PM
OK!! I think I'm starting to understand...

Putting the LR up at a higher angle will shorten that side up "faster" as the body lifts on the left side and then angles the rear letting the car "drive" around the corner when it gets slick VS a slide??? Sound about right guys??

TOOLBOY
Member
posted July 29, 2003 07:16 PM
Toolboy, Using your brakes in the corner with the throttle still on is no band aid.Many fast guys do this.If it works use it.If you are fighting a push coming off the corner and your brakes are adjusted properly (right front shut off and bias towards the rear)it will suck the car down in the corner for a good shot down the straight. Panhard position has a lot to do with forward bite.We fought an exit push and started moving the rr trailing arm up.It gave us more roll stear and forward bite at the same time. our main event setup is 20 degrees left on 16 c to c.10* rr on 21 inch c to c. Panhard is 20 inchs ,mid axle height on frame and bottom axle tube rear.We also run three inchs of stagger (hoosiers).If it is real dry slick any car will buzz the tires.I have used the brakes down the straight to stop wheel spin.This is the best traction control known and can never be detected.There is no such thing as a crutch in racing.Only to narrow minded people.

[This message has been edited by wissota3x (edited July 30, 2003).]

TOOLBOY
Member
posted July 30, 2003 08:57 PM
thanks 3x i am new to modifieds and need to learn how to drive them. i have been holding off on changing things until i feel comfortable in the car but at this rate i dont think i will get there until i start moving things. i havent moved the panhard bar yet. we run a j-bar. i think i will move the rr lower link up one hole and move my torque link down one hole and see what happens this weekend. i will try this for a couple weeks to get a feel for it and then if that doesnt fix my problems i will try moving the panhard bar. thanks again. we are open to all suggestions and ideas. i know the first year is a learning year but we just dont seem to be making progress.


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