Car unloads left rear tire

[fitzee]

Hi Tony here from Newfoundland Canada. I am here to ask a qustion about our drag car.It is a 65 chevy II with coilovers front end and coilover with ladder bars out back. The car runs 10.00 135 mph with a 1.35 60 foot. In the launch the car will unload the left rear of the car. We thought that it was dropping the right rear but after studying it more you can see the left side of the car rises.I find it strange to do this.If the car hooks hard it will turn right at the launch. I`m thinking the car is hooking harder on the right rear tire and unloading the left rear tire because of this upward motion.I was thinking of ajusting the left ladder bar to pull down on the left side to help control this. Am I on the right track or way off??

fitzee

[MaxFlow]

.If the car hooks hard it will turn right at the launch.
fitzee

Going right at launch is the Driver's side rear tire loading more than the Passenger side.

You would need to decrease this loading:

by decreasing bar angle on D/S
Decreasing spring rate on D/S
Decreasing ride height on D/S

Or increasing those on the passenger side?



Depends on wheel spin ect........

[BillyShope]

I agree with MaxFlow. A spreadsheet for the bar angle adjustment can be found on Page 19 of my site.

On the spring rates, I'm assuming he meant at the front of the car. This is described on Page 16.

(Spring rate differences at the rear aren't as effective as they are at the front. In fact, if the car does not rise or squat, they're totally ineffective.)

MaxFlow, I commend you for suggesting an asymmetric bar adjustment! I'll go on to point out that this same sort of thing can be done with a 4link. In other words, the right side instant center can be higher than the left front to prevent unloading of the right rear. (This is also covered on Page 19.)

[fitzee]

So I`m way off.This is why I ask qustions. Billyshope I have been going over your site and still a bit up in the air on the understanding of alot of it. Great info and I have it book marked. One thing I understand is our problem could be due to the front spring rates.right? Funny you say this cause we plan on changing the front springs around due to the fact that the front of the car sits lower on the right side then it do on the left side. We get alot of upward movement in the left side and very little in right side. The rearend was set up with no preload on the ladderbars and the only thing that was changed out back was we ajusted the right rear spring to have some preload. The car works good and we didn`t want to change anything cause we were up in the points(bracket racing),finshed second in our class. Anyway we have a free weekend now and I want to see if we can pick up anything in ajustments.

What I was thinking of doing for now is to swap the front springs around to see if the front end rises evenly. I`m thinking that there is more weight on the right side of the front of the car at launch then the left. Agian I ask am I on the right track??

[BillyShope]

We get alot of upward movement in the left side [front] and very little in right side[front].

This is the reaction to the driveshaft torque and is to be expected when nothing has been done to cancel driveshaft torque effects. It is NOT due to a spring rate problem. There are many ways to improve the situation, including removal of the front antisway bar, asymmetric rear suspension adjustment (as MaxFlow suggested), heavier rear antisway bar, different spring rates across the front, and a rebound limiter at the right front. (I'm not suggesting you do ALL these things. These are just different means to the same end.)

Finally, whatever you do, it should be "checked out" with wheel scales and a traction dyno, as described at my site.