Guide to Rear Shocks for Ladder Bar Drag Car (Pro Street)
@gregsdart Wow that's crazy that your car was doing that. How did you see this? Go Pro under the car?
Well the car is a 72 duster all steel 3000lbs with my big butt in it, small block making right at 500 hp at the flywheel. Its nothing too crazy. I have a 8 3/4 rear axle. I do think the shocks will be mounted on the rear of the axle because the 8 3/4 has a brace and based on mounting locations that looks like they should be there. The other thing is that the car does sit low!! I have 2" drop spindles by pst. I've been reading and still reading/learning Bickell's book regarding the neutral line and the cg and IC points and concepts. Based on his book and my understanding, I think going with a lower ic for a smaller hp car is a good thing because this will keep the tires planted and weight transfer and I do not have the horsepower to shake the tires.
Problem is this car is newly back halfed and never been down the track so no clue where to start for shocks.? :(
Buy once cry once. Get a shock that can have the valving updated. And look into motion ratios and such.
As I said above...if you have a 32 inch ladder bar, the denominator in any motion ratio equation will always be 32 inches. If the shock is mounted 9 inches behind the axle (thats a WAG because I can’t remember what the shock mount position is any more) that means the simple math is
38/32 which is a ratio of 1.1875.
What that means is the shock has to move 1.1875 inches for every inch the axle moves. Since the two parts (the shock and the axle) are effectively one piece, that means the shock has to move faster over the same distance. That’s the shock speed I’m talking about. If you can’t change the valving to control the shock speed, you can make the shock effectively...non effective.
Now do the math the other way. Put the shock 9 inches in front of the axle (all you are doing is just putting the bracket on the front of the axle and moving the top shock mount to suit).
That means the math would be 23/32 which is a ratio of .71875. That means for every inch the axle housing moves, the shock only moves .71875 inches, and you have effectively slowed the shock speed down.
Now if you do the math for a 4 link you can see that ratios are much smaller, but any IC longer than 32 inches will reduce the ratio compared to a ladder bar. If you have a 54 inch IC (this is what most people start out with...and that number is about 1/2 the wheel base of the Valiant chassis) and the shock is 9 inches behind the rear axle you would have 63/54 for a ratio of 1.116.
So...that says with a 4 link the shock speed will be slower with a 4 link and any IC longer than the standard 32 IC of a ladder bar.
I ran my 4 link at 104 inches out. That math is 113/104 for a ratio of 1.0866 and that I had issues with the Koni shocks I was using, especially when I used a 30 pound flywheel.
That’s what I’m talking about when I say shock speed. The speed that the shaft of the shock travels every time you drop the hammer. You have to be able to control that. If you can’t you fight hook problems every day.
