Badazzchevy327

i was wondering if any of you suspension guys off hand know what spring rate i should run in the rear. i have the truck in sig, it weighs in at 3390 as of now. and has ladderbars with qa1's. current springs are unknown but are way to stiff, no weight transfer. any help is apreciated

senor honda

Coils or leaves?
What is the stock spring rate?-Bob

Badazzchevy327

here is a picture of it. and i have no clue what the stock spring rate is on the leafsprings.

DANGERANGER

Figure what the weight balance is then call A.R.T. ask for Tony he'll hook u up.

Badazzchevy327

ya im gonna be throwing it on 4 digital scale set up soon. was just seeing if anyone knew off hand or knew where to start. the more info the better... but now that im fixing to start spraying off the line im gonna have to lift the truck up cause it seems the frame would hit the axle with how much its gonna sqaut soon

senor honda

It looks like you have coil springs over the shocks (coilovers), and a panhard bar
to locate the axle side-to-side. The best source for drag suspension tuning might be Automotive Engineering in Largo. They have about 40+ years of experience, and can probably tell you what coil springs to swap over to..... The truck has no leaf springs.

There is a multitude of adjustments to be made on a drag car.
Serious racers would have several sets of coils and change them based on track conditions with heavier springs on right side to control axle-frame twisting off the line. There are also several suspension and axle-locating designs that people say work for them, and some people say that ladderbar/panhard rods
can be made adjustable and improved on, but I would start with advice from
Automotive Engineering......

To get weight transfer and bite off the line for drag racing requires a different setup than for road racing. While I have devices to measure what a FWD import suspension does off the line, and can set the front end accordingly, Road racing, left/right turns, and stock car racing are what I am better at.-Bob

treekiller

no one can answer this question without knowing the balance and suspension motion ratios. best to find the rate and work backwards.

Spring tuning is a black art. while the numericly perfect spring might be like riding a jackhammer. and Shock tuning has more to do with ride quality then does the springs rate. a good shock can dampen a very aggressive spring rate if need be. best thing to do is find the spring rate before making ANY changes.. look for printing on the spring a part number to refrence a QA-1 catalog. (silver springs are Qa-1 brand)

if that does not work then use this method
Calculator for Finding Spring Rates from Design Specifications for Compression Springs

if that is still out of the realm of possibility you can get out the handy dial calipers and measure the wire diameter of the spring and use this

F650 Spring Rate Claculator FAQ

while not the most accurate method it will get you close.

once you've found the spring rate make a single decisive change you will not feel anything less then 50lb/in but remember a low spring rate will cause you to loose some carrying capacity if you use the truck for hauling.

while springs are cheap I would FIRST try to adjust the shocks if they are adjustable.

senor honda

A thought crosses my mind that maybe you should hook up the spray before changing spring rates. With more power, it's possible that
your current springs might just turn out to be about right, and you don't want to swap springs first, then find out that you need to buy more springs and swap them all over again.

You might run a diagonal brace from near the right rear of the ladder bar to the left front of the opposite ladder bar and eliminate the panhard bar.
As the panhard bar's end rises and falls under acceleration, it will arc, and move the axle slightly side to side. The diagonal brace will not shift the axle side to side.

Use rod ends the same size as the ladder bar's rod ends and longer graded bolts. I would also put a capture washer on all rod ends so that you don't lose a suspension bar in case a rod end pulls out.

And instead of guessing, calculating, etc.,...... if you want those springs checked to see what the spring rate *actually* is, get back to me. -Bob

Badazzchevy327

damn guys thanks for all the info. i got with some locals and we found a lot wrong with my set up including the placement of the suspension. everything so far is looking very positive.

btw it is strictly for race/driving, most hauling is two people.

and ya im dropping the panhard for a track bar, i think thats what they call it, it slips my mind right now.

badhombre

how long are the ladder bars? I had a similar problem when I built my s-10. I made my ladder bars too short, so it would hook good until just before the 60' mark then the bars would actually beging to lift the rear of the truck instead of pulling the weight back onto them. from looking at yours, the upper link mount looks awefully close to the centerline of the axle, I would think it should be up a little higher. also what is the pinion angle at? should beabout 1-2* down at rest to allow for some reaction and slack in the suspension components. u joints are the strongest when they are straight. I would check over the suspension geometries some before swapping springs around. unless you happen to have a few just lying around, or you know someone who does so you can try some different rates and see what works best for you. also, on alot of drag only applications, they will use a slightly stiffer spring on the right rear than on the left due to the fact that once you rear end reacts, there is a twisting force down on the right rear, and a lifting force on the left rear. they offset this with the stiffer spring. thats why on a lot of cars that pull the front end, you see them twist to the left. just some things that may help you. good luck, glad to still see some people going fast the traditional way