Front coil spring theory

[John Larkin]

OK, I've thought and thought about the whole IC, lift, pinion angle thing. I believe I understand how the rear portion of the car is supposed to be set-up (and Kevin Slaby, expect a data sheet from me soon). I am trying to figure out the optimum spring for the front end. From what I understand, the front spring's job in drag racing is to maximize the front control arm travel. The springs "push" the front end upward upon launch which causes the weight of the vehicle to be transferred to the rear of the car. But the springs must maximize the length of control arm travel to be effective, i.e. if the spring runs out of "push" at the end of it's travel, then a longer spring is necessary.

This is my question: Which spring will cause maximum control arm travel but retain ride control simultaneously? Can I use a spring that is longer (for the "push") but of the same spring rate (for the ride control)? And I would have to be conscious of coil bind as well. I don't want to do as many vendors have said and "just put some Moroso Trick Springs on it". Just because all the kids are doing it doesn't make it right.

Am I all goofed up here?

 

[UNGN]

The shock at full extension and/or the upper control arm hitting the stop usually limits the travel before the spring stops pushing.

I'm going to add some extra nuts under the top shock bushing to extend its travel and my robert adams 12" brake conversion spindles don't have a down stop. I'm going pull the front wheels off the ground this year with a D5 and drag radials, I just know it

 

[KEVINS]

Originally posted by John Larkin
But the springs must maximize the length of control arm travel to be effective, i.e. if the spring runs out of "push" at the end of it's travel, then a longer spring is necessary.

Exactly... It's best to keep the push constant up to max shock travel then allow the shock dampening to control the rate.

Can I use a spring that is longer (for the "push") but of the same spring rate (for the ride control)? And I would have to be conscious of coil bind as well.
Am I all goofed up here?

Springs are rated by how much force it takes to push the spring 1". Your car may have a 350lb spring which means that it take 350lbs to compress it 1". If you install a LONGER spring rated at 350lbs then it is still going to compress it 1". So if you install a longer spring it will have to be softer to maintain the same ride height. Given some known spring lengths and ratings you can figure out what spring you need to go with for a given ride height.

hth's
ks

 

[KEVINS]

Originally posted by UNGN
I'm going to add some extra nuts under the top shock bushing to extend its travel and my robert adams 12" brake conversion spindles don't have a down stop. I'm going pull the front wheels off the ground this year with a D5 and drag radials, I just know it

We want a Video when it happens!!!! That's be soo cool on DR's!!!

ks

 

[John Larkin]

The shock! That's the part of the equation I was missing. I couldn't visualize what was limiting the front control arms other than the bump stops. Cool, I think I can figure this out now, well maybe....Anyone have an old coil spring that they could take some measurements off of such as inside diameter and wire thickness? A little algebra and perhaps a solution can be found. Another question, could I use a spacer under the spring to increase it's travel range or would that lend toward coil bind problems?

 

[KEVINS]

LOL... Don't ferget the shocks when you go racing

The amount of travel is limited by the length that the shocks can physically extend or by the rubber bumpers on the frame under the upper control arms. If you install a spacer under the springs then you will raise the front of the car but not increase the travel. If the front is raised you will decrease the amount of available travel. Installing spacers is ok if you have some springs that are too soft and want to raise it back up to a better ride height.

ks