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Discussion Starter #1
In my 70 Mustang (leaf spring, and stick car) I recently changed the the front springs in the coilovers from a 350lb 10" spring to a 250lb 11" spring to see if it helps with weight transfer. For the coil overs (Viking), the 250lb 11" is the longest conical spring they have so figured I would give it a try.

My concern is that with the new spring and to get a decent ride height (see side pic below), the 11" spring is compressed to 6", so a 5" preload (45% compressed). From everything I have found around 35% would be the target.

So my question is, what is the implication of this additional preload? (Local track is just opening so have not been there yet) This is 90% used on the track with limited street use now.

Thanks!

Here are some additional details:
  • At current ride height front end has about 6.5" of travel.
  • Scaling the car (race ready):
LF=989 lbs, RF=939lbs
LR=798lbs, RR=714lbs
3440lbs total, so a 56% front, 44% rear weight distribution. Not a whole lot I can do to shift weight to the back without going to light weight panels in the front. (Battery is already over RR tire)

* Calvert Split Mono-leafs and Caltracs
Shocks front/rear are Viking Crusader DA's

 

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I personally want the front springs to un-load at about the same time as the suspension tops out, upsets the tire weights a lot less when the tires lift off, especially when one front tire lifts off before the other. If you were able to measure tire contact patch weights with the car in motion, more preload causes an increasingly more abrupt transition when the front suspension tops out. Not a problem if you have enough power to keep the front in the air, but when you don't have the power to keep the front in the air there's a problem. The front tires get jerked off the ground harder/higher if the springs were preloaded, which causes the front to then drop faster, faster front drop causes more weight to get transferred back to the front, more weight transferred back to the front in-turn reduces weight on the back tires.

Spring preload also makes a car harder to control when it gets out of shape, especially when low pressure slicks, spools, and anti-roll bars are involved.

Grant
 

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The taller lighter spring should work better. More stored energy. If you cant get the ride height you are looking for then you would need a heavier spring. Shock adjustment will control the rate of extension and compression
 

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Discussion Starter #5
Thanks for the feedback folks. I will try them out at the track in a week and see how they are. I still have the 350lb springs if I have to put those back in. With the 350 ones the car launched nice and straight with both front tires fairly equal in the air and there were no handling issues. Just trying to improve the weight transfer on the launches.

With the 350lb springs, the front DA shocks still had quite a bit of range left so I should still be able to control the rise well.

I will keep in mind the comment on harder to control if something goes wrong.
 
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