Your statement regarding storing spring energy is not correct. You are completely disregarding ride height and preload. Surely you know that a spring with a lower spring rate will require more preload than a stiffer spring to maintain the same ride height. That extra preload IS stored (potential) energy. And the location matters also. The motion ratio of a stock location spring ensures it will have more preload (stored energy) at full extension (continuing to help pitch rotation) then a coilover at full extension, regardless of spring rate (hence installing trick springs is such a bitch). Since you are talking in terms of wheel rate, could you please post the motion ratio's of the stock spring location and of the coilover location?
I want to clarify what is being said and meant.
What Troy is saying is correct IF both springs are compressed the SAME distance. However the spring with the higher spring rate will not collapse as much as the spring with the lighter spring rate. It will only collapse as much as is needed to suspend the car in equlibrium. For this reason there is no "preload". My definition of Preload is "tension" that is present above/beyond the equilibrium state. So neither
spring will exert any "preload".
The below is for the front spring on a car.
So when a 450# spring in installed it WILL have the same Potential Energy (stored energy) as a 175# spring. The difference is that the 175# will be able to release the stored energy over a farther distance b/c it will be collapsed farther in the same car. This distance is what is important in a lot of drag cars b/c if the spring is only compressed 2" like a 450# spring would be BUT the car needs 5" of extension for best weight transfer the the heavy spring can not extend far enough. There will be 3" of strut extension where the spring is rattling around and then there will only be about 2" of front end lift.
Jack made the comment that "The amount of energy stored in the front springs has nothing to do with spring rate or where the spring is mounted. "
This is not necessarilly true DEPENDING how you look at it. The position of the spring WILL change the amount of Potential Energy stored if the spring is moved closer to the pivot point or farther away. The spring RATE will not change but the stored energy will.
The stock front spring location is closer to the pivot point than a coilover spring so a stock location spring will require a HIGHER spring rate than a coilover spring to obtain the same spring charecteristics. For this reason
Jack also made the comment "From this standpoint, a coilover spring that is 175lbs/in, will give a wheel rate that is around 160lbs/in. This is 60-70% more wheel rate (160 versus 90-100). This amount of increase is not going to have that much effect on ride quality. "
I disagree 100% and mainly because the coilover spring operates at a 1 to 1 ratio with the wheel where a stock spring operates at a 1 to 3 ratio (simple guess on my part) so going from a 130 coilover spring to a 175 can have a HUGE affect depending on the weight of the car.
Quote: "The higher the ratio of the rear to front roll stiffness in the car, the more equally loaded the rear tires will be on launch. The more equally loaded the rear tires are, the more total traction they can develop as a pair. The more total traction they have, the harder the car can accelerate. The harder the car accelerates, the more weight transfers from the front tires to the rear. The more weight on the rear tires, the more grip they have, again allowing the car to accelerate even harder."
While this explaination of forces to the rear tires is true it can fail in reality b/c a stiffer spring may not absorb the initial shock from the launch and cause the car to spin which defeats the purpose of trying to get traction. The car NEEDS some give to absorb the shock from the launch and the only way to do this is to use a lighter spring. I recommend a coilover spring around 110# for most cars then up/down from there but very rarely anything over a 120. If there is a lot of weight added to the rear of the car (like in a DR car) then the spring rate will have to go up to hold up the extra added weight.
Remember you can not compare the spring rates for a coilover to a conventional spring b/c the conventional spring rates will be much higher.