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I inquired about getting just the front springs to lower the front end only (you can) from Eibach.
A response email from Eibach:
"Unfortunately, length of the spring has no connection to the spring rate. We have springs that are longer than stock springs, but still give an aggressive drop."
My response:
"I know that spring rate and length are not directly related, but a "longer spring that still gives an aggressive drop" is a lower-rate spring than stock, by necessity.
"If a spring's rate is 1000lb/inch it has to be a longer spring, initially, to end up with a lower installed height than a spring with a 2000/lb/inch rate.
"But a 1000lb/inch spring will be more likely to allow the car to bottom out even if both springs are the same installed height, much more if the 1000lb/inch spring is a LOWER installed height. For a lowering spring, to keep the front end safe from bottoming out, I would need a spring that was both lower than stock, and had a higher spring rate at the installed height.
"If and only if your spring has a higher spring rate at its installed height as the stocker at its higher installed height, it would not be more susceptible to bottoming out.
"I understand that the spring can be designed for a progressive rate to allow full travel on rebound while still preventing the car from bottoming out on compression better than the stock spring. What are the compression distances and rates of your front springs versus the stock springs, at full compression of the suspension, full rebound of the suspension, and at whatever they end up at resting height?"
I will see how it goes.
BTW, the further your coils are spaced, for a given wire size, the stiffer your spring rate is going to be, with the limit being solid rod behavior. The tighter your coils are spaced, the softer your spring rate is going to be.
ADDITIONALLY, ATTENTION VALVE SPRING MAKERS, the smaller-diameter your coil is for a given wire size, the higher your spring rate will be. This is important, especially, for valve springs, as it means that near the end of the valve's rebound (opposite of compression,) the valve spring is transporting almost the entire spring mass, which is not desirable. Beehive valve springs, for ideal springing, would be smaller at the bottom and wider at the top.
Look at it this way, if you view the wider coils as an incompressible solid mass that merely adds dead weight, at what end of a progressive-rate spring's travel would you want it?
For a suspension piece, the bottom of the spring is wagging back and forth, while the top of the spring is stationary, so wide coils at the bottom are acting more like dead, unsprung mass.
For a valve spring, the top is wagging back and forth the entire length of travel for the valve lift, while the bottom is remaining stationary. When installed, it makes more sense to put the softer coils at the end that travels the most.
What makes me marvel is that spring makers put the wider-spaced coils at the bottom of the spring, just as valve spring makers put the narrowest-diameter coils at the top of the spring, so the spring has to deal with the entire unsprung mass of the harder coils even when softer spring engagement is being used.
Mercedes used to have a FWD system (might still have) that has the half-shaft going right THROUGH the spring coil where the coil was spaced very widely. They could do this, as the wide coil, being stiffer there, as widely-spaced coils are (per inch of travel) the coil would not compress sufficiently at that spot to "bite" the half-shaft.
Just some physics that I have encountered.
Now, if when installed, the narrower suspension coils actually BIND somewhere in the spring's travel, it would then make sense to have the narrowest coils at the top, since THEY would be the ones acting more like dead weight.
Update: ("Updating" not to be confused with blokes who are "punching above their weight," in the woman they are dating,) Eibach told me that the softer, closer coils bind upon install at normal driving height when the car is level, leaving the higher-rate portion of the spring that is unbound to do its work, and, I quote: "The front OE rates if I remember correctly are about 320 lbs/in, whereas the Eibach rates are 376 lbs/in springs" when installed, which is a great design feature, as the coils are still there for travel if the suspension goes into full rebound, but are out of the unsprung mass equation when they are quiescent, at the top of the spring.
"The part number for the front is 4.9528F and they are $144 each "
PS they lower the car 0.6" at the front axle centerline, so, maybe 0.78" lower at the front spoiler?
How much better customer service could you possibly want?
Good work, Eibach.
PS 144 bucks each? That is cheap for reduced drag, cooler look, reduced bottoming, better airflow through engine compartment, and increased downforce.
A response email from Eibach:
"Unfortunately, length of the spring has no connection to the spring rate. We have springs that are longer than stock springs, but still give an aggressive drop."
My response:
"I know that spring rate and length are not directly related, but a "longer spring that still gives an aggressive drop" is a lower-rate spring than stock, by necessity.
"If a spring's rate is 1000lb/inch it has to be a longer spring, initially, to end up with a lower installed height than a spring with a 2000/lb/inch rate.
"But a 1000lb/inch spring will be more likely to allow the car to bottom out even if both springs are the same installed height, much more if the 1000lb/inch spring is a LOWER installed height. For a lowering spring, to keep the front end safe from bottoming out, I would need a spring that was both lower than stock, and had a higher spring rate at the installed height.
"If and only if your spring has a higher spring rate at its installed height as the stocker at its higher installed height, it would not be more susceptible to bottoming out.
"I understand that the spring can be designed for a progressive rate to allow full travel on rebound while still preventing the car from bottoming out on compression better than the stock spring. What are the compression distances and rates of your front springs versus the stock springs, at full compression of the suspension, full rebound of the suspension, and at whatever they end up at resting height?"
I will see how it goes.
BTW, the further your coils are spaced, for a given wire size, the stiffer your spring rate is going to be, with the limit being solid rod behavior. The tighter your coils are spaced, the softer your spring rate is going to be.
ADDITIONALLY, ATTENTION VALVE SPRING MAKERS, the smaller-diameter your coil is for a given wire size, the higher your spring rate will be. This is important, especially, for valve springs, as it means that near the end of the valve's rebound (opposite of compression,) the valve spring is transporting almost the entire spring mass, which is not desirable. Beehive valve springs, for ideal springing, would be smaller at the bottom and wider at the top.
Look at it this way, if you view the wider coils as an incompressible solid mass that merely adds dead weight, at what end of a progressive-rate spring's travel would you want it?
For a suspension piece, the bottom of the spring is wagging back and forth, while the top of the spring is stationary, so wide coils at the bottom are acting more like dead, unsprung mass.
For a valve spring, the top is wagging back and forth the entire length of travel for the valve lift, while the bottom is remaining stationary. When installed, it makes more sense to put the softer coils at the end that travels the most.
What makes me marvel is that spring makers put the wider-spaced coils at the bottom of the spring, just as valve spring makers put the narrowest-diameter coils at the top of the spring, so the spring has to deal with the entire unsprung mass of the harder coils even when softer spring engagement is being used.
Mercedes used to have a FWD system (might still have) that has the half-shaft going right THROUGH the spring coil where the coil was spaced very widely. They could do this, as the wide coil, being stiffer there, as widely-spaced coils are (per inch of travel) the coil would not compress sufficiently at that spot to "bite" the half-shaft.
Just some physics that I have encountered.
Now, if when installed, the narrower suspension coils actually BIND somewhere in the spring's travel, it would then make sense to have the narrowest coils at the top, since THEY would be the ones acting more like dead weight.
Update: ("Updating" not to be confused with blokes who are "punching above their weight," in the woman they are dating,) Eibach told me that the softer, closer coils bind upon install at normal driving height when the car is level, leaving the higher-rate portion of the spring that is unbound to do its work, and, I quote: "The front OE rates if I remember correctly are about 320 lbs/in, whereas the Eibach rates are 376 lbs/in springs" when installed, which is a great design feature, as the coils are still there for travel if the suspension goes into full rebound, but are out of the unsprung mass equation when they are quiescent, at the top of the spring.
"The part number for the front is 4.9528F and they are $144 each "
PS they lower the car 0.6" at the front axle centerline, so, maybe 0.78" lower at the front spoiler?
How much better customer service could you possibly want?
Good work, Eibach.
PS 144 bucks each? That is cheap for reduced drag, cooler look, reduced bottoming, better airflow through engine compartment, and increased downforce.
