Originally Posted by JAJ
We're doing exactly the same math. Zero preload, zero drop = 200#, zero preload, 1 inch drop = 160#.
According to the advertising, Eibach drops the front 0.8" (yielding 166#), H&R drops it 1.0 # (yielding 160#) and Dinan drops it 1/2" (yielding 177#).
Dinan is the only one of the three with the opportunity for stiffer than stock springs, and there's no way to know if they actually stiffened them or if they did a shorter stock-rate spring and a smaller pre-load.
I would like to point out a few facts:
1. Based on my hands-on experience, H&R is stiffer than Dinan, and Dinan is slightly stiffer than stock.
2. H&R is shorter than Dinan, and Dinan is shorter than stock.
3. All three have some type of preload. Stock over 2", Dinan roughly 2", and H&R around 1.5".
4. Static compression on stock springs is not 4". It is actually around 3" max.
The shock only has 5.75" of travel; the bumpstop compresses to around 1" max. Therefore we would only get 5.75-4-1=0.75" of bump travel based on 4", which is unrealistic.
So how is it possible that H&R is stiffer and create a drop vs. stock? The key is preload.
According to #2 above, the stock spring is preloaded by more than 2", which means about 300 to 400 pounds or roughly 50% of the unsprung weight per corner "disappears", which means only 50% of USW is actually used to compress the spring from its perch-to perch-length.
H&R has a lot less preload, which means more unsprung weight is used to compress the spring from its perch-to-perch length. This is how it gets away from being stiffer and providing a drop.