Quote:
Originally Posted by thegrinchboy
Out of curiosity, do you know if the XI springs are linear or progressive?
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It looks like all rear springs I've examined are linear. ZSP and XI OEM identical shape (dead length, # coils, coil diameter) only difference being wire thickness, XI a lot thicker (so stiffer). Eibach has fewer coils, shorter dead length, and thicker wire than either. They have stated it has the same rate as OEM ZSP. SO it is the same rate but shorter dead length, that is how it gets lowered. OEM XI has thicker wire but same dead length and # of coils as ZSP so it is stiffer than either.
It looks like all front springs individually have uniform wire diameter (so no progressiveness from diameter taper in other words). The only thing that would make the fronts progressive is the slight variance in coil diameter, narrowing near the bottom needed to fit into the standard sized BMW upper and lower strut perches (or actually the pads that fit into the perches).
IOW it looks like the 3 types I've looked at, ZSP, Eibach ProKit, and OEM XI, are all mildly progressive in front, with the shape or curve of the progressiveness of rate identical due to the fact that the spring shape is identical. The only difference being wire diameter. It looks like the Eibach is the same shape as the others but I did not have it out. I have looked at pictures and they seem to all have 5 coils +/- small fraction of a coil.
I think it would be hard to get a significantly different rate curve into this form factor. It looks like only 4 active coils and not much of a diameter change from top to bottom.
I have some thought on what you said in the other thread on UUC bars, will PM you tomorrow. Answering the door for trick or treaters right now, and catching up on Walking Dead via Netflix.