Returning to this thread with new info, much of it contradicting what we (especially me) thought was true.
The other day Rich Bratton sent me a pic of the bumpstops inside of a Bilstein B8 strut insert. The bumpstops are ~3" of, I dunno, maybe polyurethane. The fact that the bumpstops are so tall is significant.
Lets assume that at full compression those 3" of bumpstops can squish down to 1". That’s jibes with my finding above when I attempted to fully compress a front corner and found 23mm of strut still above the gland nut.
Up above I ballparked our H&R spring available bump travel at 30mm. So imagine the insert’s bumpstops compressed from 3" to 1" at rest. 1" + 30mm is about 2 1/4". So at rest with H&R Race springs we already had our bump stops compressed by ~3/4". That would have had a huge impact on our effective spring rate. Because we didn’t just have 275lbs/in from the spring, we’d have had the sum of 275lbs/in + the spring rate of the bump stops squeezing down.
I did some poking around and it looks like 200lbs/in is a reasonable estimate for the spring rate of our B8 bumpstops. So our old front effective spring rate was ~515lbs/in (315+200) and our new front effective spring rate is ~725lbs/in (525+200).
Conclusions.
-
Our new front springs didn’t increase our effective front spring rate as much as we thought. 315 to 525lbs/in is a 67% increase. But when we take into account the bump stops the effective front spring rate increase was approx 515 to 725lbs/in. Only a 41% increase.
-
The fact that we never really get off of our bumpstops has to be beating the shit out of our front ends. We’ve certainly seen torn sheetmetal around the strut towers.
-
Eventually we’re banging out our polyeurethane bump stops and turning them into soup. So after a while the additional effective spring rate goes away, our front end gets softer, but then we REALLY bash the shit out of our strut towers when we bottom out. That fits anyone’s experiences?
-
There’d been lots of talk about how much more fun the new springs are on fast sweepers, and how they make the slow guys (like me faster) and therefore tighten up groups. This is particularly evident at Roebling Road where midpackers are 1sec faster and back packers 2secs faster. But now that we understand(?) the bump travel limitation of the B8, some other advantages come to the fore.
a) You can raise your front up a bit and gain some bump travel. So it’s not “woohoo, I have stiffer springs.” It’s "woohoo, I finally have the height adjustibility that gets it off of the damned front bumpstops.
b) The narrow spring and no tophat creates a more level camber playing field. Because of tweaked frames, some people used to be able to get a lot more camber than others and that’s not fair.
Just for clarity, the problem is not that the B8 is a shitty strut insert. The problem is that the B8 is tall. It has to be because it’s designed for the relatively tall OEM strut housing, which was designed for OEM ride height. We’ve lowered our cars so the height of the strut housing causes bump travel issues. Had Carter, years ago, wanted to spec a more appropriate height strut insert, he would have had to tell everyone to either shorten your strut housings or buy aftermarket housings. Both of those ideas add cost, so it’s easy to understand why he’d be wary of that route.