MAGK944

[QUOTE=PorscheG96;12448194]...so if you were to add a 250# helper spring...a 171# spring rate....a 3 or 4" helper.../QUOTE]

Interesting reading, however I cannot figure out how that short helper would not simply bind from the static corner weight of the car, rendering it useless. Surely you would be better off fitting a progressive spring to achieve the same goal. What am I missing?

PorscheG96

Since when does suspension travel only begin from static ride height? The suspension is always moving up and down so the more you unload it, the more you'll engage the lower rate as it loads up again. Why are you surely better off with a progressive spring? A progressive spring would work the same way but there aren't many to choose from. Plus the progressive low rate might be blocked at static height like you say...

MAGK944

I think you misunderstood my query.

You are using a 4" helper with an effective spring rate of 171 lbs per inch, and the car has a corner weight of say 750 lbs acting on that spring and the helper will compress first. The helper spring will be binding even before you start moving.

750 lbs on a 171 lbs per inch effective helper spring means that helper is going to compress (if it could) 4.4 inches. Your 3-4" helper is in bind from the start.

Not trying to disagree with your post, just trying to figure out what I am missing here

PorscheG96

This is incorrect. The theoretical helper rate is 250#. 171# is because the main spring compresses too.
This is incorrect, the spring doesn't support entire corner weight, just the unsprung weight. But with a driver the 750 lbs is reasonable.
This is incorrect. Both springs compress at the same time.
Who cares? If the suspension has 8" of total travel and you're bound for 3" then you'll have the softer rate for most of the travel, especially over bumps that cause the suspension to rebound and compress, which is how a basic suspension works.

I have this setup and have competed with it + driven on the street. It works. KW V3 is basically the same thing where the helper is blocked with vehicle static but rides way better than without helper [also due to high speed bypass valving]. Or you can add a bit more helper rate like 350# which will def have a bit of travel left at static but result is almost exactly the same. 750 / 350 = 2 and smidge inches of travel. You can get a 3.5" helper with 1" block length and have the soft travel left over at static if you want...but most rebound and compression travel will occur with the 213# rate [550*350/550+350]. Imagine going up over a crest and down into a trough -- your wheel extends past static to stay in contact with the road and a 213# initial rate will absorb the impulse on the way down before 550# main stops it. That's nice.

MAGK944

Thanks PorscheG96, that makes sense to me now. I assumed that on a dual spring set-up the weaker (tender) spring compresses first, then the main spring starts to compress. Hadn't thought that they both compress at the same time.

OP apologize for going OT....carry on

Dwane

Carbon coby of the 2 above. Basically a DE car with little street. Fine on the 1.5 hour drive to Tremblant...completely gutted.
Found the front a little floaty on mid-corner exit...bumped up the front camber to -3 this year and it made a difference. Going with -3.2 next season.

JustinL

I'll put mine (racecar) up too for another datapoint:

Front:
255 wide r-compounds
675lb springs
Bilstein escort cup
Charlie arms
All monoball bushings
Tarett sway bar

Rear
275 wide r-compound
675lb springs
Bilstein escort cup
All monoball and solid bushings
Tarett sway bar

Weights with 1/2 tank and 155lb driver:

689...669
652...630
Cross weight 50.0%
Total weight 2640

Well balanced and well within the fine tuning I can do with just sway bar adjustment. It's a bit loose on heavy braking with the Torsen diff, understeers slightly on corner exit.