Spring rate questions...

**Mr. Luos** · 08-23-2007, 05:07 PM

I am just starting to understand spring rates. The lower the number the softer the spring and the more motion it has, correct?
Also...how exactly does a progressive spring work? Gets stiffer as pressure is on it?? What about lifting off it??

My car is currently on the ProKit with stock shocks. I love the stance, and the ride isn't that bad. But it performs pretty weak at the track.
I am looking for a good spring to compliment both drag and street.

Car sees 95% street time, but when I do race, I want it to do well.
How are BMR or Hotchkis springs on the strip? Will also be replacing the shocks this winter, but undecided on those as well.

Thanks in advance!!!!

**Eugenio_SS** · 08-24-2007, 08:23 PM

i'd stay w/ the same springs and just get shocks that will dampen the given spring rate properly.
You'll see an increase in confort and a great increase in handling.
The way the car is now, it's underdamped, since the shocks cannot handle the spring rate... that means your car is bouncing more than it should... the shock is not able to absorb the energy levels.

To answer your question about progressive springs.
Let's understand spring rates, first.
a linear spring means that the spring rate is the same throughout the compression of the spring.
Front prokits are 400 lbs/in, for example.
that means that every 400lbs you put on the spring will compress it by 1".
you put 800lbs, the spring will compress 2", etc.
a progressive spring, let's say 300-600 lbs/in
This means that when the spring is uncompressed (car lifted) it takes ~300lbs to compress the 1st 1"... as the spring compresses, the rate increases, requiring more weight to compress 1" as you compress the spring. When the spring is close to fully compressed, you need 600lbs to compress a 1" @ that position.

Now, assume you have a spring as specified above (300-600 lbs/in), and let's assume that @ resting position (simply the weight of the car on it) that you are @ ~450lbs/in.
The tricky question is how you setup a damper (ie shocks) to absorb the spring rate, so that you get good characteristics ?
Let's say you adjust damping to absorb 450lbs/in well... not a problem on silky roads and not compressing/lifting the spring.
What happens when you hit imperfections, holes, or start pushing the car ?
Well... the spring rate changes.
If you hit a pothole and the spring uncompresses, the shock will overdamp the spring, not allowing the spring to do its job.
If you compress the spring, bump or load the car on cornering, the shock won't be able to handle the increased spring rate. That's why it's hell to have progressive springs if you want confort and/or handling. You'll basically endup with a mismatch of shock/spring setup, like you have now... and this creates a harsh ride (mismatch on setup, quite different than stiff... you can have stiff and properly damped and not harsh... for example, i have 500lbs/in in front and car is more confy than stock... lol)

If you were to have a fixed spring rate, such as the prokit @ 400lbs/in, you simply need to get a shock for those specs and it'll work the same regardless on how compressed the spring is, so you get excellent damping throughout the range, giving you predictability, proper damping and by consequence, confort and handling.

Hope this helps.
So basically, i'd recommend you get Bilstein revalved and keep the prokits.

On the other hand, to add some thought to it:
If you want to "increase" the rate, you can always do so with swaybars, only getting the equivalent of more spring rate while turning/cornering without affecting your daily confort with high spring rates (stiff).

My 2 cents... hope it helps.

**Mr. Luos** · 08-25-2007, 04:35 AM

100x times more helpful than what I have gotten so far.
Ride wise, I am not too concerned. It is a sports car, I don't mind feeling the road.

My biggest thing is to make sure it does well at the track. Hard enough to launch an M6 effectively. But at the same time, I don't want to be driving on drag springs.
I was thinking BMR spr ingswith Koni SA's. Now...the Koni's might not be on there for some time.

Thinking BMR because they give me a little more ride height (I sit LOW on the 15" ProStars) and are a touch softer it looks like.
Ideas?

**ycems779** · 08-25-2007, 09:28 AM

Hello Guys Mr Luos Check Out The Two Kits I Found On Ebay And Was Thinking About Buying , Also Eugenio Would You Give Your Opinion On These Kits For Us .
http://www.ls1.com/forums/showthread.php?t=61198

P.s. Sorry Mr Luos Didn't Mean To Hijack We Are Both Looking For Same Thing And Thought This Might Help .

**Mr. Luos** · 08-25-2007, 10:33 AM

Bilstein > KYB

Keeps You Bouncing

**Eugenio_SS** · 08-27-2007, 08:23 PM

BMRs are exptremely progressive.
since you are considering the Koni's, just get those and keep the prokits... less $ and better combination.
I was suggesting the revalved because they'd fit well and cheaper than the koni's.

**DanWS6** · 08-28-2007, 02:05 PM

So besides the prokit what spring would work good with konis?

**Mr. Luos** · 08-28-2007, 03:27 PM

Originally Posted by Eugenio_SS

BMRs are exptremely progressive.

Okay...so, why do they make progressive springs if they are bad?

I am a little confused for sure about this.

**awSSum01** · 08-29-2007, 08:37 PM

Eugenio_SS previously wrote...
So basically, i'd recommend you get Bilstein revalved and keep the prokits.

Sorry for my ignorance...but what are "revalved" Bilstein shocks? Is this a modification or a specific style of Bilstein shock? I am planning on going with the Eibach ProKits but I want to make sure the shocks are appropriate.

Thanks for the assistance!

**Mr. Luos** · 08-30-2007, 03:07 PM

Originally Posted by awSSum01

Sorry for my ignorance...but what are "revalved" Bilstein shocks? Is this a modification or a specific style of Bilstein shock? I am planning on going with the Eibach ProKits but I want to make sure the shocks are appropriate.

Thanks for the assistance!

They are Bilstein shocks valved to handle the ProKit spring rate. Strano revalves them...$525 a set last I checked.

**Eugenio_SS** · 09-11-2007, 01:05 PM

Originally Posted by Mr. Luos

Okay...so, why do they make progressive springs if they are bad?

I am a little confused for sure about this.

Some will disagree w/ my opinion on this one, but who cares.
1st, BMR has no clue about suspension setup... they only have clue on straight-line performance... and their products are aimed for 1/4 mile customers.. not handling.
2nd, the idea behind a progressive spring is great... the problem is that shocks can't handle varying spring rates... they are designed to dampen, and limited on the range of rate, for a given valving.