Hey Guys...what is the difference between PROGRESSIVE and LINEAR springs?

Thanks.

 

thats an easy one... and im not a mechanic

linear provide the same amount of resistance for a good portion if not the entire range of movement...

progressive springs get stiffer the more compressed they are.

ppp

 

Maybe the same thing Potty_Pants said but said differently, with progressive springs the initial response is soft with the springs providing progressively firmer response as compression increases. Linear springs provide the same response, from initial impact through bottom out.

 

All progressive lowering springs offered for the G and Z use a design that will transition from a softer rate to the firmer final rate very quickly if not faster. Their are 3 way's to make a spring progressive. 1. Make a portion of the spring with coils that are much closer together, when the close coils bind the higher final rate takes over, no easy transition. This is the design used by all progressive lowering springs offered for the G and Z. 2. Vary the outside diameter of the of the spring, the narrower portion of the spring will be firmer then the wider section. Only two springs for the G or Z use this design that I've seen and their both used in coilovers, KW and HKS LS+ rear springs. 3. Vary the wire diameter in the spring itself, any portion with thinner wire will have a softer spring rate.

This is a cut and paste of a file I keep on hand on the subject.

Their is more to progressive springs regarding the compromise on performance for ride quality. Progressive rate springs are a bad idea for aggressive driving for several reasons. Soft initial compression of the springs allow the car to roll more on turn in, then the momentum built up by this roll hits the firmer part of the spring. This puts a heavier load on the outside than linear springs because the linear springs would not have allowed as much roll in the first place. And most progressive springs don't have "seamless" transitions in rate. They change rate in significant steps as active coils bottom on each other. A sudden change in spring rate, while at the traction limit, can result in a nasty slide. And further still, a progressive spring has two or more rates on one spring, right, that's what makes them progressive. ...let's assume that for the first 3 inches or three coils, the rates are 250lbs per inch and that for the next two inches, the rate is 350 lbs per inch. Therefore, when at rest, suspension will be compressed on the 250lbs spring section, and the next inch of movement will be in the 350 lb per inch range.

Now let's use the same scenario......a corner is entered and the outside spring is compressed one inch and the inside spring is extended .75 inch...rememeber the rates!

Now you encounter a bump in the corner...and since you are currently using the outside spring at a rate of 350 lbs per inch and the inside spring rate of 250 lb per inch... and the suspension is compressed the additional two inches....what happens to the spring rates? Since they differ, the chassis rotates around the roll axis... and the vehicle attitude changes/rotates differently than when in steady state cornering! Its motion becomes slightly skewed since to offset the bump deflection each spring must work through a different spring rate! If you were to then hit another bump, the attitude would change again...and so forth. All of these things of course would not happen with linear springs.

Progressive springs can be made to work in very limited conditions where the parameteres are well known, like a specific road course where telemetry is constantly giving feedback to help select the right rates.


Eibach G35 Coupe progressive springs vs oem linear springs
Spring rates in lbs first number is the softer initial rate 229/337 front 274/463 rear

Eibach coupe spring stiffness to oem as seen in a right hand corner because of the progressive spring rates, on a linear spring system, like the oem setup use’s, you would NOT see a difference left to right. (reverse for a left hand corner)
LF +7% RF -27%
LR +35% RR -20%

Coupe on 350Z RSR linear springs right hand corner
LF +10% RF +10%
LR +22% RR +22%

 

Thanks Guys for all your input.

Gsedan35...that was very informative.

So basically if I understand this right....in terms of RIDE QUALITY....eventhough the Eibach progressive springs drops the car by 1.1" city / highway driving will be similar to the OEM linear springs set up? or will it be softer?

Chico