From a word file I keep on hand.

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
229/337 front 274/463 rear
F +7% R +35% (looking at peak rates only)
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)
RF -27%
RR -20%
LF +7%
RR +35%

Eibach G35 Sedan
259/334 front 359/413 rear
F +6% R +21% (looking at peak rates and in comparison to a sport suspended sedan)
F +18% R +34% (looking at peak rates only and in comparison to a non sport sedan)
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)
RF -17%
RR +5%
LF +6%
LR +21%

 

wow.. that is definitely very comprehensive. i'm a little short of understanding it completely, but i get the general idea. Great post!!! =]

 

came in trying to learn something...

going out lost

 

Thank you everybody for your responses, but any pics of Gcoupes lowered with 350Z H-techs? Also what size tires are you guys using?

 

There seems to be a lot of people with a lot of knowledge in this thread so maybe somebody can tell me why. I order a set of rear 350z springs the revised version for my g35 coupe and knowing that this springs are suppoused to be 1/2" shorter than the g35's, they ended up being the exact same length. can any body help?

 

^^^not too sure i get it, same height as the stock springs???

 

I want to see a stock(no lip or bodykits) with 350Z H Techs on 20's. Am I asking too much?

 

Here you go...Z Htechs, 245/35 and 275/35/20's.

 

That's a great drop. Do you have to use any camber kits? I searched, seems like some people do, others don't on the coupe.

 

I was able to get it aligned within spec without camber kits and toe bolts.

 

That is a beautiful drop! I'd love to have my car with that drop, but with my bodykit, I'm already pushing it... especially since my car is a daily driver.

 

Thanks sponger it is sweet! How much do 20's raise the car? 20's and Z H Techs seem to be the ticket! How come some people can't get camber corrected and some can????

 

I'm wondering the same thing as Cactus... I know no two cars are going to be exactly alike but there seems to be big differences in camber and toe based on alignment numbers some have posted.

 

Thanks fellas. I guess the different alignment outcomes has to do with the shop performing the alignment. Make sure you take to a knowledgeable shop.
Right now, the car has a nice forward rake. I wish the back was about .5" lower. Anyone here know how to do the spring pad mod?

 

Could you possibly post more pix on flat ground?