1. Which has a smooth ride?
2. Which one lowers the car more?
3. Which one is less prone to sag?

 

Good questions.. I like to know as well.

 

1. Depends on driver I suppose. Love my H&R's!
2. Roughly 1.3" front and 1.2" rear.
3. Had the Eibach Pro-kit on prior car (no issues); have H&R's now (again, no issues).

 

Did you change your Struts or you are still on the factory? if you did please let us know what type?

Thanks for the feed back.

 

Use the search button maybe?

https://g35driver.com/forums/brakes-suspension/65190-g35-350z-aftermarket-coilover-springs-shocks-spec-s-w-updates.html

^^^ Anything with lower spring rates than stock will be softer than stock, meaning "smoother ride" (Swift Sport machs are softer than stock giving you a smoother ride), but with softer springs you sacrifice performance.
Check out that link I just posted

 

I did use the search function. Keep in mind I am referring the 07' model not the older ones. I read your post very infomative, but all that information was Greek to me.

 

This is what your spring rates are (assuming you don't have sport tuned suspension)
Front: 283 Rear: 308

Now look through that list and look for a spring that has either the same numbers or LOWER numbers to get a softer spring.

 

I have to agree with you. I feel the same way.

 

This is the same for the 07 Spring?.. .

 

I do have sport. What are the spring rates of the sport and what are they for the H&R and Eibachs. I saw they were listed in that other post, but I don't think it was referring to the 2007+ part numbers on those aftermarket springs. Thanks for the help.

 

1) On the 07 sedan, the ride is just as smooth using either H&R or Eibach.
2) I'm like 90% sure the H&R will lower the front just a hair more than the Eibachs will. The rear drop using both springs is about the same.
3) Both manufaturer's springs will not sag. If there is sag from using quality springs, it is normally caused by the rubber isolators taking a compression set.

Springs rates for the stock linear springs can not be compared to aftermarket progressive rate (non-linear) springs - especially when trying to determine ride quality "by the numbers". The spring rate on a non-linear spring is a function of how much it is compressed. A well designed progressive rate spring usaully means a smoother ride during "normal" driving and "firmer" feel during hard cornering.

Lots of discussion in this thread:

https://g35driver.com/forums/v36-brakes-suspension-wheels-tires/138579-my-morning-eibach.html