I did tons and tons and tons of research on this topic and I ended up fairly happy overall with the end result. This post includes a review of the Eibach 6399.140 and the H&R 53030/53031 on a 2012 G37xS sedan.

Lowering springs are very limited for the 2010+ G37x sedan. The only real spring options are Swift, Eibach, or H&R. Otherwise you are forced to kick out $1000+ on coilovers.

Eibach 6399.140
The ride comfort was superb. Overall handling was improved and smooth. I was not happy with the Eibach 6399.140 drop because the front was not lowered enough and the rear was way lower than the front (over 1" difference). When I had the Eibachs installed, my front fender-to-ground was 27". I had someone measure the Swift springs drop and it was nearly the same. I wanted something a bit lower so I decided to go with H&R springs.


H&R 53030/53031
I heard so many bad things about H&R springs such as: "You will scrape everywhere, you would bottom out everywhere, you will ruin your tranny by scraping, you will blow your struts quickly". The only comment that may be fairly true is that you will likely blow your struts sooner since there is very little strut-travel since it's moderately low.

The H&R front springs lower the front of the car moderately but there is very little travel for the struts. City driving can be jarring if the streets are bad, but suburban neighborhoods and highway driving is fine. This was acceptable for me since I love the drop and the car sits perfect. The main issue with the H&R springs is that the rear H&R 53030 springs will never work on the AWD sedan. They literally slam the rear of the car and the tire was almost completely tucked.

I was forced to keep the Eibach rear springs and H&R front springs and the drop is perfect and I have no problems cornering with the different springrates.

Front: H&R 53030
Rear: Eibach 6399.140



Front: H&R 53030
Rear: H&R 53030

 

how was the install?

 

That's very interesting. Thanks for the 411 on using both types of springs.
Sedan looks good!

 

Install wasn't that bad. Spring installs are always a PITA since you have to use the spring compressors but an impact wrench makes life so much easier. Without an impact wrench I wouldn't even attempt it. It takes about 3 hours for the front and 1 hour for the rear.
Thanks. I had to do so much research in order to find this out but I'm finally happy.