The GT-R comes stock with progressive rate springs, meaning they are softer when extended and stiffer when compressed, by having the coils wound tighter at one end of the spring. So initial spring rate is low, moving up to a higher final rate at limit cornering or in bump. The Eibach springs were designed not to change the rate but simply to lower the ride height. I spoke directly to an engineer at Eibach about this. So they will not be softer than the OEM springs.
http://www.nagtroc.o...post__p__381960
"I spoke to David Cortez at Eibach today about their spring kit and about the stock GT-R spring rates. He was very helpful and here is what he told me.
Stock spring rates (Eibach's own measurements on a GT-R in Germany):
Front : 119 N/mm average rate (0, +- 20 mm deflection, +- 40 mm deflection). Max rate is 151 N/mm or 862 lbs/in. At static ride height, rate is 140 N/mm or 799 lb/in
Rear: 67 N/mm average rate (0, +- 20 mm deflection, +- 40 mm deflection). Max rate is 78 N/mm or 438 lbs/in. At static ride height, rate is about 68 N/mm or 382 lb/in.
Eibach spring set rates (product # 6389.140):
http://eibach.com/cgi-bin/htmlos.exe/08142...421399500022212
Front : average rate not given. Min rate is 399 lb/in. Max rate is 948 lbs/in. At static ride height, rate is 948 lb/in as soft coils are touching.
Drop is 0.8"
Rear: average rate not given. Min rate is 188 lb/in. Max rate is 485 lbs/in. At static ride height, rate is 485 lb/in as soft coils are touching.
Drop is 0.5"
They use progressive rate springs to essentially control the static ride height (saves using a second tender spring and spacer), and with their design, the static spring rate is the same as at full compression. Their goal was to increase front and rear spring rates by a modest 15-20% and to slightly drop the ride height. That way dampers can handle the new springs without requiring a change in valving."
So Eibach springs are stiffer than OEM.
http://www.nagtroc.o...post__p__382490
"Actually the progressive wind type is different on the OEM and Eibach springs. At static ride height, the Eibach springs are in the 15% stiffer range than OEM, but as the OEM spring compresses, it gets stiffer while the Eibach is already at maximum stiffness (starting before static ride height compression), and at that point the Eibach springs are only 10-11% stiffer than OEM. Most people would not feel much difference. Eibach springs mostly lower the car slightly, not requiring new damper settings."
The Swift springs are said to be progressive as well, and are designed to lower the ride height, essentially doing the same thing as the Eibach springs.
Swift/MCR's
Spring rate:
Front 5.4kg to 15kg, 302lbs - 840lbs
Rear: 2.4kg to 7.0kg, 134lbs - 392lbs
They provide a 1" drop"
So based on the Eibach measurements of the OEM springs in Germany, the Swift springs are virtually identical in maximum rate to the OEM springs, except in the rear where the Swift ones max out at 392 lbs/in versus the OEM rears at 438 lbs/in max. I doubt you could tell the difference as it is only a 10% change.
A large part of the stiffness is the run-flat tires as others have mentioned, and the damper valving. Even in comfort mode, the damper valving is very stiff. It is apparently better in the 2012's, but they have also made many other changes in the 2012's suspension, including changing the suspension arm geometry, caster, etc. So just changing to those 2012 dampers might not gain you as much in comfort as one might hope, but I don't know of anyone who has tried that. Another item is the stiffness of all the bushings, which is not something you can alter by going to softer bushings. I am not aware of any softer springs for the GT-R, or softer dampers. And when you go to race mode, it is just the damper that changes valving, so you cannot go to a softer comfort setting and maintain the same stiffness in Race mode.
I think pretty much the only option is tires with a softer sidewall, or custom springs, or a pillow.
