OK...this has been driving me nuts trying to find comparable data for all 3. (Mostly the IPL) Everyone says 20% increase. But I want to see the rates. So what I've done is consolidate what I've found here.

OEM G37S Coupe
F - 8.5kg/475lbs
R - 8.2kg/459lbs

IPL
F - 9.8kg/549lbs
R - 8kg/450lbs

Swift
F - 10.3kg/575lbs
R - 9.7kg/542lbs

Sources
https://www.myg37.com/forums/brakes-...rwd-coupe.html
Both pages

Swift Springs USA

Then a quick kg to lbs spring rate calculator.

Do these numbers look right?

 

"Front spring rates have been increased 20% over the base G Coupe and rear spring rates increased 10%. Shock tuning has also been adjusted."

The Full Review
2011 Infiniti IPL G37 Coupe - Overview, Specs, Pics, Video | JapaneseSportCars.com

I know the Sport version had the sport tuned suspension...so maybe the 20% applies between the Base and the IPL. If I wanted to go IPL stiffness, all I'd really need is the front 2 springs and maybe find some used struts to match the springs. I think IPL is really only good for stock-ish ride height. Swift for me most likely.

 

The 20% is from the sport up and not base.

 

A 20% increase would be 10.2/570lbs and not 9.8/549lbs. I've looked everywhere for the Base numbers. Any help for comparison purposes would be appreciated. Perhaps they thought they could round up to 20%.