hi guys currently looking at a spring swap on my car, basically with the state of the roads where I live the ride is quite harsh with potholes etc. I'm currently running kyb excel g shocks and eibach springs, so considering going with oem springs. are tt/ na springs the same? my other option is swapping my wheels from 19's down to 18's 

I'm running the KYB AGX Eibach combo. The Eibach springs have a 0.8" drop over OEM which removes the "4x4" look with larger than stock wheels.

The picture below shows my car on OEM springs with 18" wheels before fitting KYB/Eibachs.

The spring rates for OEM (US market) and Eibach springs.

http://twinturbo.net/nissan/300zx/forums/technical/view/1080906/300zx-OEM-Spring-Rates-Vs-Eibach-Aftermarket-Spring-Rates.html

UK spec is TT Front: 146 lbs/in and TT Rear 146 lbs/in (from FSM)

great thanks Andrew, I may look at the 18" wheel option first and try to get a little more rubber between the rim and tarmac, as there isn't a lot with 19s which may help, it's mainly when I hot potholes the car hits them hard. 

 

My Z profile pictures shows the extra sidewall depth you get with 18" wheels and tyres. The Michelin PS4 tyres have

quite flexible sidewalls compared to some other brands I have used.