I've been running Z springs in the front and coupe springs in the rear for about 1.5 years (maybe longer). I put the coupe springs on the back because I had assumed the ride quality would be better and the coupe springs balance the drop since they're longer than the Z springs. Last night I was bored and decided to swap on the Z springs to see what the difference the ride quality, handling, etc would be running a full Z spring swap vs the half/half set up many of us are doing.

First, I measured the rear gap on G with coupe springs. It was about .7" with a 1/4 fuel, spare, and 40lbs of tools and softball gear. After about 10 minutes with two jacks, an 18" breaker bar, rachet, a 17mm socket, and a 17mm wrench, I had a coupe spring out. I measured the difference in height, spring gauge, and coil gap. The coupe spring is roughly .6" longer than the Z spring, is about .1" narrow in gauge, and has about an additional .6 coil. I swapped in the Z spring and moved to the other side and did the same. After lowering the car off the jacks, I was surprised to see that the gaps were about 1.5" on both sides I figured it was because of the torque load on the chassis and drivetrain after jacking up the car twice and that the car would equalize after driving for a few seconds. I rolled down the street then got out and inspected the gap. To my surprise, the gap was the exact same as the coupe springs! I drove around for an hour and tried to note the difference in handling, ride quality, etc. This is about I've noticed:

1) Ride quality is the same on most surfaces. Pavement cuts are slightly more harsh
2) Ride height in the same (measured yesterday and today after 50 miles of driving)
3) Transitional handling is quicker, less initial lean, less bouncy (nothing major)
4) Overall ride is more controlled.

 

Time for my Z springs to go back in =) LOL


Only if swapping them are easy...lol, I would wanna try that out too.

 

Thanks for the info, I'm about to do my drop soon and I couldn't make up my mind. I have a full revised Z suspension and well as newer coupe springs, but I wasn't sure which to use on the rear. You've answered that. Are you which versions of the springs were/are you running?

 

Unrevised.

 

Do you think the revised version (higher rate) will hold the back of the car up differently? I was just looking at some pics again and don't like the uneven look. The only reason I got the coupe spring set was the make the drop more even. But I would also want the better feel/handling. Uh oh I'm torn again, still leaning towards the full z though.

 

Could I maybe buy your coupe springs from you?

 

If you use the coupe springs in the rear mays the car more level and with the 350Z springs in the rear it will make the back look sagging, like the stock look. Also if you put the 350z springs on the rear you may need to get adjustable cambers to pull the wheels back into alignment. I didn't have to install adjust able cambers with the couple springs on the rear.

 

that condition is car by car basis. the only camber that was out after my z springs and alignment was the front which are not adjustable for camber. the rear was in spec after the alignment.

 

Sure, If I end up not using them. I might want to hold on to them for a while to play around though.

 

Hey DaveB, how much much of a difference was there in what you felt? I'm assuming it is only marginal. I still don't get the ride height being the same.

 

The rear ones are really simple. The front ones are very time consuming to an average person like myself.

 

I don't think the revised springs would hold up the back any differently because the ride heights on the 350Zs never changed therefore I don't the G35 ride height would change either.

I had used the coupe springs in the back to because the springs were longer therefore I figured there would be additional ride height to be gained. It turns out that the Z springs have a stiffer rate therefore they don't compress as easily as the coupe springs. The wheel gap between the shorter Z spring and longer coupe spring is within .1".

If you really want even wheel gaps at all corners, you'll need to use the stock springs in the rear (which I would not recommend). The reason the gaps are different is not the ride height, but instead the height of the wheelwell.

 

The difference is ride quality is minimal. On the highway it's actually better. On slower roadways (sub 40mph) with undulations, the suspension is fractionally more bouncy. The ride height is the same because of the stiffer rate of the Z spring.

 

You may notice they will settle a little with time. I never had coupe springs, but the 350Z springs are now .25-.5 inch lower than when they were initially mounted on my sedan.

 

I thought the rate got stiffer on the 05 up coupe rears.

I definately don't want that. I just don't like how uneven the car looks.

Everything your saying is promising. I can't wait to do mine. The only difference is that I have a full Z susp w/ shocks/stuts. I wonder how different it will feel from yours.

Thanks for the info, sharing and contribution!