I have experimented with coilover spring rates on a couple of zeds and these are my findings so far. On the blue car with GAZ suspension I originally went for 350lb fronts and 300lb rears. People told me the rear felt a bit soft on the track so I changed the rear to match the fronts at 350lb. This made a noticeable difference and the car felt very neutral in its handling. It should be noted that the car weight is 602kg front and back with 30lt of fuel. On the red 260z I had Fourways sectioned struts and the car sat too low at the back and felt soft. I increased the rear spring rate to 250lb, same as front, and raised the rear ride height. This also improved the feel and general ride quality. In my opinion this is the perfect road setup for the heavier 260z. On the silver car I have just swapped out the standard suspension for BC racing coilovers with 4kg(224lb) front and 5kg(280kg) rears. This is the BC recommended springs for a road/track car. The car feels a bit bumpy on the back and I don't think there is sufficient weight in the rear of the car for this weight of spring. I'm considering going down to a 4.5kg(252lb) spring. I'm looking for advice on this as I'm no expert but do have some experience as above. Why do they recommend a stiffer rear spring on a car that weighs less at the rear? What am I missing?