BGTV8

Lowering the car lowers the CoG to improve mechanical grip.

If you have a splitter/flat-floor/diffuser then you'll get some down-force, but the underside of a Z34 is pretty dirty from an aero perspective, so we are really limited to splitter and wing and that is really about killing hi-speed lift than anything else.

In terms of the amount of bump and droop, I would not go any lower than 55-60mm of bump and that implies a front wheel rate of 400 lbs/in as a minimum (this is about 2.5 times the OEM Z34 wheel rate).

Because I like to run the rear a bit softer, you'll need some rake on the car, but beware roll-centre height differences that are more than 6-8".

This can be difficult to do with OEM suspension, and unless all the bushes are changed for solid (heim joints or - say- delrin bushes), it will all be moot in any event.

You do not want your car to hit the bump stops under braking (will trigger the ABS or provoke a lock-up), or in roll (in roll the spring rate rises dramatically depending on bump-stop material) and the will cause understeer at front or oversteer at the rear if it happens - and it will be dramatic !! If the corner is bumpy and you are a millimetre off the bump-stop, then hitting a bump can be the difference between a dynamite corner entry/exit and the car flinging itself at the scenery with zero time to catch it.

This is one reason why I run 18" wheels with small diameter (645mm-650mm) tyres because I get a free CoG drop of 25mm and the suspension angles remain (near-enough) to OEM settings.

However, a car setup for the track will not be a pleasant daily drive or even road drive as it will be too stiff to counter low ride height, have no compliance, follow tracks in the asphalt and generally be a PITA.

Tread your own path.

RB