Perhaps m4a1mustang is going by the GVWR tag on the driver's door. On my '11, it states that the maximum passenger + cargo load is 432 lbs.

So, 600lbs in the trunk + driver + fuel = a seriously overloaded Z, according to Nissan. No doubt that much weight helps traction. I offer no opinion as to how that affects one's car, but you are almost doubling the "official" capacity with a ~780lb load of concrete and driver.

I don't disagree at all with the Nissan recommended use. As I always try to remind people, 'don't always use the advice in forums' for their own application. I don't believe I would EVER drop 600lbs in my car either. Putting in 4-6 bags is just a really heavy passenger (unless you can find a really big friend to ride with you). I actually agree with m4a1 on the 'potential' to ruin a Z. I just see it happening driving in the conditions and the actual ratings of the stock suspension in the Z. If you slide into a curb, even at a safe speed -10mph) with all that weight, however, that would be a blown axle for certain.

The idea is to get weight towards the rear of the car and to increase the pressure per inch of contact. Even 240lbs is better than none. It's the same reason trucks have cinder blocks/bags of sand/concrete in their beds in the winter.

You lack skill.

your a herb