This a very hot topic. And as a track day participant, one I continuously watch through the various forums etc.

There is much to be said for the all or nothing mentality with safety equipment. That is get a full roll cage, six point harness and only drive the car with a helmet. This isn't necessarily practical so some guidelines have to be thought about.

1. If you have harness that will not allow your body/torso/head to duck in the event of a roll over, then make sure you have a roll bar to prevent the cave in of the roof snapping your neck.

2. If you have a roll cage/bar then wear a helmet at all times unless there is no way your head can contact it in the event of a collision.

There is also much debate over 4/5 and 6 point harnesses.

In early 911s i've seen roll bars that seem to be far enough out of the way that a collision with the head can't happen, so I would make sure that this is what you are using in a street driven car. Otherwise don't bother and by the same token don't use a harness.

I am also looking at putting a roll bar in one of my early cars, but more for looks than anything as I really have no intention of agressively tracking the car. But more than likely I won't bother

My track car of choice is a modded Subaru WRX STi. I do use a harness bar and a four point harness on track. The Subaru has standard integral rollover protection that makes me comfortable using the harness. The four point provides similar anti submarining action to a 3 point if adjusted properly (another issue) and keeps me in place while driving "spiritedly". I've thought about caging this car but then it wouldn't be usable as a daily driver. I certainly wouldn't want my kids in the car with any metal cage near them. I of course wear a helmet on track too.

Just something to think about.