[Wavey]

Originally Posted by KTL

Yes there is legitimate concern by removing the original bumpers and replacing with fiberglass or polyurethane. The original bumpers have impact absorbing shocks (USA cars) or crush tubes which attach the bumpers to the chassis tub. So a light impact to the aluminum bumpers provides some energy absorption and impact protection.

The fiberglass bumpers are a do-it-yourself figure out how to attach them. Do a search on the forum and you'll see all sorts of methods people have come up with to fasten them to the car. What that means is the fiberglass basically forgoes any crash protection and therefore an impact is going to get transferred directly to the chassis wherever the point of impact is at. That said, these cars get bent pretty good in a crash, even with the original bumpers in place

Folks have made their own "nerf bars" from scratch to provide some semblance of structure behind the fiberglass. But it's still a far cry from the original design. And the original design isn't exactly super high tech, which is rather caveman- like compared to the crash protection of more modern cars. Even the 964 body is leaps and bounds ahead of the old 911 crash worthiness.

Like KTL says, once all the OEM bumper parts have been removed, you can fabricate a steel "nerf bar" that bolts to the original bumper shock holes in the tub, and it sits inside the new FG bumper. Some impact protection but not a lot. This works for the front and rear. The FG bumper itself is a pretty rigid box structure once it's bolted to the tub and fenders. It can be bolted to both using the original holes at the front of the tub, and the holes at the bottom front of the fenders where the accordion pieces used to mount. It's actually really sturdy that way, doesn't need any bolts or brackets through the front face or along the bottom.