Frame Stiffening & Roll Bars

[splinter]

I the recent discussions on roll bars, there seems to be a feeling that this results in a pretty rigid frame (depending on mounting points and full cage, etc.). For those of you who have them, do you feel that this provides enough rigidity or is the frame reinforcement kit still necessary?

[Bobbitt]

I am still in the middle of putting my car back together, but I don't see how a bolt in cage will give you the stiffness you need. The bolt in cages only marginally stiffens the cockpit. I say marginally, because it ties into the floor does not tie into the A-pillars at all, so the car can flex around the front of the cage. My cage does tie into the firewall, so that helps some.

The weld in stiffening kit is for around the rear suspension. It helps to keep the suspension in place and also helps to prevent the sheet metal from tearing under high cornering loads. I had the stiffening kit welded in in addition to the cage.

I also fabricated a stiffening kit to support the inner trailing arm mounting ears. I have know of 2 cars having those rip off due to cornering loads. The cars were rust free, so that was not an issue. All I did was bend up some sheet metal to cover the engine side of the ears. Some weld holes were drilled in it so there would be more weld contact with the base metal.

There is also a bolt or weld in bar that goes under the rocker panels. It attaches at each end of the rockers and helps add stiffness. The people that I know who have installed them swear by them. I am not adding them now, but it should be an easy retrofit later.

[halbl]

The roll bar I installed bolted to a plate welded to the longitudinal frame, not the floor. After adding the stiffening kit,(all the pieces and a tough job even on a rotisserie type device) the door sag was slight but noticeable. After adding the roll bar the door sag was virtually gone. I recommend the stiffening kit first. I've heard a lot about the "clamshell" design stiffening kits but have no experience. They come in different gauges of metal and fit. On the other hand I have a '75 driver with battery tray shot and the floor pans in terrible shape, but no door sag. We have a fun autoX next weekend and I plan to ask an expert to drive and evaluate based on his 20+ years experience. Will report back.

[Bobbitt]

halbl was correct - the roll cage ties into the longitudinals, not the floor.