I finally decided to get a roll cage for my 535is, although all I had time for was the 4 point bar. The front of the cage will be installed eventually. My fabricator used 1-3/4" x .120 wall tubing for the main hoop, diagonal, harness bar, and rear legs. BMWCCA clubracing rules allow .095 wall, but I did not want to skimp on strength to save 20 lbs in the rear part of the cage. I'll use 1-5/8 x .095 for the front half for weight savings and cockpit clearance. I'll be able to reinstall the rear seat, although it won't be fit for human occupancy. I'd like to thank KH, my fabricator, for doing great work on such short notice.
Here are more pictures on the rollbar.
Here is the back of KH's head while welding the right rear bar to the main hoop assembly. A piece of sheetmetal and a wet rag insulate the headliner from heat and sparks.
The main hoop assembly consists of the main hoop, the diagonal, and a horizontal harness bar. The assembly was tacked outside the car then temporarily installed to check fit. We pulled it out of the car to finish welding. There are advantages to driving a four-door!
If you doubt the necessity of a rollbar because you only attend a few driver schools a year and don't go that fast, look at the photo at the bottom of this page. It was a stock 325e running in the intermediate run group. The driver and instructor were shaken and bruised but essentially uninjured. I was two cars behind it on the diving turn at Lime Rock Park. Yes, that is the front passenger seat headrest sticking out the back window