What you have in most Jeeps, YJ, TJ, and JK is a sport bar, not a roll bar, the bar that drops verticaly next to the seat is the only bar that comes near the frame, and that only by proximity of a body mount, the rear bar bolts to the tub above the tail lights, and even worse, the front bars bolt to the windshield frame. In a rollover accident, the one bar next to the seat will offer some protection so long as you roll directly to the side and dont still have forward momentum to make that one bar fold, the rear bar will also afford a modicum of protection in a minimal way but again, only as long as the main bar doesnt fold, the windshield bars will protect you just as much as the winshield frame, that is that bars only support.
There are some very good aftermarket "sport cages", most are prohibitively expensive, you can buy sport cages that attach to the pillar system at the dash board, this is better than the windshield, but only just, you can also buy aftermarket frame tie-ins for your existing cage.
This feels like a safety issue, what you have to remember is that Dept of Trans has standards for roll over safety, its mostly based on a per vehicle basis on weight, so bigger tires, bumpers, sliders, all this adds weight Jeep didnt engineer for, luckily it isnt necessarily that much weight, and you can bolster your cage with some relatively affordable additions. Hardrock 4x4 makes a nice cage for about $600, I got mine on amazon for $290
Amazon.com: Performance Accessories 82200BB Bicycle Black Finish Sport Cage: Automotive (two of the pics on amazon are of my Jeep, topless so you can see it very well).
Sport and roll cages are like the old saying about driving and safety, 50mph is safer than 75 mph, but 30 mph is safer than 50mph, but the only way to be really safe is dont get in the car, same with cages, mine is a little safer than stock, not as safe as a full custom, but the only way to be safe is dont flop your Jeep
hope some of this helps.
