This is a photo of the roll cage construction in the very successful Nissan Primera which was built for the BTCC 1998 season.
There are some interesting things to note if one looks carefully:
• The Primera used MacPherson struts at all four corners in 1998. They have since been forced to revert to a beam axle in the rear for the 1999 season because the Japanese version 4wd suspension clause ran out. Check out the reinforcement of the front strut towers - amazing.
• Although the rules limit the amount of fender mod's allowed (almost nothing in 1998) check out the way they re-fabricated the front inner wheel wells in order to cram those 19" wheels under there.
• Note that they DO employ a diagonal tube in the main hoop. But no harness bar and no seat brace (the driver sits on the right).
• Look at the way the cage ties into EVERY rear suspension pickup.
• Note the tubes running just below the A-Pillars. They go straight from the dash area to above the driver's head - no bends. They also use the standard forward bars tucked into the A-Pillars but they are difficult to see in this picture. The straight tubes feed the loads from the front suspension straight into the back of the cage. Because they are straight, the load path is direct and the tubes do not bend under compression.
• This picture is from "Racecar Engineering". An English publication which can be obtained in the States if you scratch around a bit.