The E46 cage is notable in that BMW moves away from extending the roll cage all the way back to the top of the C-pillars (as was the case on the late E30 and all E36 factory cages). A very unique feature are the twin buttresses extending down from mid-roof to the dash. These buttresses first appear to be "double front down bars" with a large perforated gusset connecting the two. However, BMW enthusiast Kurt Johnson, who has examined one of these cages up close, points out that the design is actually standard downtubes tucked into the A-pillars with a thin, bent sheet metal gusset forming the rest of the buttresses. Certainly a very light and rigid layout.

The rear part of the cage is now quite conventional in design. This is especially true in light of the previous E36 factory roll cage, which had a very complex rear layout. It is a fact that the factory "road" chassis on modern cars is becoming ever stiffer, and it is thus likely that cage designers have come to rely more on this inherent rigidity of the bare shell in contributing to overall race car chassis stiffness. Also, as pointed out by K. Johnson (based on conversations with PTG), the rear of the Motorsport cage is purposely kept simple to allow the end-user to customize it according to the specific rules of the racing series in question. This eliminates the need for BMW Motorsport to make several different types of cages for the various racing series around the globe (as was the case with the E36 chassis).