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We did get a good look at the chassis. The chassis starts off as a standard M3 body in white pulled right off BMW’s assembly line. All excess sheet metal is removed and the chassis is reinforced with an all inclusive roll cage that ties the whole structure together providing chassis stiffness as well as protection for the driver in a semi tube frame cradle. Chassis stiffness is very important as it is a huge aid in suspension tuning. A flexing chassis is analogous to an undamped spring which creates tire shock and renders adjustments to the suspension ineffective. At a total weight of 2,535 lbs, the big BMW is surprisingly light. For instance that weight is about the same as our Project Spec-V Time Attack car which is much smaller in comparison.
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| The cage ties the whole car together from the center driver protection zone, to the suspension pick up points in the trunk, through the firewall into the front shock towers to the front of the car. The BMW is a semi tube frame car. |
The doors, hood, trunk lid and roof are all replaced with lightweight dry carbon parts. The doors have a Kevlar and foam impact attenuator built into them that butts against the roll cage for safety in side impact. A unique feature of the chassis is the safety roof. In the event of a serious crash, the M3’s carbon roof can be easily peeled away and the upper part of the cage removed with simple tools. The driver’s seat is a containment structure made of carbon fiber and it is designed to support and protect the driver much like a helmet. Once the roof is removed and the cage dismantled, the seat can be removed via quick release fasteners and lifted through the roof with the driver strapped safely in place. The injured driver can actually be transported to the hospital in the seat.
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| The suspension uses Ohlins 4-way adjustable shocks with through shaft technology. The unequal length A arm suspension members are fabricated and are quite different from the strut front multilink rear stock BMW. |
We were not allowed to look too closely under the car but we were able to glean some information about the suspension. The front suspension appears to be close to conventional with aero profiled tubing fabricated control arms and the front suspension’s pick up points have to remain within 20mm of stock. The rear suspension looks to have been converted from the standard BMW multilink to unequal length A arms with the pick up points on the tranaxle casing like most prototypes. These variations from the production car have to be approved in the car’s homologation with ALMS.
