Upgrading a Mercedes for rally racing presents unique challenges, especially when installing a roll cage while aiming to retain some of the vehicle’s original architecture. A key decision revolves around preserving the rear firewall, converting to coil-over suspension, and potentially keeping the factory fuel tank. This article explores the options and considerations for installing a robust roll cage in a Mercedes Rally Car, focusing on maintaining safety without unnecessary modifications.
Option 1: Retaining the Stock Fuel Tank and Firewall
The Mercedes’ original design features a nearly sealed rear firewall, with the fuel tank positioned upright behind the rear seat. Regulations permit the stock tank as long as a fire-resistant shield separates it from the passenger compartment. Keeping the original fuel tank offers several benefits. It reduces build costs, leverages the tank’s robust factory location, and simplifies fuel pump maintenance. The factory tank’s location, while generally safe, does place it technically outside the main roll cage structure, increasing potential damage risk in severe impacts. Despite this, many race cars successfully utilize factory tanks without issues, but the risk, however small, remains.
Option 2: Coil-over Conversion and Firewall Modification for Enhanced Safety
Converting to coil-over suspension requires widening and reinforcing the rear shock towers. This process becomes simpler when integrated with the roll cage structure. Running the rear down-bars through the firewall and attaching them to reinforced shock mounts would provide significant structural rigidity. However, this approach necessitates removing the possibility of using the factory fuel tank. While a fuel cell in the trunk becomes an option, it might lead to eliminating the rear firewall altogether. Positioning a fuel cell lower and behind the driver’s seats (within a protective metal box) improves the center of gravity and reduces weight. Moving the fuel cell inside the safety cell enhances safety, but adds considerable expense to the build, requiring a careful cost-benefit analysis.
Option 3: Compromise with Angled Down Bars
A potential middle ground involves angling the rear down bars to narrowly bypass the fuel tank. An X-brace for these bars could then terminate at the firewall. However, this configuration might violate FIA regulations, which dictate roll cage construction standards. Thoroughly reviewing the FIA rulebook is crucial to confirm the legality of this approach. This option seeks to balance retaining the fuel tank with cage integration but introduces regulatory uncertainty.
Option 4: Independent Rear Cage Structure and Strut Tower Reinforcement
Another approach is to terminate the rear down bars on the interior side of the rear firewall, attaching them to the wheel well sheet metal. Subsequently, a “free-standing” mini-cage could be constructed in the rear to brace the rear shock towers to the floor, rear firewall, and other suitable points. This packaging-friendly option might present a higher risk of failure in the fabricated strut tower supports. Careful engineering and robust construction are essential to ensure the modified strut towers can withstand rally conditions. Reinforcing these areas with additional bars connecting to the trunk floor and upper sections, potentially tying the towers with a removable bar, could enhance structural integrity. Sheet metal of various gauges can also be used to further strengthen the towers.
Conclusion: Weighing Options for Your Mercedes Rally Build
Deciding on the best roll cage installation for a Mercedes rally car requires careful consideration of safety, budget, and desired vehicle modifications. Each option—retaining the stock tank, modifying the firewall, compromising with angled bars, or building an independent rear cage—presents distinct advantages and disadvantages. Ultimately, the optimal solution depends on individual priorities and a thorough assessment of the specific Mercedes model and intended rally use. Consulting FIA regulations and experienced roll cage fabricators is highly recommended to ensure a safe and compliant build.
