The Mercedes-Benz CLR. Just the name evokes a sense of awe and, for many motorsport enthusiasts, a lingering question: “What exactly happened at Le Mans in 1999?” It was a truly bewildering moment when this substantial machine, typically confined to the two dimensions of the track, suddenly defied expectations and ascended into the third dimension. For those present at the 1998 Petit Le Mans, including myself then working for Downing/Atlanta, the replay of Porsche GT-98s flipping on the pit lane TVs was met with audible gasps. Years later, online inquiries persist, often misguidedly pointing to tires as the culprit behind the CLR’s dramatic airborne incidents. This notion is as inaccurate now as it was then.
Seeking to clarify the situation, I previously offered an explanation, outlining what I believed were the true contributing factors to these unforgettable events. This response, initially penned on 10-10ths, served as the foundation for a more detailed analysis that has evolved over time. Lost on my hard drive until recently, I felt compelled to share this expanded perspective online, hoping to shed light on the real reasons behind the Mercedes Clr’s Le Mans misfortunes.
In my expert opinion, the root causes of the CLR’s issues can be traced back to its fundamental dimensional architecture, a deficiency in overall downforce, and ultimately, a confluence of unfortunate circumstances.
Let’s delve into the specifics of the Mercedes CLR’s design. It was engineered to the maximum permissible overall length of 4890 mm. Its wheelbase measured 2670 mm, complemented by a front overhang of 1080 mm and a rear overhang of 1140 mm.
1999 Mercedes Benz CLR
Alt text: Side view of the 1999 Mercedes Benz CLR race car highlighting its long rear overhang, crucial for understanding its aerodynamic characteristics at Le Mans.
A significant rule change in 1997 by the ACO allowed flat-bottom LMP and LMGTP cars to incorporate a rear diffuser extending from the rear wheel centerline. Crucially, the regulations granted designers freedom to define the diffuser’s trailing point, provided it aligned with the bodywork’s end. On the CLR, this rear diffuser was exceptionally pronounced, far more so than on its contemporaries. Consider the rear overhang comparisons: Toyota GT-One at 990 mm, Audi R8C at 940 mm, Nissan R391 at 880 mm, all dwarfed by the CLR’s substantial 1140 mm. The CLR’s front overhang, at 1080 mm, was within the range of its rivals, though leaning towards the longer side. However, the front diffuser underneath was notably smaller and less aggressive compared to designs like the Toyota GT-One or even the BMW LMR. Sandwiched in the middle of these dimensional choices was a 2670 mm wheelbase. Le Mans prototypes typically favor longer wheelbases for enhanced aerodynamic stability. Yet, the CLR possessed the shortest wheelbase within the entire LMP category. In stark contrast, the Toyota GT-One boasted a 2850 mm wheelbase, the Audi R8C 2700 mm, and the BMW LMR 2790 mm. Compounding this, none of the CLR’s competitors exhibited such extensive front and rear overhangs.
This unique architectural configuration resulted in a highly sensitive aerodynamic platform. Even slight alterations in the car’s attitude, induced by braking or acceleration on that short wheelbase, could translate into significant ride height variations at the extreme ends of those lengthy overhangs. Reports of the CLRs porpoising across various track sections throughout the Le Mans weekend strongly suggest an inherent instability within the aero platform.
Adding to this complexity was the car’s coupe bodywork. The cockpit shape of a closed-top car inherently contributes to lift generation, a force that the car’s downforce must actively counteract. While most race cars in this class generate substantial downforce to overcome this negative effect, the cockpit bubble remains a factor. Designers typically navigate this trade-off, balancing the lift with the drag reduction benefits offered by a closed-top design.
Anecdotal evidence suggests that the CLR was also configured with soft rear springs. While this remains unconfirmed, if accurate, it would further exacerbate the factors working against the CLR during those critical moments at Le Mans in 1999. Soft rear springs are sometimes employed on high-speed circuits to enhance straight-line speed. At elevated velocities, the downforce generated at the rear effectively compresses the rear suspension, reducing the car’s overall drag and enabling higher top speeds.
Furthermore, between the practice and morning warm-up incidents leading up to the race, the Mercedes team reportedly sought consultation with Formula 1 aerodynamicist Adrian Newey to devise a solution. Recognizing the potential for catastrophic consequences in a high-speed incident, and the importance of safety (underscored by the need for resources like car accident lawyers in San Diego should a crash occur with injuries), one proposed remedy was the addition of front nose dive planes to increase front downforce. Both CLRs commenced the race with these modifications. It’s crucial to remember that cars of this era generally operated with relatively low downforce levels, particularly in Le Mans trim. Data from the open-top Nissan R391 LMP900 (data source) indicates downforce levels between 2000-2500 lbs at 200 mph.
Intriguingly, in a post-warm-up crash press release aimed at reassuring the viability of their cars for the race, Mercedes-Benz stated that these newly added dive planes would contribute as much as 25% additional front downforce. Assuming a baseline downforce of 2000 lbs with a 45/55 front/rear split (900 lbs front), a 25% increase translates to 225 lbs of added front downforce. Rebalancing to a 45/55 split would then suggest an overall downforce increase of approximately 500 lbs. However, this underscores the fundamental point: the cars racing in this period simply had limited aerodynamic downforce by modern standards.
Now, let’s reconstruct the pivotal “moment.” By synthesizing these contributing factors, along with a few others, we can understand the sequence of events. Lacking direct observation of each incident, my analysis relies on generalizations. In most instances, it appears the CLR was following closely behind another car. This proximity would undoubtedly diminish downforce at the CLR’s nose due to turbulent air. Simultaneously, the CLR was likely experiencing a change in “attitude,” perhaps cresting a track undulation or running over a curb. Any slight shift in the car’s disposition could trigger a sudden (though initially minor) change in aerodynamic forces.
Alt text: Dramatic image capturing the Mercedes CLR airborne during the 1999 Le Mans race, emphasizing the severity of the aerodynamic lift issue that led to multiple crashes.
Therefore, the sequence unfolds as follows: downforce reduction at the front of the CLR due to turbulent air from a leading car; a change in pitch caused by track variations, further exacerbating downforce loss; the CLR’s heightened pitch sensitivity due to its long overhangs and short wheelbase amplifying these effects, leading to a more substantial than anticipated downforce fluctuation. As the low-pressure zone beneath the CLR’s front approaches zero, the lift generated by the cockpit and upper bodywork begins to dominate, further elevating the nose. Meanwhile, the rear wing continues to function effectively, firmly planting the rear wheels and acting as a pivot point around the rear wheel centerline. As the nose lifts, the rear diffuser, extending significantly beyond the rear wheel centerline, draws closer to the track surface, ironically generating even more downforce at the rear, further intensifying the lifting effect at the front. By this stage, the underside of the car becomes exposed, and the combined lift forces from the cockpit and the exposed underfloor completely overwhelm the car, resulting in a dramatic airborne episode.
Ironically, the immense stakes associated with failure compelled Mercedes-Benz to persevere with the cars even after the second incident in morning warm-up. I’ve often wondered if the three publicly documented incidents were truly the extent of the problem. Rumors of a prior incident during testing circulated at the time, though they never gained substantial traction. In the years since, Mercedes has seemingly chosen to erase the incident from its memory, and indeed, perhaps even their broader Le Mans history. It appears increasingly unlikely that we will ever witness their return to the Circuit de la Sarthe.
