It’s a question that still echoes in motorsport circles: how could such a large, grounded machine suddenly take flight? The sight of a Mercedes-Benz CLR flipping through the air at Le Mans in 1999 was, to put it mildly, a “what-the-fuck” moment. For those accustomed to cars firmly planted in two dimensions, witnessing one unexpectedly embrace the third was utterly counterintuitive and shocking. I recall being at the 1998 Petit Le Mans, working for Downing/Atlanta, when the Porsche GT-98 flips were replayed. Even that, while dramatic, didn’t quite prepare anyone for what was to come at Le Mans. Years ago, online discussions, particularly on forums like 10-10ths, floated theories about tire failures contributing to the CLR accidents. However, that inquiry, much like then, is spurious. The real culprits lie deeper, rooted in the car’s very design. Over time, I’ve compiled my thoughts on the true factors behind these incidents, expanding on an old response to that tire question. This analysis, once buried on my hard drive, deserves to be shared to shed light on the aerodynamic mysteries behind the “Flying Mercedes” of Le Mans.
Mercedes Benz CLR race car design blueprint
The core issues plaguing the Mercedes-Benz CLR can be traced back to its fundamental dimensional architecture, a deficit in overall downforce, and ultimately, a cruel twist of fate. Designed to maximize the regulations, the CLR stretched the limits with an overall length of 4890 mm. Its wheelbase measured 2670 mm, paired with a substantial 1080 mm front overhang and an even more pronounced 1140 mm rear overhang.
The 1997 regulations by the ACO allowed LMP and LMGTP cars with flat bottoms to incorporate a rear diffuser, starting from the rear wheel centerline. Crucially, designers had considerable freedom in defining the diffuser’s trailing edge, only constrained by the bodywork’s end. Mercedes exploited this, pushing the CLR’s rear diffuser and bodywork significantly further back than any competitor. To illustrate, the Toyota GT-One featured a 990 mm rear overhang, the Audi R8C 940 mm, and the Nissan R391 a mere 880 mm, dwarfed by the CLR’s expansive 1140 mm. At the front, the CLR’s 1080 mm overhang was within the norm, perhaps leaning towards the longer side. However, the front diffuser was notably small and subdued, especially when juxtaposed with the more aggressive designs of the Toyota GT-One or even the BMW LMR. Sandwiched between these long overhangs was the shortest wheelbase in the LMP category, at 2670 mm. Le Mans prototypes typically favor longer wheelbases for enhanced aerodynamic stability; the Toyota GT-One boasted a 2850 mm wheelbase, the Audi R8C 2700 mm, and the BMW LMR 2790 mm. None of the CLR’s rivals combined such a short wheelbase with such extensive overhangs, both front and rear.
This unique dimensional recipe created an exceptionally sensitive aerodynamic platform. A shorter wheelbase amplifies the effect of pitch changes. Imagine the car braking or accelerating; the narrow wheelbase translates even minor shifts in weight distribution into significant alterations in ride height at the extreme ends of those lengthy overhangs. Reports of the CLRs porpoising on various sections of the track throughout the Le Mans weekend strongly suggest an inherent instability in the car’s aerodynamic foundation.
Adding to this precarious balance was the coupe bodywork. The very shape of a closed cockpit can contribute to aerodynamic lift, a force that must be actively counteracted by the car’s downforce generation. While virtually all race cars in this class are designed to generate substantial downforce, usually enough to negate the lift from the cockpit, it remains a factor. Designers constantly navigate this compromise, weighing the lift against the drag reduction benefits that a closed-top car offers.
Anecdotal accounts suggest the CLR team opted for soft rear springs. While this remains unconfirmed, if true, it would be another element compounding the CLR’s vulnerability at Le Mans in 1999. Soft rear springs are sometimes employed on high-speed circuits to enhance straight-line speed. At speed, the downforce generated at the rear compresses the softer springs, lowering the car’s rear ride height and thus reducing overall drag for better top speed. However, this setup can further destabilize the car under pitch changes.
Following the practice and morning warm-up incidents, the Mercedes team sought counsel from Formula 1 aerodynamicist Adrian Newey in a frantic search for solutions. The potential consequences of another crash were stark. If a CLR were to crash again, the damage could be catastrophic. Any injuries would have serious repercussions, potentially involving legal ramifications similar to those requiring a car accident lawyer in San Diego after road traffic incidents. One of the immediate measures proposed and implemented was the addition of front nose dive planes to generate some supplementary front downforce. Both CLRs started the race with these dive planes fitted. It’s crucial to remember that cars of this era, especially in Le Mans trim, generally ran with relatively low downforce levels compared to modern prototypes. Data from the open-top Nissan R391 LMP900 of the same period indicates downforce levels between 2000-2500 lbs at 200 mph.
Intriguingly, in a press release issued after the warm-up crash, Mercedes-Benz, aiming to reassure everyone about the cars’ race viability, stated that these dive planes would add as much as 25% more front downforce. If we assume a baseline of 2000 lbs of total downforce with a 45/55 front/rear split (900 lbs front), a 25% increase translates to an additional 225 lbs of front downforce – a plausible figure. Rebalancing the split to 45/55 with this addition could theoretically increase total downforce by as much as 500 lbs. However, the fundamental issue remained: the cars racing in this era, including the CLR, operated with comparatively limited aerodynamic downforce, leaving little margin for error.
Finally, we arrive at the “moment” of the crashes. To understand why the “flying Mercedes” incidents occurred, we need to synthesize these contributing factors. Lacking firsthand observation of every detail, my analysis will rely on generalizations. In most, if not all, instances, the CLR was following closely behind another car. This immediately reduces downforce on the following car’s nose due to turbulent air (dirty air) from the lead car. Simultaneously, the CLR appeared to be undergoing a change in “attitude,” perhaps cresting an undulation in the track surface or running over a curb. Something was altering the car’s pitch, even subtly, triggering a sudden, yet potentially small, shift in aerodynamic forces.
Let’s piece it together: downforce is already diminished at the front due to turbulent air from the car ahead. The CLR’s pitch changes because of track variations, further decreasing front downforce. The CLR’s design, with its long overhangs and short wheelbase, makes it exceptionally sensitive to these pitch changes, resulting in a more pronounced downforce fluctuation than its competitors might experience. These combined factors lead to a significant and rapid loss of front downforce. As the low-pressure zone under the CLR’s nose weakens and approaches zero, the inherent lift generated by the coupe cockpit and the upper bodywork begins to assert itself, lifting the nose even further. Meanwhile, the rear wing continues to function effectively, firmly planting the rear of the car and creating a pivot point around the rear wheel centerline. As the nose ascends, the rear diffuser, extending far beyond the rear wheels, gets closer to the track surface. Paradoxically, this proximity initially increases rear downforce, further exacerbating the pitch-up motion and acting as a lever to amplify the lift at the front. At this point, the underside of the car becomes exposed to the airflow. The lift generated by the cockpit and now acting on the face of the exposed underfloor completely overwhelms any remaining downforce. The “flying Mercedes” is no longer a car; it’s become an aircraft, taking off in a truly dramatic and unexpected fashion.
The ultimate irony was the immense pressure to perform. So high were the stakes, and so significant the investment, that Mercedes-Benz chose not to withdraw the remaining cars even after the second airborne incident in morning warm-up. I’ve often pondered if there were more incidents than the widely documented three. Rumors circulated at the time about a similar occurrence during testing, though these were never substantiated. In the years since, Mercedes has seemingly opted to erase the entire episode from its corporate memory, along with much of its Le Mans history. It seems highly unlikely we will ever witness their return to the Circuit de la Sarthe.
