Why are windscreens so important at the 24 Hours of Le Mans?

Visibility is a key factor at the 24 Hours of Le Mans, a race in which changes in light (day, night, dawn and dusk) and the changing weather, add to the dirt that cars accumulate over such a long event.

This weekend the 24 Hours of Le Mans take place, one of the most legendary events in world motorsport. In this article we want to explain the differences between the windscreens of a road car and those of the cars taking part in this event. Visibility is a key factor at the 24 Hours of Le Mans, a race in which changes in light (day, night, dawn and dusk) and the changing weather, add to the dirt that cars accumulate over such a long event.

Laminated glass vs polycarbonate

The first difference is the composition: a road car fits a rigid laminated glass windscreen, whereas in competition polycarbonate is used for all the windows. The main reason is weight saving, which can reach 50%. The other advantage it offers is superior impact resistance. This material cannot be used in the windscreens of road cars for three fundamental reasons. The first is its lack of rigidity. A glass windscreen contributes up to 30% of the structural strength of the vehicle in the event of a rollover. Because competition cars incorporate a safety roll cage, which prevents the roof from caving in, they do not need that additional rigidity.

Its second disadvantage is that it scratches very easily, clouding visibility and causing annoying reflections; drivers would have to replace it frequently. The third reason is that it is less transparent than glass and offers a poorer quality of vision. Finally, aspects related to its fitting make it more difficult to achieve a perfect seal with polycarbonate.

The challenge of keeping the windscreen clean

Competition cars leave a lot of dirt on the track, from rubber particles shed by their tyres and from oil and other fluids. Many of these elements end up stuck to the windscreen of the car behind, since in racing there is no need to keep a safe distance. To maintain the best possible visibility throughout the 24 hours of the race, the mechanics thoroughly clean the windscreen at every pit stop (roughly every 40 minutes) with powerful cleaning products.

But dirt becomes so embedded because of the speeds reached at Le Mans that this is sometimes not enough. For this reason, thin translucent plastic sheets are fitted over the windscreen, which are removed as they can no longer be cleaned, as the race progresses. The winner of last year’s edition had eleven sheets fitted, and this is the maximum number usually used, since beyond that the image becomes distorted and the driver’s visibility is compromised.

The windscreen wipers also present many challenges. In competition they are usually single-arm, to reduce aerodynamic drag and because it is not as necessary, as on the road, for their sweep to reach every corner. Drivers must be careful when operating them, since if the windscreen is heavily soiled, using them can make the situation worse rather than better. And being left with a smeared windscreen in the middle of a race with the sun in your face is not a good idea.

The importance of the windscreen for road safety

The windscreen plays a key role in road safety, first of all because of its obvious implications for correct visibility at the wheel: 90% of the information we receive while driving reaches us through sight. Just as important, the windscreen contributes up to 30% of the vehicle’s structural strength and is a key element in preventing the roof from collapsing in the event of a rollover. In addition, the effectiveness of the passenger airbag depends on the good condition of the windscreen, since when it deploys it rests against the glass, exerting great pressure that could even tear it out. Finally, the sensors of ADAS safety systems are usually mounted on the windscreen.

For all these reasons it is very important to carry out correct windscreen maintenance. And on cars equipped with ADAS safety systems, correct recalibration is required after replacement: when the windscreen of a car equipped with ADAS safety systems is replaced, the cameras and sensors must be recalibrated using special software and tooling.

Source: Carglass