To continue our series on the technical aspects of the Le Mans 24 hours race we could do no better than refer to the significant braking partner to many on the grid, Brembo Brakes. Here we have reproduced (with thanks) their article making a detailed comparison between the performance of brakes in LMP1 and Formula 1. These two FIA Championships have in recent years vied for the pinnacle of motorsport accolade. It is clear from this analysis that there are twin peaks to be considered in our sport, different attributes, strategies and performance is extolled and valued and the two clearly can go exist.
Sit back, grab a cold one and consider the relative braking performances and marvel at what a driver has to do lap after lap, hour after hour.
For half a century, Formula 1 races and the 24 Hours of Le Mans have been the world’s two most important competitions for four-wheeled single-seaters and prototypes. The hefty investments made by Manufacturers in recent years have resulted in equipping these cars with in the region of 1,000 horsepower hybrid engines.
For the FIA World Endurance Championship(WEC) and Le Mans, the Manufacturers have quite a bit of choice in the construction of the power units. Some have focused on 2L twin-turbo engines with kinetic energy recovery, while others look towards a simple naturally aspirated 4.5L engine (regulations set the maximum to 5.5L). In Formula 1, there is a lot of intense deceleration where the values often surpass 5G (at Monza even up to 6.7 G), but at the 24 Hours of Le Mans, the braking force does not go over 3.5 G.
The reason for this wide gap is the difference in mass of the different cars. A Formula 1 single-seater has a minimum weight of 735kg including the driver while an LMP1 car racing at Le Mans weighs at least 875kg, plus 3kg for camera gear or a spare power pack. Of course, non-hybrid LMP1 cars can weigh up to 45 kg less, which means the overall weight drops to 830kg.
THE DIFFERENCE BETWEEN 100 MINUTES AND 24 HOURS RACES
Formula 1 races last about 100 minutes, and are limited to 2 hours. Le Mans lasts an entire day/night cycle of 24-gruelling hours. So, it is better to compare two tracks that are similar in length, number of corners, geographic position and climate.
During the Belgian GP in Spa, the Formula 1 single-seaters have to face about 350 braking sections, while at the 24 Hours of Le Mans, an LMP1 will brake more than 4,000 times.
This is a huge challenge for Brembo. Fortunately, the Company has gained 20 years of experience in endurance racing and has developed tailor-made solutions.
The only common factor these cars share is that their discs are made of carbon. The differences in the brake discs are outlined in the table below:
The difference in the disc diameter is linked to the size of the rims used in the respective championship races. Currently in Formula 1, 13″ rims are allowed. At the 24 Hours of Le Mans the cars are equipped with 18″ rims.
TWO EXTREMES IN VENTILATION
In Formula 1, ventilation is crucial to preventing the system from overheating. Depending on the forecasted air temperatures during a Grand Prix and the specific race strategy, each driver chooses from three different Brembo disc solutions: Around 900, 1,200 or 1,400 holes.
The teams rely on personalized cooling schemes, an element that is essential for improving heat dissipation. The temperature of the F1 discs can get up as high as 1,832°F during the race. Ventilation of the LMP1 cars is not as intense at the 24 Hours of Le Mans because the teams actually have the opposite problem: Rather than cool down the systems, they have to keep the temperature from dropping too low, especially at night or during Safety Car / extended Yellow phases.
That explains why these cars use the same number of ventilation holes that the Formula 1 cars used years ago. At Le Mans, it is important to keep the carbon discs from dropping below 662°F, which would cause the friction material to glaze, reducing braking efficiency and resulting in premature disc wear.
To prevent this from happening, Brembo offers friction material for discs and pads that has a more efficient thermal conductivity.
DIFFERENT WEAR, INTEGRATED CHECKS
Just like in Formula 1, the LMP1 cars racing in the 24 Hours of Le Mans use Brembo carbon brake pads. Naturally, the pads they use are thicker to guarantee they remain fully operational for the entire 24 hours.
Just consider that pad and disc wear during a Formula 1 race is less than one millimeter, while the prototypes racing in Le Mans consume 3-4 mm per disc and 8-10 mm per pad.
To monitor consumption, the Formula 1 single-seaters are equipped with sensors that continuously relay the temperature of the discs and calipers to the engineers in the pits. In some cases, the sensors also monitor the status of the pistons so that they can calculate disc and pad wear.
Monitoring these elements enables proactive problem-solving in different conditions of use and communication with the driver in real time about modifying brake balance and recovering energy from braking.
In addition to sensors, the Brembo discs on the prototypes at Le Mans have slots with a range of depths that make it easy to quickly check the status of the discs when the car is in the pits for refueling or to change the driver. When one of these slots is no longer visible, it means the disc has been consumed more than the depth of the slot when new.
Obviously, when the last slot disappears, the disc has to be replaced because the level of performance has gone down.
BRAKING PERFORMANCE COMPARISON
It may seem impossible to compare the braking performance of these two types of cars since they don’t race on the same track.
To get around this problem, we decided to compare the hardest braking done in the two competitions, calculating the average deceleration of each as it relates to braking time and distance. In general, the Formula 1 and LMP1 cars are very different and their behavior during braking can’t and shouldn’t be attributed to the brakes alone.
The race cars have different weight distributions and aerodynamic loads, but even more importantly their tires differ in size and compound, which plays a significant role in braking performance. Although not perfect, this comparison still provided interesting results.
LMP1: LONGEST BRAKING ABOUT 65 FEET PER SECOND
On Chicane 1 at Le Mans (turn 5 on the track), the LMP1s arrive going 208 mph and they brake for 3.21 seconds during which they travel 195 metres.
This is how they drop to 68 mph, the fastest possible speed to get through the chicane without driving off the track. To do this, drivers apply a load of 100kg on the brake pedal and undergo a deceleration of 3.5 G.
In comparison, as the Formula 1 cars enter the Parabolica at Monza (the last turn on the Italian GP track), they are going 195 mph and in just 1.22 seconds they use barely 72 metres to reduce their speed to 127 mph.
The drivers are required to apply a remarkable amount of force: 6.7 G in deceleration and a load of just over 200kg on the brake pedal.
That means a Formula 1 race car is able to drop more than 55 mph [195-127 mph)/1.22] in one second, while the top-end LMP1 cars can only reduce their speeds by 43 mph [(208-68 mph)/3.21] per second.
On Turn 1 of the Marina Bay Street Circuit in Singapore, the Formula 1 single-seaters brake for 1.98 seconds to go from 183 mph to 84 mph: That means in one second they drop more than 50 mph. And on the first corner after the tunnel (Turn 10) at the Monaco GP, the single-seaters go from 178 mph to 58 mph in 2.03 seconds: In essence, in one second they decelerate 59 mph.
The difference may seem minimal, but said another way it really is impressive: In 72 metres of braking, the Formula 1 single-seaters go down more than 65 mph, while in the same amount of space the LMP1 prototypes decrease their speeds by about 43 mph.
On Chicane 1 at Circuit de la Sarthe, every metre of braking corresponds to a drop of 0.7 mph in speed, while on the Variante del Rettifilo, every metre of braking leads to a reduction of 1.05 mph in speed.
In summary, in a hypothetical braking competition between F1 single-seaters and LMP1 race cars, during the first 300 miles on the track, the Formula 1 cars outshine by a long shot. But, we should not forget that the Formula 1 car would have exhausted it brakes by the fourth hour of the 24 Hours of Le Mans and be in for extensive servicing. An LMP1 car has barely warmed up!