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14/05/2019
Electric racers in rome's grand prix

Formula E

 

Renewed partnership with Michelin to race on tires designed for the new generation of Formula E racers

Nicodemo Angì

The FIA Formula E championship is now a new point of reference in motorsports. Let us take a closer look at how Michelin designs and prepares the "shoes" of these exciting electric single-seaters. The Italian stage of the FIA Formula E championship, which takes place in the beautiful surroundings of the city of Rome, has just taken place, with record-breaking attendance figures. You might recall our report on last year’s Rome Grand Prix published in the third issue of Pneurama in 2018.

That Grand Prix was to some extent historic, given that it was the first to take place in the capital since 1951: the environmental sustainability of the Formula E Championship and almost non-existent noise pollution, guaranteed a much appreciated return in the Capital much to the delight of the many enthusiasts. The first GP in Rome was also the last one raced with First Generation racers: this year’s championship, in fact, saw the debut of Gen 2 “Bat-mobile-like” single-seaters with wings and fairings just about everywhere on the car. 

 

Electric Bat-mobile

The technical differences are clearly visible, starting from larger battery packs able to go the full distance while delivering more power at the same time. What has not changed, is the commitment Michelin has lavished on Formula E racers enabling them to perform at best in all conditions. Let us now take a closer look at some of the differences between this year’s Gen 2 single-seaters and last year’s Gen 1. The overall length is 16 cm longer and has is now 5.16 m, while the width is 1.77m, one cm less than last year. The overall height and ground clearance remained unchanged and still stand at 1.05 m and 7.5 cm respectively, much like the wheelbase which remains 3.1 metres. On the other hand, both axle tracks have increased: by 2.5 cm at the front reaching 1.553 m, and by 13mm at the rear now 1.505 m. The maximum power produced by the batteries rose to 250 kW, which means an increase of 50 kW, and translates into 339.9 hp; the actual power output of the motors will anyway be slightly lower.

 

More KW, more braking power

As in the previous season, power is limited during the race: the 200 kW allowed this season are equivalent to 272 hp, which means an increase of 20 kW/27 hp compared to the 2017/2018 championship. On the other hand, great attention was paid to the regenerative braking system which rose by 100 kW and now stands at 250 kW enabling the system to supply greater Energy to the larger batteries. While it is easy to think that the nominal capacity of the batteries would at least be double compared to the 28 kWh provided by Gen 1 batteries, we now know precisely that Gen 2 batteries can deliver a maximum of 52 kWh during a race. The minimum weight allowed (including the driver) has also gone up by 20 kg, and it is now 900 kg. Not exactly a feather, but the readiness of the electric motor still allows them to accelerate from 0 to 100 km/h in just 2.8 seconds, a time comparable to that of a Formula 1.

Torque vectoring, stability and traction control are still prohibited; differentials with hydraulic or electronically controlled torque distribution are also banned, but a viscous coupler is allowed provided it is not equivalent to a controlled self-locking device. Sending telemetric data to the pits it is still not allowed, but the driver can communicate by radio with the team. A series of sensors are entrusted with collecting different data that are then stored in a data-logger regulated by the FIA. Among the several parameters collected we find voltage and current output from the battery, torque and engine speed, the pressure of the brake circuits and the temperature of the battery. The rules relating the electric motors have also been changed since last year: the maximum allowed is 2, always connected to each other, and the minimum thickness of the laminations that convey the magnetic flux of the coils remains, no thinner than 5 hundredths of a millimetre in an attempt to limit costs.

 

Digital “brain”

The suspensions are also regulated: in order to keep costs down composite materials are not allowed, and their design is fixed at the front and free at the rear as power-trains can have different dimensions. The biggest news, though, relates to the braking system, now brake-by-wire, to make braking more predictable. Gen 1 cars had a regenerative braking system that was adjustable by the driver but the combination of the two types (energy recovery and friction) generated irregular braking forces at the rear. Gen 2 single-seaters use an ECU that detects just how much pressure was applied by the driver and balances the regenerative action with the conventional braking. Teams are free to decide on the material of the discs while the callipers must be made of light alloy; the system is supplied by Brembo.

Now to the wheels: no composite materials here either and non-modular, they must have a 9" width at the front and 11" at the rear with a diameter of 18 inches. Bear in mind that this measure was strongly desired by Michelin as it is also used by road cars and therefore allows a quick transfer of know-how gained in racing. The specially designed Michelin Pilot Sport tires are 235/40 at the front (last year they were 245/40) and 305/40 for the rear axle.

 

Tires, a relentless evolution

The result of a long and painstaking research, the tires have been constantly improved and they now represent the third generation of Michelin’s Pilot Sport. It is the lightest available today. This improves not only performance but also the environmental impact as this reduces the amount of raw materials transported and used in production and then recycled.

Thanks to the work of the Motorsport department, the new Michelin Pilot Sport is 2 kg lighter on each of the front tires and almost 2.5 kg for the rear tires compared to the previous model. This is equivalent to about 9 kg per each set, almost 20% less: this, combined with the aforementioned regulation that has increased the minimum weight by 20 kg, gave designers a little leeway to work on advanced technologies.

Michelin points out that tires account for about 20-25% of the energy consumed by road vehicles and this is even more critical when it comes to electric vehicles. Older Pilot Sports had already lowered this share by 16%, giving Formula E racers 2 km more (about half a lap of a circuit) mileage: the third generation of Pilot Sport are expected to follow the same pattern.

The 18-inch diameter and the tread (bear in mind that these single tires are also used in wet conditions) make Michelin’s Pilot Sport rather similar to normal road tires. Obviously the technologies used in the tread are more than confidential and protected but their similarity to road tires facilitates, no doubt, a quick transfer of data collected during the E-Prix. The efforts made by Michelin for its new Pilot Sports appear even more remarkable when we consider that these improvements were made on a tire that will go the whole distance (its predecessor was used only for about half of a race) while retaining the same safety and handling characteristics of the previous generation.

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