Formula E Gen4 with a "virtual prop shaft": How software becomes a key performance factor

Part of the mechanics is moving into software with Formula E's Gen4 cars: The front and rear axles operate independently, with their connection handled by a "virtual prop shaft". For Stellantis, that opens up major new possibilities in vehicle dynamics and performance. Simulation engineer Teena Gade explains why software is becoming a key part of the new Formula E car - and why the extreme standing starts are already making her think about the physical limits of the drivers.

With 600 kW available in qualifying and permanent all-wheel drive, the Gen4 cars represent a major step in performance. The Gen3 Evo also uses all-wheel drive in qualifying, but the maximum power available at the front axle increases by 250 kW with Gen4. That is a significant difference for the drivers as well as the engineers.

In the first two parts of our Gen4 series, Gade explained why Stellantis runs up to 10,000 simulations per month for a single component and why key hardware decisions had to be made as early as 18 months before the first race. In part three, the focus shifts to software: In Gen4, it even replaces the mechanical connection between the front and rear axles.

"You still have a front motor and a rear motor, and they're fully independent," Gade explains to e-Formula.news during Citroen Racing's Gen4 testing in Guadix. "There's no mechanical connection between the two drivetrains. In an old-school rally car, you would have had a prop shaft between them. The prop shaft is now virtual; that now lives in the software. That's the very, very big difference."

Software instead of a prop shaft: Gen4 gives manufacturers new freedom

Especially when it comes to vehicle set-up, the Gen4 regulations give manufacturers entirely new possibilities.

"We have active differentials, which means the level of control we have over how the car handles is massive. We also have full software freedom, so we are free to do whatever we want in terms of ABS, traction control and lateral handling dynamics." Software therefore becomes one of the key performance factors in Gen4.

"There are a lot of similarities when it comes to simulation in Formula 1," says Gade. There is one crucial difference, however: "In Formula 1, it's all about aerodynamics. You change the aero map and then use the simulator to see how that changes the way the car drives. In Formula E, what we're saying is: If we change the software like this, how does that change the way the car drives - and how does it change the racing?"

"From an engineering perspective, that's extremely exciting. But from a driver's perspective, I believe it's extremely exciting as well because the car is a real performance car. We're pushing the limits of electric technology."

According to Gade, the reactions from drivers who have already tested the car reflect that step: "Every driver that gets out of this car for the first time says: Wow, that is something else. That really is something."

But with performance continuing to increase, Gade says an unusual question is beginning to emerge: How much acceleration can the human body actually take?

"The standing starts are insane now. They are completely crazy, and I'm sure physically that's actually quite hard for the drivers because everything is happening so fast and you can feel the car moving underneath you," she says. "I honestly don't know what the human limit is for how much faster we can go in a standing start."

When will a Formula E driver need a G-suit?

The Gen3 Evo already accelerates from 0 to 100 km/h in around 1.8 seconds. With Gen4, the available power rises significantly again. Gade therefore draws an unusual comparison with aviation.

"If you look at fast jet aircraft, they're pulling something like 8 g in a turn, and if it wasn't for the G-suit, the pilots would be blacking out," she says. "If you'd asked me 15 years ago whether a road car would ever get to those levels, I would probably have said no, because there weren't tyres that could sustain it."

Gade takes the idea one deliberately provocative step further: "At what point are we going to need G-suits? I don't know. We can't be far away."