Electric vs. Petrol Race cars - Which is better?
While many people (myself included) prefer the visceral experience of the internal combustion engine, the automotive industry is slowly moving towards the electric car as the way of the future. The benefits in road cars are obvious, the efficiency is much higher, you can package the car with a lot more boot space, and you can charge the car cheaply from the comfort of your own home. But what are the pros and cons for performance in race cars?
To start off with, lets talk about the performance advantages the ICE has, because they are actually pretty limited in scope. The biggest advantage held is that of weight, and this is a big one for racing. The energy density of gasoline is 12,000 wh/kg, whereas even the best car batteries are only around 200 wh/kg. Consequently, for the conceivable future electric vehicles are going to be heavier than petrol vehicles for a given range. This is despite the improved energy efficiency of electric vehicles, from both more efficient drivetrains and energy recovery through regenerative braking.
Most people know weight is bad for racecars, but why? If you have sufficient power, it won't slow you down in a straight line , what it will do though, is cause two run on effects. One, tyres do not maintain a constant grip coefficient with constant vertical load. As you add weight, the grip coefficient decreases, so your tyres are working less efficiently.
The other big issue with weight for racecars is downforce performance. You need the same downforce/weight ratio to achieve the same sort of cornering forces. This means as the weight of the car increases, you need to add downforce, which may be a problem as you may already be extracting as much from the air as you can. As such, heavier cars are always going to struggle in high end or downforce dominated racing as their cornering grip is comparatively low.
However, if the weight of electric cars ever gets into a similar place as internal combustion cars, then they are going to dominate. Electric cars are more efficient, which means less heat produced for a given power level, which means less cooling. Currently Formula E has a few cooling issues with the rotors in the motor and the battery pack, but this will eventually be effectively overcome. This allows us to package a car tighter, and reduce the size of cooling openings and exits and improving overall aero. Electric motors are compact, and cells can be distributed around the car, so this will further enhance our packaging.
Battery cells come with pros and cons, they are tricky to cool, but can be distributed around the car for better mass distribution and packaging.
Electric motors have a lot of mechanical benefits too. Just this year we saw Honda struggling with drivetrain (both engine and gearbox vibration related) issues in F1 , and this is something that is far less of an issue with electric motors as they deliver smooth torque with no reciprocating parts. This torque is also typically delivered in a manner that gives a wider power band than a combustion engine. You can get rid of the clutch, removing reliability issues associated with it. The motors have very precise control of wheel speed and torque, and when you combine this with a motor powering each wheel you end up with very precise traction control, stability control and torque vectoring. You can use this in transient scenarios such as corner entry and exit to help with the yaw acceleration.
So basically, electric cars will be vastly superior to combustion powered cars on track in the future, but due to the current massive weight penalty, you can sleep easy as combustion is superior for now. For more information and details check out the video!
Kyle Forster is a qualified Aerodynamicist, race car engineer, and the man behind JKF Aero, a firm that offers a variety of aerodynamic consultancy services for racing purposes. If you have any questions for Kyle or have any suggestions for future videos, drop them in the comments below!