Every automaker is desperate nowadays to find new ways of gaining fuel efficiency, especially now that electric cars are beginning to carve out a corner of the market. Some new cars, like the Tesla Model 3, come with cool space-age looking aerodynamic wheel covers to be more efficient—but why doesn’t every new car do the same?
Of course, the fuel or energy efficiency of a vehicle isn’t only based on aerodynamics, but since it’s what impacts a lot of the exterior design of the car, it’s what many people associate with efficiency.
Take the new Tesla Model 3, for example. It comes with optional 18-inch wheel covers that, according to Tesla’s Vice President of Engineering, increases the car’s efficiency by as much as 10 percent. But this is only an option for those willing to sacrifice the style of the other 18-inch and 19-inch options.
InsideEVs looked into why more cars, especially internal combustion engine (ICE) cars desperate for gains in efficiency, don’t adopt the same aerodynamic wheel covers.
The Ford Focus EV did not come with aerodynamic wheel covers, but it’s useful as an example to gather information about overall vehicle efficiency, because it was once available as both an electric car and an ICE car with the same basic body style. This makes it easier to draw comparisons between the two powertrains, and we can then make some conclusions about how wheels could effect each version’s overall efficiency.
The article proposed comparing the Focus ICE and Focus EV in a scenario where both travel 60 miles at highway speeds. Over this span, the ICE consumes 60 kWh of energy from fuel at approximately 34 MPG, the EPA rating for this Ford Focus model, compared to the Focus EV’s consumption of 21 kWh. So the gas-powered car requires more energy to go the same distance at the same speeds compared to the electric car.
It goes on to break down why that’s the case:
The Focus ICE and EV versions are almost identical, so you would not expect the aerodynamic or rolling resistance losses to be significantly different. The dramatic change is for the powertrain losses, which have dropped from 45 kWh ICE to 6 kWh for the EV.
The following chart breaks down where the energy is consumed in this example for the ICE and EV, while keeping the wind, rolling, fans, and light losses the same between the EV and ICE. Again, we’re assuming highway speeds for one hour. These are probably not 100% precise for the Ford Focus but are based on typical averages which are directionally correct for this example.
And the conclusion InsideEVs came to:
For the ICE, 75% of the losses are in the engine/drivetrain. If you can engineer a 10% improvement in the engine/drivetrain, the vehicle will get 7.5% (75% of total losses x 10% improvement) more efficient. The reality is getting a 10% efficiency gain in the powertrain of an ICE vehicle is difficult. This also explains why there is a large amount of cost and complexity in today’s ICE vehicles with turbos, variable timing, etc.
Additionally, a 10% improvement in the aerodynamics of an ICE vehicle gets very little efficiency improvement on the highway. It’s 15% of the total losses and a 10% improvement would only yield a 1.5% improvement in vehicle efficiency. This explains why few ICE vehicles rely on aero type wheel covers.
For the Focus, adding wheel covers to the ICE would have even less gains in overall efficiency, because the aerodynamics of the car aren’t really the problem.
Even for the Model 3, it would seem that the wheel cover’s claimed 10 percent gain in efficiency actually only translates to a 10 percent gain in aerodynamic efficiency, meaning they’re actually only about four percent more efficient than a standard wheel overall.
So there you have it. If you were about to go rushing out to snap on some snazzy saucers to your gas-powered ride, or even your electric car, it may not even be worth it! Personally, if I’m rolling around in a fancy new EV, I want it to look the part. I dig the wheels and would rock them anyway.
Check out the full article on InsideEVs for more insights on ICE versus EV efficiency.