Critical mass
The automotive industry is suffering from ‘autobesity’. How did this emerge, and what can be done about it?
Motorsport has always been a crucible for innovation; an arena where efficiency, performance and regulation collide under extreme conditions. Yet a quieter, more insidious trend has been unfolding both on the track and on the road: autobesity. Put simply, cars are becoming heavier.
What might once have been dismissed as a by-product of safety improvements, or technological progress, has become a central engineering challenge, one with profound implications for performance, sustainability and the future of racing and motoring.
The growth in vehicle mass is not a uniquely motorsport phenomenon. Road cars have steadily gained weight, due to a combination of factors: enhanced crash structures; larger dimensions; hybrid and fully electric powertrains; and consumer preference for SUVs (so-called Sport Utility Vehicles). These same drivers, especially safety and electrification, have translated directly into numerous racing categories.
Unforgiving physics
Formula 1 offers a clear illustration: since the introduction of hybrid power units in 2014, minimum car weight has risen dramatically.
The addition of energy recovery systems and increasingly robust safety structures, such as the Halo, has pushed cars well beyond their historical norms. In addition, larger cars provide better aerodynamic platforms – albeit at the cost of more challenging overtakes. Similar trends can be observed in endurance racing, Formula E, and even some junior categories.
Of course, this weight gain is not without consequence. Engineers instinctively understand that mass is the enemy of performance. It increases inertia, reduces responsiveness and places greater demands on tyres, brakes and energy systems. But the implications extend far beyond lap time.
At its most fundamental level, the relationship between mass and energy is unavoidable. Moving a heavier object requires more work, more work requires more energy, and more energy, whether derived from a liquid fuel or electricity, implies greater environmental impact. This is not merely a theoretical construct. Even in highly optimised systems, the laws of physics impose limits that no amount of engineering ingenuity can fully overcome. In motorsport, this manifests in multiple ways:
What might once have been dismissed as a by-product of safety improvements, or technological progress, has become a central engineering challenge
• Fuel or energy usage increases with mass, a ecting stint length and strategy.
• Tyre degradation accelerates under higher loads.
• Braking systems must dissipate more kinetic energy, increasing wear and temperatures.
• Cornering performance su ers due to higher lateral loads and inertia.
These are not independent e ects, they compound one another. A heavier car requires stronger components, which also add weight, a feedback loop engineers are constantly battling.
Beyond conjecture
As I expand on in my recent book, Critical Mass, co-authored with Nicholas Molden, energy consumption is intrinsically linked to mass, but so is much else. We argue that the environmental impact of a vehicle can be best approximated by the product (multiple) of vehicle mass and distance travelled. We call this the Molden-Leach Conjecture.
It’s a bold claim, but one that is grounded in extensive analysis. Vehicle mass correlates strongly with the following:
• Energy consumption, and hence CO emissions
• Lifecycle emissions
• Non-exhaust emissions (for example, tyre and brake wear)
• Infrastructure impact
• Noise
• Safety externalities
Indeed, 83 per cent of regulated pollutants that remain problematic are strongly linked to car weight.
Electri cation has been heralded as a solution to environmental concerns, both in road transport and motorsport. Yet it introduces a paradox: while electric powertrains can be highly e cient, they are also inherently heavy. Battery systems, even with ongoing improvements in energy density, remain signi cantly heavier than equivalent energy storage approaches.
In Formula E, for example, the battery pack represents around 37 per cent of total vehicle mass in Gen3. In F1 and endurance racing, hybrid systems add signi cant complexity and weight, even as they improve e ciency.
The bene ts of electri cation are immense, but we must not be blind to the costs. In recent years, we have spent a lot of time thinking about choosing technological solutions, rather than thinking more holistically. For motorsport and automotive engineers, this raises a critical question: are we optimising the right variable?
Hidden costs
The e ect of vehicle mass on its environmental impact extends far beyond tailpipe emissions. This is especially relevant in motorsport, where the focus is often on fuel e ciency or energy recovery.
Non-exhaust emissions, such as tyre wear, brake dust, and road surface degradation are increasingly recognised as signi cant contributors to global air pollution. These e ects scale directly with vehicle mass.
We argue that the environmental impact of a vehicle can be best approximated by the product (multiple) of vehicle mass and distance travelled. We call this the MoldenLeach Conjecture
Heavier cars generate more particulate matter, regardless of powertrain. This is particularly true in a world where internal combustion engine vehicles have lters at the tailpipe, near eliminating this as a source of these emissions.
Similarly, noise and safety impacts are strongly in uenced by mass. Larger, heavier vehicles carry more kinetic energy, increasing the severity of collisions. While crash structures in the vehicle increase protection for the occupants, the impact on things the vehicle hits increases substantially with mass. Indeed, this is a classic ‘externality’ problem: something that may bene t the individual (eg increased safety or performance) but imposes costs on society.
Where does it end? Is the safest vehicle for me and my family a tank?
The impacts on our infrastructure are perhaps the most noticeable, but least connected to vehicle weight. Increasing potholes, closed bridges and essential upgrades to
If we can align lighter racecars with lighter road cars, then ‘race on Sunday, sell on Monday’ will have a new impetus, and open a new avenue in consumer innovation and amenity
multi-storey car parks are all in part due to the increases in vehicle weight we see everywhere. Not just with EVs.
Finding it harder to fit in a parking space? Unsurprising, because the cars we drive have become bigger. Without our roads and car parks growing, there is simply less space for them. This is perhaps best illustrated by the fact that in the UK, the ‘standard’ highway width is 7.5m. This was easily enough for two parked cars and two passing cars 100 years ago. Today, it’s barely enough for a single passing car with two parked cars.
This is analogous to the larger motorsport cars today having better aerodynamic platforms, but being much harder to pass.
The vast majority of racetracks have not been made wider!
Complexity vs simplicity
Modern motorsport regulations are complex, reflecting the multifaceted nature of performance and sustainability. Fuel flow limits, energy recovery caps, Balance of Performance (BoP), and cost caps all attempt to balance competition with efficiency. One approach would be to bring in increased incentives to optimise for mass alongside these (though the lap time penalty for being overweight is already pretty severe).
But what if, instead of increasing complexity further, we simplified? Is there a world where simpler regulatory approaches, focusing more on mass, could be more effective? They might have the side benefit of being easier to understand as well!
Such approaches would not eliminate the need for other regulations, but could provide a clearer direction for engineering development in the future.
On the road regulation can help too, and now is the time. Petrol tax is beginning to run out of steam as electrification of road cars becomes a reality. Love it or hate it, governments around the world are not going to want to give up such a lucrative source of revenue.
So, a taxation based on the product of vehicle mass and annual distance travelled (which could be picked up at the car’s annual service) is an attractive alternative to things like road pricing, which brings substantial privacy concerns, or taxing electricity for vehicles, which has practical challenges. This could be done in a revenue neutral way and phased in as the proportion of electric vehicles increases.
Leadership opportunity
Historically, motorsport has led the way in automotive innovation; from aerodynamics to hybridisation. The current moment presents another opportunity for leadership. Motorsport plays an immense role in shaping broader trends, and the number of eyeballs it attracts each week is outstanding. By prioritising lightweight design and efficiency, racing can set an example for the wider industry.
The FIA’s ‘nimble car’ concept, which is at the heart of 2026 F1 technical regulations, is a step in the right direction. Let’s now follow this path in other series, as well as in the next iteration of grand prix cars.
This is not without precedent.
The fuel crises of the 1970s drove significant reductions in vehicle weight and improvements in efficiency. Motorsport responded with innovations that eventually filtered down to road cars. Today’s challenge is different, but no less urgent. Energy markets, climate change, resource constraints, safety, infrastructure and regulatory pressures are rapidly reshaping the automotive landscape. Motorsport must decide if it follows or leads.
It would be naïve to suggest that reducing mass is straightforward. Many of the factors driving weight increase, particularly occupant safety, are non-negotiable. Crash structures, driver protection systems and robust components are essential. Similarly, hybrid systems and electrification bring performance and efficiency benefits that cannot be ignored. Or certainly are not being ignored.
The challenge, therefore, is to innovate while preserving these benefits. Areas where such innovation could occur include: lightweight materials (composites, alloys); advanced manufacturing processes (AM, for example); aerodynamics (including active aero) to enable smaller platforms; battery innovations; and, ultimately, integrated systems thinking. In addition, the ‘soft power’ of motorsport should be brought to bear, reversing current fashions that indicate bigger is better.
The best news of all is that this can all be done. The McMurtry Spéirling is leading the way. This small, battery electric vehicle, weighing only 900kg, holds both the Goodwood Festival of Speed hillclimb record and the Top
Gear test track record. It’s a very impressive piece of engineering.
Reframing the problem
For decades, motorsport engineering has been defined by the pursuit of marginal gains; finding minute performance improvements in ever more complex systems. We have lost sight of mass in the regulations and in society, yet it is a dominant factor in both performance and environmental impact.
Consequently, it demands a central place in engineering decision making. We must refocus our innovation, and motorsport should lead the way. If we can align lighter racecars with lighter road cars, then ‘race on Sunday, sell on Monday’ will have a new impetus, and open a new avenue in consumer innovation and amenity.
Motorsport has always thrived on clear objectives: go faster, last longer, win. Now it is time to add another: weigh less. We need to put all of our cars on a diet.
Dr Felix Leach is an associate professor of engineering science at University of Oxford. With Nick Molden he co-authored the book Critical Mass: The One Thing You Need to Know About Green Cars, published in 2024.
What if, instead of increasing complexity further, we simplified? Is there a world where simpler regulatory approaches, focusing more on mass, could be more effective?