Anyone can build complicated. Our actions are determined by simplicity.
- Sergei Korolev, Chief Designer of Sputnik, Vostok, and Soyuz.
Keep it simple stupid!
- Kelly Johnson, Chief Engineer at the Lockheed Skunk Works.
Trucks are heavy. This is a simple statement of fact. They have always been heavy for their entire history, and while there have been some modest steps towards weight-saving, they are largely token steps which don’t really address the core of the weight problem.
But why is this a problem? We all have a mental model of a truck, and that mental model is everything is beefy and heavy — it obviously needs to be tough to handle the rigours of truck life. But is this actually true? The problem with heavy trucks is that, to put it simply, to move additional mass over a given distance at a given speed requires substantial additional energy. This energy must be stored somewhere, and then it takes further energy to move the additional mass, and so on, in a vicious cycle¹. This results in significant built-in inefficiencies in the logistics sector — not just the environmental and emissions, but also economically. When we pay for a truck to be on the road, to be delivering goods, most of what the energy cost we’re paying for actually goes to propel things which aren’t the final product, i.e., the actual goods — instead most of it is being used to move, well, bits of truck.
Thinking about it, this is actually a major issue as we are paying for this as a society — we pay for it economically, with our wallets, to move around a bunch of dumb weight that isn’t actually useful, we pay for the cost models of trucks associated with their bills of materials and the capital expenditures to manufacture them, with the wear and tear on our roads to bear the weight of the heavy trucks, and we pay for it ecologically, with the additional emissions to move the weight around, with the additional emissions to manufacture all that stuff in the first place and to deliver it to the factory², and with additional tyre and brake consumption, and so on, all these things that come along with the weight. And we, as society, have decided that this situation is acceptable, and have done so for decades!
In the context of anthropogenic climate change, and in the context of rising energy costs (and cost of living), this is no longer acceptable.
So what is the answer?
Famed automobile engineer and founder of Lotus Cars Colin Chapman understood precisely this problem in the 1960s — his famous axiom about building cars, was to
Simplify, and add lightness.
While the essence is simple — use the least amount of parts to achieve the best performance — there is a world of depth in these four words; let us unpick them.
Simplify: If a part is not there, it doesn’t take up: mass, volume, cost, materials, energy, overhead³.
Add lightness: Optimise for best performance, to make it as light as possible while meeting the safety, technical, and commercial (price) requirements. Generally a component using fewer materials will cost less than a component using more materials.
This approach led to Chapman’s groundbreaking racecars (and to the founding of Lotus Cars as a way of financing those racecars). But contemporary with Chapman, this same logic is the underlying principle and philosophy that was adopted wholesale in the aerospace industry, whether that was commercial aircraft, military warplanes, or rocketry, and is now applied widely within the passenger automotive industry and even to the passenger rail industry. So why hasn’t the truck industry adapted to this axiom?
A diesel truck is largely insensitive to the requirement to store more energy, because of the enormous latent energy carried in diesel fuel, the inefficiency of accessing that energy (i.e., most of the energy carried in fuels such as diesel is wasted⁴), and the simple way to add more energy (add a larger fuel tank).
However, an electric vehicle is hugely sensitive to energy efficiency, because batteries don’t store as much energy as liquid hydrocarbons like diesel or gasoline do — the best lithium batteries in the world today still only store about 1/10 the energy per unit mass compared to the enormous amount of energy found in the bonds of liquid hydrocarbons.
How to solve this problem of improving systemic energy efficiency in an electric vehicle, without going to complex and complicated Rube Goldbergian style solutions? The simplest solution is to save weight by eliminating unnecessary material through sophisticated and smart design⁵.
This is a difficult thing to do, but it is possible, and it allows for a whole lot of advantages.
There are a number of factors that result in heavy trucks, but fundamentally, the existing paradigm dictates the requirements for a comparatively heavy powertrain and chassis (with respect to usable payload weight).
Conventional powertrains, whether diesel or electric — as described in one of my earlier pieces — transmit the power mechanically, like a Victorian mill, using shafts and linkages⁶ — these have to be very heavy to transmit the high levels of power necessary to propel the weight of the truck + the weight of the payload. This power is rotational — that is to say, torque — and so there is an awful lot of rotating mass, with the goal being to eventually turn the road wheels at some point.
This imparts significant twisting forces — torsional loads — to the chassis, resulting in a beefed-up chassis to counteract these massive forces (the chassis needs to be strong enough to withstand these forces without twisting itself up).
With a heavy chassis and heavy powertrain as the foundation, there is no way for a conventional truck design to be adapted to be lighter weight, beyond very marginal gains. Since the chassis is undergoing this flex all the time, it dictates the need for a separate cab and a separate payload box, which themselves need to be self-supporting structures which are built on top of other structures and so on. Finally all of these components need to be fastened together, usually using nuts and bolts, and so there is the weight of the fasteners, the cost associated with manufacturing, purchasing, and storing those fasteners, and then the labour associated with installing these (and all those failure points that are introduced!). All of these inherent inefficiencies are, as I wrote earlier, paid for by society.
The most pertinent observation here is that neither cars, nor planes, nor passenger trains are bolted together anymore — this was one of the first things that the aerospace industry did away with, all with a view to weight-saving to improve performance.
At Bristol Superlight, we brought an aerospace type design philosophy to the commercial vehicle industry. This is apparent not just in our approach to vehicle controls, but also our physical architecture, including the materials we use, and the technologies and techniques we use for joining those materials together.
The very first thing we did was simplify — we eliminated the entire mechanical powertrain. We replaced it with electronics, which do not weigh much, and with software, which weighs nothing. We did this to liberate huge amounts of efficiency, since we no longer had to deal with mechanical transmission losses. This further allowed us to eliminate a whole bunch of material that was no longer necessary to counteract the twisting forces that are inherent to a mechanical powertrain layout.
The advantage of not installing the material in the first place, is that the material does not need to be:
- Manufactured, with the economic and ecological cost of manufacture
- Purchased, alleviating time and administrative expense
- Transported to its place of installation
- Handled and stored
- Installed
- Carried around for the service life of the vehicle, with the attendant energy, economic, and maintenance and repair costs
- And if it is not there — it cannot go wrong or fail!
The next step was to add lightness. This entailed using the material we would carry as intelligently as possible — and ideally to use that material for more than one purpose, at the same time. This is most evident in the structures we can design. Lightweight structures can carry significant payloads and can withstand enormous forces (such as in a crash). Cars, aircraft, and even commuter trains have undergone a transition to lightweight multipurpose structures known as monocoques.
Monocoques are self-integral structures which fulfil multiple functions — in road going vehicles they carry the weight of the payload (and overload conditions), but they also withstand potholes and kerb strikes, they are designed to protect drivers and occupants and pedestrians through what are known as “crash structures”, and so on. The use of multipurpose structures — as opposed to single-function structures (which, as the name suggests, perform a single function i.e., “carry the payload” “compartment for the driver” etc) drives down weight, and improves system efficiency (and in the case of a truck, increase the available payload capacity to improve the ratio between “truck” and “payload”), but the use of fewer materials also drives down the cost-per-vehicle as well as the capital cost required to manufacture the vehicle. There is a reason the entire passenger automotive industry has transitioned in the last few years to multipurpose monocoque structures!
It is clear that lightweighting is a virtuous circle, with many advantages. Yet why is everything on a truck so darn heavy? It does not need to be this way — and we’ve proved it.
¹As I mentioned in Lost in Transmission, Tsiolkovsky’s Rocket Equation (or Tyranny of the Rocket Equation) dictates that the more fuel you have, the more fuel you need (i.e., fuel needs to be added to propel the fuel that is added to propel…) ^
² On more heavy trucks! ^
³ Elon Musk (in the context of SpaceX rocketry) recently restated this as, “the best part is no part”. ^
⁴ Upwards of 80% of the energy stored in liquid fuel such as diesel is wasted in a commercial vehicle on, to misquote Shakespeare, “sound and fury” — i.e., as heat (engine gets hot) and sound (engine is noisy). ^
⁵ As Korolev implies, complexity is not the same as sophistication. ^
⁶ Amusingly enough, the entire way trucks have been built for the last century is the very antithesis of Korolev’s or Kelly’s observations — liquid fuel is squirted into chambers which, under compression, self-ignites, with the force of the explosion causing a very complicated sequence of parts to convert reciprocating motion into rotational motion, and then transmit that through a series of gears, shafts, and linkages, to the point where it is then perpendicularly delivered to the road with a complex invention (the differential) created by Leonardo da Vinci in the late 1400s. Phew! ^