In this article I will discuss the concepts and work being done around lightweight designs. The article follows on from a recent description of the ladder chassis. The downside of the ladder chassis is that the body sits on top and the whole vehicle can be quite heavy. Conceptually, this is a simple topic, but in practice is somewhat more difficult to achieve.
It is simple because the lighter the weight of a vehicle, the two choices you have: 1 – slot in a small engine and you have a very fuel efficient car for longer times between refuelling or 2, shove in a high powered engine and you have a super quick vehicle. Choice 2 was the path that Carroll Shelby and Jack Griffiths took with the AC Cobra and TVR Griffiths respectively. These cars influenced the Sunbeam Tiger and several others during the 1960s to get a bigger bang for the buck.
In practice as a designer, you have to weigh up the issue of strength over lightness. Audi, for example, have a team looking at each of the components in their cars and redesigning them as lighter but stronger units. They have saved several kilos in each car’s weight by doing this. Each kilo saved helps to improve the efficiency of the car by reducing the amount of ballast that the engine has to pull along.
A few years ago, Lotus bought an offshoot of Holden based in the UK and then renamed it Lotus Lightweight Structures. The company manufactures aluminium and composite structures including the lightweight chassis for the Lotus range of cars. The company has a wide range of customers that they supply specialist equipment to.
This is where the space frame chassis comes in. By using this concept and built with lightweight alloys means that the core structure is super light and very strong. There is no argument as to why race cars use this type of chassis with a composite tub.
The biggest part of the car is its body and this is where many designers start. Like many ideas, it is not a new idea to try and lighten car structures – even back in the 1930s, some sports car makers were using aluminium, one of the lightest materials available and is still a popular material for low volumes speedsters and even some large luxury vehicles like the Audi A8 and Jaguar XJ.
As cars moved from the ladder chassis to a unitary construction, the body structure became a critical component. They started being manufactured with heavy steel and designers plus engineers looking to evolve into lighter designs and using better materials. The easiest solution was to use thinner steel, however better designs meant the strength could be improved as well.
The car industry has always worked alongside the aircraft industry thanks to the common technologies – aluminium was first used to make light but very strong fuselages. Then in the 1950s glass fibre was developed and started to be used for car bodies, however, glass fibre isn’t as strong as aluminium but is much lighter. In the event of an accident, glass fibre can split on impact – it did provide a basis for many track based race cars and low volume sports cars – even supporting big block V8s. Racing in the late 1950s through to the mid 1970s was a highly dangerous activity. We lost a huge number of drivers due to flimsy cars or design failures that caused big accidents.
The development of glass fibre lead to other composites like carbon fibre and Kevlar (owned by Du Pont). These materials were much stronger but very expensive to work with, especially as they needed to be cooked to cure them. The advantage was that the fibre mats could be moulded into many different shapes and thus could be made into more structural components. Often, composite structures use a sandwich of aluminium and carbon fibre for extra strength. Today carbon fibre is more common – companies are making after market panels for enthusiasts and high end cars are loaded with light carbon fibre panels.
The other important material that is used on ultra high-end cars is titanium. It is used as an alloy when used in car design. The important thing about all these materials is that they don’t corrode, although carbon fibre and Kevlar do have a shelf life – they lose their molecular structure over a very long time.
Engine manufacturers like Cosworth started to replace steel in their products with aluminium or titanium to reduce the weight of the conrods, pistons, flywheels and heads. Ancillary equipment were also lightened using these materials to further improve the power to weight ratio.
Finally, it is worth reviewing any spinning component on a car for lightness. I have spoken about the internals of an engine but what about wheels? My old Honda came from the factory with lightweight wheels and one way to get better performance is to lighten the wheels so that less energy is expended to turn them. You can even buy carbon fibre wheels for racing that reduce the weight still further.
On a recent car, I replaced worn brake rotors with lightweight ones as part of an upgrade of the whole braking system. Every little reduction helps although sadly I see perfectly good cars ruined by owners who think that they are making their cars faster by adding extra wings, large heavy wheels and the obligatory big bore pipes that do more damage than good for the performance.
Manufacturers spend a huge amount of time and resources to research materials and designs to improve their vehicles – especially to meet CAFE standards or to reduce the size of the motor needed to power the car. So if you want to have better performance or improved fuel economy, the same principles apply – lighten the structure so that less power is used to physically move the vehicle and as less power is needed, for those with economy in mind, you don’t need as much fuel.