As standard, most chassis are designed to meet a minimum set of requirements at a reasonable price - as such, there are usually improvements that can be made for vehicles that are going to be used for heavy duty applications and racing.

Material Choice

  If possible, one of the best ways to improve upon a design is to ensure that the most suitable materials are being used. Steel, for example, is available in various grades, and rebuilding a chassis using a higher grade will give strength benefits - In drag racing, the chassis of a competing vehicle must be built from a minimum grade of metal in order to run in certain classes.

  Another good example of this is in tubing; the cheapest way to make tubing is to take a flat sheet of metal, roll it into shape, and then weld the seam (such tubes are referred to as electrical resistance welded, or ERW - the picture on the left shows a machine used to do this on an industrial scale). However, this seam can be a weak point, and so extruding out a tube in one (seamless) piece is preferable. Given that most of the time, a space frame chassis is built for a specialised purpose, seamless tubing will be used, this is more relevant when building additional components such as rollcages (below).

  Remember - as we said in the section on chassis materials, completely different materials cannot be interchanged without redesigning the structure to suit their different properties. A steel chassis rebuilt to exactly the same specifications from aluminium or titanium will be far lighter, but much more susceptible to flexing.

Bracing

  Additional bracing can be fitted to stiffen up a chassis, and to reinforce things like mounting points. During the sixties, the sports versions of Ford Escorts used different bodyshells to the regular versions, with the addition of small reinforcement panels at critical points. These not only made the shell stiffer, but also strengthened it with a view to competition use.

  Tubular bracing is often used to triangulate across areas of the chassis that have been left open to allow for other components - engine bays etc. A common modification to monocoque bodyshells is to run a brace between the tops of the suspension mounts, to prevent flexing.

  Again, this is not because of any inherent inadequacies with the original design, but due to the fact that a chassis is designed with a balance between cost and performance - a balance that changes depending on whether you are dealing with a family hatchback or a sportscar. Additional bracing adds cost, and can also reduce practicality (access for servicing, for example), and so if you can get away without it, it's generally not included on a production model.

  Care needs to be taken when designing extra bracing that it does not cause loads to be transferred onto points that aren't designed to cope with the forces involved. As such, most bracing runs between points that are already load-bearing, and uses plates to spread the loads where required.

Rollcages

  A rollcage is basically a space frame chassis designed with protection in mind, which is retro-fitted to an existing chassis primarily for added reinforcement in the event of a roll-over or other serious accident. Rollcages (properly referred to as "roll-over protection devices") vary from a simple bent tube behind the driver's seat to a fully welded-in frame mounting to a dozen or more points on the car.

  Properly-designed rollcages also give the same stiffening advantages as fitting bracing, and are often linked up to suspension mounting points etc. The rollcages fitted to a professional rally or touring car offer enough reinforcement to render the original monocoque almost obsolete.

  For racing use, regulations will often state that an rollcage of certain minimum specifications is required, and professionally-built cages are usually made to meet a given set of regulations. As a minimum, it is usually required that the cage be manufactured from seamless tubing, with a specific thickness and grade of metal.

  The safety benefits of rollcages should not be underestimated - many drivers, including celebrities like Colin McRae, owe their lives to them, and if you've ever seen the mess that a high-speed crash can make of a bodyshell, it's easy to understand why they are insisted on for competition.

Welding Improvements

  As most bodyshells are manufactured by spot welding the panels together, a simple way to stiffen them up is to either stitch or seam weld them instead. As with welding during construction of a chassis, care must be taken to avoid problems due to excessive heat.

  Normally, additional welding is concentrated on specific areas, such as suspension mounting points or the engine bay, as it is quite a labour intensive technique. Most of the time, a full rollcage would be fitted instead of additional welding, but in some instances where a cage is not going to be used, full welding of the entire shell can take place.

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