Everything on a racing car affects something else. Nothing works in isolation, and understanding the complex systems and links between the systems is crucial to engineering a winning car.
I've discussed before how compromise is needed to win races. That having an optimal overall system is more important and optimising each system on its own. But within those systems, you have often unseen and not so obvious links that can have a detrimental effect on the overall package.
I'll use a few examples to show you what I mean:
Most modern racing cars will have the ability to alter the engine map depending on driver preference and prevailing track conditions. This usually involves altering ever so slightly how power is delivered, however some championships may allow for more than this. There are situations where more aggressive, higher power engine maps are used during qualifying for example. These maps put a huge strain on the engine, but are only used for a relatively short period of time.
What is often overlooked is how these engine changes will affect the traction. A driver may complain that they cannot use the power when they want to out of corner, and so a less aggressive map will be used. However this will reduce the slip ratio for the driven axle, potentially inducing understeer.
Worse than this, your chassis engineer may decide that the issue of corner exit traction can be rectified through kinematic and geometry changes. If both chassis and engine changes are made, you can easily end up going too far and ruining the overall balance or making the car sluggish.
Changing ride heights is one of the fundamentals of setting up a race car. It will have a direct effect on the roll center of the car, and as such a dramatic effect on the handling. It is something that is usually something that can be changed quickly, and often by only a few millimeters (See Small Changes).
However the ride height does not act in isolation.
Changing ride heights will have an effect on the suspension kinematics; the way the wheel is controlled and moves under bounce and rebound. If this is not taken in to consideration when the ride height change is made, the results can be unexpected. Now most race cars will have adjustable everything on each wheel - camber, caster, toe, K, etc. - but if they are not changed in a systematic and controlled way, you can spoil the balance and handling of your car.
Another often overlooked effect of ride height changes is the affect it can have on the aerodynamics of the car. A car running a little too high or a little too low can be comes unstable and even dangerous. Adjustable splitters, diffusers and wings are there to accommodate changes where necessary but there is often a limit to what can be done.
Tyre Pressure Changes
Yes, even the simplest of changes to make can have knock on effects to other areas of the car. The tyres can be thought of as a spring, and they do play a crucial role in the spring rate of a wheel system as a whole. The entire system (from contact patch to chassis mount) has a spring rate that is known as the "Wheel Rate". Changing the tyre pressure will change this value.
To a degree, tyre pressure changes can be tolerated by the suspension system. Plus or minus a few tenths of a bar won't have dire consequences. But if you start playing around with larger pressure changes, you will fall in to a trap of chasing ghost springs in your system.
I have also seen cases where tyres were calibrated using nitrogen, but run using compressed air. The difference in Gas Constant meant the tyres were completely out of kilter with where they were expected to be. They came back from a run massively overheated and over inflated.
Before committing to a change on a car, think carefully about where the change will have an effect. What other systems might be altered by your change? How can the changes be negated or accommodated?
Compromise wins races. But knowledge definitely helps.
Tom is an engineer working his way through the motorsport industry, sharing stories, anecdotes and lessons to help new engineers coming through the ranks.