AUGUST 2019 ISSUE
How many times has the driver been heard to say “we missed the set-up today” when trying to explain away a poor performance? Sometimes you will have heard him say “we are chasing the set-up”, or perhaps even “we got the right set-up on the car today.”
What is this mysterious ‘set-up’ that the driver is referring to? And how is it so influential on a racing car’s performance? In this three-part tech talk series, we are going to try and de-mystify and explain this famous phrase ‘set-up.’
In simple terms, the set-up starts with basic suspension alignment where the front and rear wheels are set relative to each other – this is referred to as ‘setting the toes.’ Typically, the front wheels will run 2mm toe-out and the rear wheels will run 2mm toe-in. This differs from a road car only on the front axle, where a road car setting would generally be toe-in (just like on the rear axle). If you are a Lexus owner, the service department of your local dealer would perform this check and adjustment very quickly by altering adjustable links in the front and rear suspension to give the required setting.
The next setting is the front caster. Caster is very much as the term says, and just like a caster wheel on a piece of furniture it gives the car some stability when in motion. Again, road cars are very similar in this respect.
In terms of alignment, the final setting is the front and rear cambers. The camber of a wheel is the angle it presents itself to the road surface when the car is viewed head on. If the tops of the wheels are leaning into the center of the car, that is referred to as ‘negative camber’, whereas ‘positive camber’ is when the tops of the wheels are pointing away from the center of the car. In GT racing the camber is always set ‘negative’. The question is how much ‘negative camber’ should be applied to the car. To determine this, Michelin—the tire supplier for the Lexus RC F GT3 car—provides data to help the engineers decide. Typically, the front camber will be set to around -3 degrees and the rear camber will be set to around -2 degrees. Once running, Michelin engineers measure the surface temperature of the tires each time the car stops in practice and provide advice to the car engineers should any adjustment be required.
In next month’s tech talk, the second-piece of this three-part series on set-up of the Lexus RC F GT3, you will learn about the importance of determining the ride height of the race car.