Race Car Setup Reference Manual (For Video Games)

Forza Horizon 4 is being released tomorrow (for Ultimate Edition owners), so while I endure this endless wait, let's look at how to setup your car, except we are actually going to look at the Assetto Corsa Competizione setup page because I can't actually see the FH4 page (it's probably better anyway). This is also the first post I've put in the engineering tab after the 5 months that this blog has been active. Neat.

Tyres

PSI

Softer tyres have a larger surface area which improves traction at a cost to responsiveness in high load situations. Increasing tyre pressure can very slightly improve straight line speed, but also creates higher tyre temperatures.

Toe

The toe angle identifies the exact direction the tires are pointed compared to the centerline of the vehicle when viewed from directly above. Toe is expressed in either degrees or fractions-of-an-inch, and an axle is said to have positive toe-in when imaginary lines running through the centerlines of the tires intersect in front of the vehicle and have negative toe-out when they diverge.

A primary purpose of adjusting toe is to alter how the vehicle responds to the initial steering input. Setting the front wheels with toe out will provide the vehicle with a sharper turning response at the expense of front stability.

Rear toe-in causes the more heavily loaded outside tire to start with a slight slip angle so the buildup in forces are going to start sooner and the maximum yaw for a given amount of steering will be less. For both of these reasons the car will feel more stable during cornering.

Camber

The camber angle identifies how far the tire slants away from vertical when viewed directly from the front or back of the vehicle. Camber is expressed in degrees, and is said to be negative when the top of the tire tilts inward toward the center of the vehicle and positive when the top leans away from the center of the vehicle.

Adjusting the camber angle will change the tyre contact patch with the track surface, where adding negative camber can improve lateral grip in sustained cornering situations, at a cost to longitudinal traction.

Electronics

TC

Traction control (TC) limits wheel spin under power. Higher levels give more intervention resulting in a more stable car but potentially slower lap times.

ABS

An anti-lock braking system (ABS) keeps the wheels from locking under heavy braking. Higher levels equals more intervention, better positioning under braking, but longer braking distances.

Grip

Anti-Roll Bars

Anti-roll bars don't directly add or take away grip; they simply shift how the load is distributed among the tires during cornering. This causes a balance shift because of a tire's load sensitivity. Stiff anti-roll bars will reduce the amount of body roll while turning into corners, but will put the tyres under excessive loads during prolonged corners. Soft anti-roll bars provide good traction throughout prolonged corners at a cost to initial responsiveness.

Brake Power/Bias

Brake pressure determines the maximum potential breaking power of the vehicle. Although an increase in brake pressure can result in shorter stopping distances, depending on the amount of ABS, it will be far easier to lock up.

Brake bias indicates the relative amount of brake pressure applied to the front brakes. E.g. 52% would indicate that the front brakes were receiving 52% of the brake pressure and the rear brakes would be receiving 48%. Brake bias adjustable from the cockpit in GT3 cars and is used to maximize braking potential and control vehicle balance while using the brakes. Setting brake bias to the front increases the chances of front lock ups, causing understeer on corner entry, whereas rearward bias has the opposite effect.

Steering Ratio

The steering ratio is the ratio of the number of degrees of turn of the steering wheel to the number of degrees the wheel turn as a result. A higher steering ratio means that the steering wheel is turned more to get the wheels turning, but it will be easier to turn the steering wheel. A lower steering ratio means that the steering wheel is turned less to get the wheels turning, but it will be harder to turn the steering wheel.

Wheel Rate

Wheel rate is the spring rate (amount of weight it takes to compress a spring a certain distance) but measured at the wheel instead of where the spring attaches to the chassis. Higher wheel rates will stop the car from lunging forward during aggressive breaking or rearward under sudden acceleration. While this improves aerodynamic stability, it can be very harsh on tyres as well as skittish over bumps. Lower rates absorb bumps more effectively, but harsh acceleration or breaking can pivot the vehicle aggressively, lowering stability.

Dampers

A part of a car's suspension designed to reduce oscillations and modify the dynamic movement of the car. Also known as a shock absorber. Race-oriented dampers may have separate adjustment for compression (bump) and extension (rebound). Dampers can be configured in slow speeds (slow body movements; in roll, pitch and squat), as well as fast speeds (fast suspension movements when going over bumps, kerbs, and similar undulations of the surface). In general, to improve road holding over bumps you will want to soften dampers up to the point that you get no more than one oscillation after a big bump. This means that the car goes to full compression during a bump, and then it can go to full extension before finally settling back to its normal ride height.

Aero

Ride Height

This is the static or dynamic measure of a car chassis in relation to the ground. It is usually measured from the lowest points on the car that will make contact with the ground first if the ride height is too low. Lowering the ride height will lower the center of gravity (CG) which reduces load transfer and increases grip. The lower the CG the faster the car will be, however at some point the car will start having issues with bottoming out on the track or start having issues with suspension.

Rear Wing & Splitter

Higher wing/splitter angle with create more downforce, allowing a car to travel faster through a corner by increasing the vertical force on the tires, creating more grip, but at a cost to more drag which reduces straight line speed.