DiRT Car Setup Guide
basics

 

Suspension stiffness
This obviously sets up how hard the car's springs are. In general these should be increased and decreased in proportion to each other, unless the car lacks an anti-roll bar at one or other end. an overall stiffer car will have more grip on smooth surfaces because it will roll less. it will lose grip on uneven surfaces, though as the tyres wuill find it harder to maintain contact.

Ride height (overall)
how high the car is from the road. or to put it another way, how much movement you want to allow the suspension to have. stiffer cars can run lower, and soft cars require a higher ride height to avoid grounding and hitting the bump-stops. really this setting and suspension stiffness go hand-in-hand.

Final Drive ratio
Basically this wants to be set as low as can be done without the car hitting the Rev Limiter in the top gear - this maximises the available acceleration.

Brake Bias
This affects the understeer/oversteer balance under braking. having this set towards the front will give you a stable car under braking which will tend to go in a straight line. moving this towards the rear will increase instability making the car easier to provoke into oversteer

Central Diff Torque Split
This essentially acts like Brake Bias, but for power- set this forwards for stability and understeer, and to the rear for power oversteer.

Downforce
The most fundamental tradeoff - straightline speed against speed in the turns. Low downforce will give you a fast car that won;t have much grip - high downforce gives you a grippy car that may be sluggish on straight sections.

Anti-Roll Bars (front / rear)
ARBs are the primary tool for tweaking the car's balance in the turns. They act like the main suspension stiffness, but only come into play when the left and right wheels at each end of the car want to be at different heights relative to the body.
As a general rule, a stiffer ARB at a given end will cause that end to have less grip- or rather will make it more likely that it will run out of grip first.
So a car with a soft front end, with a hard back end will tend to oversteer, and a hard front end with a soft back end will tend to understeer.

ARB settings are often used to correct the natural handling balance of different drivetrains bacuse they are a very powerful tool.
The soft front/hard back is common in Front-wheel-drive cars bacuse of the natural tenency they would have otherwise to understeer. you can see this in action if you look at pics of hot hatches and FWD touring cars being driven hard where you can see them "cocking a leg" and lifting the inside rear wheel in the air.
Similarly, powerful rear-wheel drive cars tend to run with a stiff front ARB and soft at the rear.

Camber
camber describes the ange of the wheel in relation to the car, looking from the front or the back. most racing and rally cars run with a certain amount of Negative camber, where the bottom of the wheels is further apart than the top of the wheel.
This is important because the whole point of car setup is making sure the tyres are giving the most they can guvem the most of the time, and tyres give the most they can when they;re flat to the surface of the road. (this isn't entirely true but it severs for now and we'll come back to this point later)
when the car is in a turn, the body rolls- anti-roll bars combat this to a degree but it's undesirable to run the car so stiff it won't roll at all.

As the body rolls, so do the tyres (this makes an assumption about suspension geometry that isn't, again, entirely true, but it serves). is the tyre is perfectly flat to the road when the car's not turning, the tyre will start to push onto it's edge. what we want, then, is for the tyre to be flat to the road when we need it most, when we're turning. so this is what the negative camber acheives, but angling the wheel, it's at the right angle when we need it most.

What this doesn;t take into account is an affect called "camber thrust" which basically means that in real life the optimum angle for the tyres when cornering is still angled in a little bit when the car's turning because it pushed the car sideways a bit.

Toe
Toe describes the angle of the wheels relative to each other looking down on it. essentially, it's a stability control. pairs of wheels that are toed-in lend stability to that end of a car, and pairs of wheels that are toed-out make it unstable. there is also a small straightline speed penalty, as toed wheels are moving along the road slightly sideways when the car is driving in a straight line. if you're having difficulty with turning the car into hairpins, toe-out on the fornt wheels can help. if the car's wandering over the road when you want it to go straight, try toeing the front wheels in. at the rear, a touch of toe-in can help tame an oversteering car. it;s generally not considered a good idea to toe-out the rear wheels as this can make the car very unstable.

Dampers
Damper adjustment is a hard thing to put into words. in basic terms the damping strength is somethgni that needs to rise and fall in line with spring stiffness - harder springs require stronger dampers. adjusting them on their own producing an effect simliar to that of adjusting suspension stiffness, but where they're really effective is in tweaking the car's behaviour in transitions- turning into the corner and coming out. once the car' settled into a turn, the dampers should be doing less work.

Rebound damping should usually be set at around 2/3rds of bump.

Fast bump - "fast" in this case is referring to vertical wheel speed, not the car's speed. what this adds is the capbility to have extra damping force applied when the wheel is moving very fast upwards (landing from a jump, for example. or on rough surfaces) without too much compromise on handling (where wheel speeds are generally slower). Activation sets the level at which you want this effect to cut in.

brake size
by varying your brake size and pad hardness you can effect changes to the strength and bite of the brakes.

Individual gear ratios
This isn't something that generally needs changing uinless in very specific circumastances. if, for example, you're on a track that has very few low-speed turns (and you've got the final drive set right), then it can be advantageous to move all the gear ratios towards the final drive, so the car can be working in its power band for longer. simlarly, a track with lots of hairpins, but also a very long straight, can benefit from having the ratios mostly low, but with a long top gear for the straight.

Thanks to Rich Tysoe from Codemasters

 

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