Basic settings | Rally car configuration CMR: DIRT Guide

Last update: 11 May 2016

Suspension Springs

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. So, when competing on tarmac, the stiffest setting possible should be used to keep the body roll of the vehicle to a minimum. By reducing body roll the car is able to change direction quicker, allowing the driver to take corners at higher speeds.

On gravel and mud surfaces a softer suspension is used. This allows the suspension to absorb the impacts of the rough road surface preventing damage to the chassis of the vehicle. Softer suspension also allows the vehicle to gain better grip on the loose surfaces.

Altering the spring rate affects the pitch of the vehicle also. A softer spring rate will let the vehicle pitch forward under braking and back under acceleration. Adjusting the front and rear settings independently will allow you to achieve a better balance to suit your driving style.

Ride Height

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. Ride height is of great importance in off road racing.

When competing on tarmac a low ride height should be used to give the vehicle a low centre of gravity and stability as it travels through tight yet high-speed corners. Care should be taken not to set the ride height too low as you run the risk of bottoming out.

When heading off road and onto the looser surfaces the ride height should be raised to allow greater travel in the suspension. This will allow the vehicle to handle uneven road surfaces at speed and manage jumps better.

Really this setting and suspension stiffness go hand-in-hand. Stiffer cars can run lower, and soft cars require a higher ride height to avoid grounding and hitting the bump-stops.

Summary: for smooth surfaces (tarmac for example) you should choose harder suspension and low ride height. For loose surfaces (mud, sand): softer suspension and high ride height.

Brakes

Brake Bias

Setting the brake balance toward the front of the vehicle will give the vehicle a tendency to understeer, however, it will help the vehicle slow down faster on tarmac surfaces when braking in a straight line.

Setting the brake balance to the rear of the vehicle will give the vehicle a tendency to oversteer under braking. This can be useful when using left foot braking (rally technique) to drift the car around loose surface corners.

Check your car's drive train to better match the distribution of braking force. However, pay attention that strong shift of braking force will increase the danger of blocking the given axle when braking hard and violently.

Brake Set

Small discs should be used on stages where less braking is required because they disperse heat slowly, allowing the brakes to retain the correct temperature and hence function at full efficiency. Large discs will need to be used for stages involving lots of braking, as they help disperse the heat, reducing the chance of warping and damage.

Differentials

Central diff

In other words - the drive balance (also known as drive bias). In four wheel drive vehicles a slider will allow you to adjust what percentage of the drive (how much of the engine's power) goes to the front and rear wheels.

This essentially acts like Brake Bias, but for power: set this forwards for stable and understeer car behaving more like a front wheel drive vehicle when the throttle is being applied mid-turn, and to the rear for power oversteer if you want an oversteering car behaving more like a rear wheel drive vehicle when accelerating and turning.

Limited Slip Diffs

Adjustments to the limited slip differentials will dramatically affect the vehicle's handling characteristics. In four wheel drive vehicles you can adjust the front and rear differentials independently.

By increasing the strength of the differential under acceleration, the traction will be increased when exiting corners. This is because the differential will prevent the inside wheel from spinning. Increasing the strength of the differential under deceleration will make the vehicle more stable under breaking and give the vehicle a tendency to understeer.

It is worth noting that a strong deceleration setting will make the car difficult to steer and is recommended only for drivers with a late braking driving style.

Downforce

This determines how the air flows around the running vehicle.

High downforce settings will push the vehicle down onto the road at high speeds. This extra grip allows the driver to take corners faster but reduces the car's top speed due to the added wind resistance. It's proper to increase the downforce on tight and twisty tracks.

On fast open stages it can be advantageous to reduce the downforce so that the vehicle is able to obtain a higher speed, however, this will reduce the cornering speeds as the car will become more unstable. Similarly to the long gearing, also low downforce proves correct on tracks with long straights.

Anti-roll bars

Sometimes known as stablilisers, the anti-roll bars are an additional way of improving the responsiveness of the vehicle when taking corners, of tweaking the car's balance in the turns.

A stiff anti-roll bar setting will suppress the body roll of the vehicle and allow the momentum to shift quickly. A soft anti-roll bar will allow more body roll and prevent the vehicle from bouncing on a stiff suspension set up.

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 because they are a very powerful tool. The soft front/hard back is common in Front-wheel-drive cars because of the natural tendency 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.