Setups play an integral part in Assetto Corsa Competizione. Not only can a setup determine your overall pace, but it can also determine your consistency and race management throughout a stint. Finding that neutral balance in the setup is a key component of going quickly in ACC and it comes down to managing both oversteer and understeer tendencies.
Whilst we will explore solving understeer in a separate article, our focus today is offering you some tips to identify and solve oversteer.
What is oversteer?
“Oversteer is where a car rotates faster than the racing driver wants and results in the rear of the car becoming unstable.”
Simple right, so how do we rectify that?
There are a few key areas that you can focus on with rectifying oversteer in ACC through the setup. These main areas are:
There are a couple of the areas above which can be quite specific to a particular type of car. For example, front-engined and mid-engined cars will behave differently naturally. That is down to where the weight is situated within the car and therefore will promote certain tendencies. But let’s focus on the general rules of thumb we can apply in this article.
Ride height and Wing level
In ACC ride height is very important. Due to GT3 cars being very aero sensitive, you want to run the car as low as you can on the front to keep the centre of gravity as low as possible, without the risk of stalling the floor of the car or bottoming the car out over kerbs or big compressions.
Because of this, once you have settled on a good front ride height, focus then shifts to your rear ride height and balancing that with the wing level you are currently running on the car. When you raise the rear of a car in ACC you are shifting the centre of pressure forwards and therefore dialling more oversteer into the setup. This is because you are increasing the differential between the front and rear ride heights and this promotes an effect where the floor of the car isn’t being sealed as effectively as before. Whilst the area of low pressure is greater within the main diffuser area, the cars downforce production and operating window become peakier.
This then brings us onto the wing level you choose to run. Adding wing level to a car in ACC has the opposite effect of raising the rear ride height. By adding downforce to the rear of the car you are taking the centre of the pressure away from the front of the car, adding more force over the rear wheels in the form of aerodynamic load and therefore creating a more understeer biased car.
If you are encountering oversteer especially on entry, either increasing wing level or lowering the rear ride height will help make the car a more stable platform. Depending on how severe the symptoms are, one or the other might solve it, however, sometimes you will need to both add wing and lower rear ride height.
Generally, if you have a setup where the spring rates and dampers are to your liking, anti-roll bars can become a key component in shifting car balance to become more neutral front and rear.
One thing to remember about anti-roll bars, they do not directly generate or take away grip from a car, they simply alter how the load of the car is being distributed across the tyres during the cornering phase. The aim of anti-roll bars is to allow a driver to reach the cars optimum grip potential. Any deviation towards understeer or oversteer takes the car away from that.
With that in mind, how would anti-roll bars create oversteer and what do we need to do?
By stiffening the anti-roll bars you are making the car less susceptible to roll when the car is loaded up in the corner. This makes the car more responsive and therefore in some instances more nervous. If you find your car in ACC is nervous through the entry and mid-corner phase, there are a couple of things you can do with the bars to make it more neutral.
Stiffening the front ARB will mean the front of the car will roll less during the cornering phase. Because this, therefore, increases the roll stiffness and the weight transfer from one side to the other is controlled far more, the car will want to understeer more.
Alternatively, softening the rear ARB will do the opposite. In this instance, it will mean the rear of the car will roll more during the cornering phase. Because this, therefore, decreases the roll stiffness and the weight transfer from one side to the other is much slower, the car will want to understeer more.
When it comes to rectifying oversteer through spring rate changes, we need to be careful, as spring rates not only affect kerb handling/bumps but also control how a car pitches through acceleration and braking phases. Spring rates are an integral part of your setup, therefore any big changes will have knock-on effects through the whole lap.
With GT3 cars being so aerodynamically sensitive, your spring rates are directly linked to your ride height. Due to you wanting to run the ride height as low as possible, compromises need to be made with your spring rates to ensure the car doesn’t bottom out under pitching loads and compressions. This generally means you want to run them pretty stiff as a rule of thumb.
However, how stiff is very car-dependent and so we will keep this broad in spectrum. Softer spring rates will inevitably allow the car to pitch more forwards and backwards under big acceleration and braking phases, this is through the greater weight transfer the car is experiencing and this can lead to instability.
Front and rear spring rates also play a greater role in differing parts of the corner. If your springs are too soft on the front for example, under big braking loads, the front will pitch too much and therefore the rear will become unloaded very fast. This will promote oversteer on the entry to a corner as grip at the rear has been taken away under the pitching motion.
In this instance, stiffening the front spring rates will reduce the weight transfer to the front of the car and therefore decrease the oversteer on the entry/ braking phase.
When it comes to rear springs, running them too stiff can also cause oversteer. With a stiffer spring comes less load transfer and also less absorption of bumps and kerbs. This affects the car in a different part of the corner, most notably mid to exit. If you find the car you are driving in ACC too nervous at the rear under power or on exit kerbs in slower corners, it will generally mean your rear spring rate is too stiff. With less load transfer to the rear under power, there is less load pushing the rear of the car into the ground meaning a more nervous rear end.
With aero loads reduced in slow corners, mechanical grip plays a much bigger role in regards to rear stability and that is why you will encounter more issues with stiffer rear spring rates.
- Oversteer in fast corners: Stiffen front springs
- Oversteer in slow corners: Soften rear springs
- Oversteer under braking: Stiffen front springs
Bump stops can be used to mitigate the compromises that need to be with the spring rates. Think of the device as an additional cushion or shock absorber on top of the spring. In Assetto Corsa Competizione, not only can we determine how much travel the spring has before it hits the bump stops, we can also determine its stiffness through the rate. So how can we use these to help solve oversteer?
If you do not want to compromise on the spring rates in your setup, bump stops are a great way to control pitch and kerb handling. The way you can limit forward pitch under braking for example with bump stops is reducing the range of the bump stop before the spring hits it. This is a great way of running softer springs to aid kerb behaviour/bumpy tracks, yet not disrupting the aero platform of the car you are driving which would lead to instability, as the car isn’t allowed to pitch over a certain amount.
This can also be applied to the rear of the car. In some cars like the Porsche, where there is great weight over the rear wheels thanks to the engine, the bump stops can be used to limit oscillations at the rear under hard acceleration as the car pitches rearwards. For most cars, you want to run a very high rear bumpstop range at the rear. This is because hitting the bumpstops under hard acceleration regularly will cause the car to porpoise and therefore limit traction and create oversteer.
- Oversteer under braking: Lower bump stop range and soften the rate
- Oversteer in slow corners: Increase rear bump stop range
- Oversteer in fast corners: Lower bump stop range and soften the rate
Rear toe is a fantastic tool to use to fine-tune car behaviour once the rest of your alignment/suspension settings are to your liking. In Assetto Corsa Competizione, all cars run positive rear toe or what’s called toe-in.
Essentially, rear toe affects how quickly the car rotates during a corner. Greater rear toe will cause the loaded outside tyre entering a corner to start with a slight slip angle, meaning cornering forces are going to build up much faster. The loaded tyre is also going to reach maximum rotation much faster for the drivers given steering input creating a more stable platform during the cornering phase.
With the above in mind, if you are encountering turn in or mid-corner oversteer, increasing the amount of rear toe-in will help reduce it and take the car closer to an understeer bias. This, however, does come with the downside of added drag, due to the cars rear tyres being pointed inwards, which leads to an impact in straight-line speed.
On shorter or twisty circuits, the downside of the greater rear toe is outweighed by the advantages in the stability it provides, however on high speed or flowing circuits it might be wise to start elsewhere with reducing oversteer.
- Oversteer > Increase Rear toe > Lower straight-line speed
In ACC we have been given a simple differential with only one setting to adjust. Whereas in other sims we have diffs with preload, coast and power settings that can be adjusted, in Assetto Corsa Competizione we do not have to worry about that.
In that regard, the differential can be explained quite easily. The setting we are adjusting in the setup menu is the preload and indicates how early or late the differential opens up and then locks again. A greater preload figure will force the rear wheels to rotate at the same speed for longer before the diff fully opens up and gives the car more rotation on corner entry.
A lower figure will do the opposite, with the differential opening up earlier and allowing the rear wheels to rotate at different speeds far earlier into the corner. It will however lock up far later under power once you are at the exit of the corner. This means that traction is affected, as both rear wheels aren’t being forced to rotate at the same time as early as a higher figure selected in the setup menu.
Now we know the difference between them, we can understand how it will affect oversteer in different parts of the corner. In the entry to mid-phase of a corner, a lower diff setting will promote oversteer as the diff is trying to unlock far earlier, whilst the car is also trying to deal with the braking and turn in phases. The knock-on effect is the car will naturally want to pull itself around the corner far more with less steering input, also creating instability in some instances.
When it comes to latter parts of the corner, primarily on the exit when you are applying the throttle again, you may encounter oversteer due to your differential setting being too high. Whilst with a low diff setting you may encounter wheelspin on the exit, it won’t promote oversteer due to the wheelspin being caused by the inside rear tyre.
With a higher differential setting the oversteer is caused by both rear wheels being forced to accelerate together much earlier. This means on power, especially on worn tyres, a car with a diff setting too high can become snappy and unpredictable.
- Oversteer under braking/mid-corner: Raise differential preload
- Oversteer under power on exit: Lower differential preload
In Assetto Corsa Competizione, we have got 4-way adjustable damping available to us, broken up into rebound and bump in both slow and fast states. What dampers essentially do is help dissipate any vertical movement in the suspension and keep spring travel under control. This has a knock-on effect on helping keep the wheels on all 4 corners of the car in contact with the ground. Bump and rebound control both the compression and extension of the damper, they don’t directly control load levels received, but instead controls the speed of the load changes and ensure the suspension reacts in a stable manner.
Tracks that have more bumps or quick transitions and changes of direction require more emphasis on dampers. The quicker the suspension has to react and move to the circuit’s demands, the more effect the dampers have.
Because kerb handling and bump behaviour is very important on a lot of circuits in ACC, it makes sense to tune dampers to allow your car to take them effectively. However, going too far one way or another can lead to an unpredictable car.
So let’s quickly highlight what can happen if you go too far on both bump and rebound and how that can cause oversteer.
- Too much bump: Initial compression is very harsh > resistance to chassis roll
- Too little bump: Car will dive a lot > great weight transfer > lots of body roll
- Too much rebound: Tyres struggle to maintain contact on track surface > Inside wheels pulled away from the track surface
- Too little rebound: Car will oscillate for a long time after hitting bumps > Car will struggle for traction on the exit of corners
With the above in mind, we can deduct a few things and help solve oversteer utilising the dampers in a few scenarios. If you are encountering turn in oversteer, it could be that the slow bump setting on the front is far too soft, allowing for more pitch/dive and weight transfer than the tyres can cope with. Therefore increasing the front bump setting will help bring the car into a more natural state.
If you are struggling for traction on the exit of a corner, you may need to reduce your rear slow bump setting. This is because the initial compression under the longitudinal load of acceleration may be too harsh causing oscillations and therefore the tyres skate across the surface of the track.
The same can also be applied to rebound. Lowering the rear rebound will allow the rear wheels to settle quickly enough on the track and not hold them in the arches for too long under heavy braking phases. If not, the car will generate oversteer. Front rebound can also help corner exit oversteer. By Increasing the speed at which the front tyre settles on the track after the load has transferred rearwards, will allow the front of the car to bite earlier and promote a more understeer nature in the setup.
- Increasing front bump = More understeer
- Reducing rear bump = More understeer
- Increasing front rebound = More understeer
- Reducing rear rebound = More understeer
As you can see from the list above, in Assetto Corsa Competizione there is plenty of scope in the setup options to deal with and eradicate oversteer. Depending on how oversteer biased the setup is will determine how many solutions you adopt to get the car into a window that is comfortable for you.
Certain changes like spring rates and rear ride height will have a greater effect than tweaking tools like rear toe and the differential. That is true for cars too as some may require more changes and others less so. Use this article as a rough guide to understand the basics of rectifying oversteer and use the tips to make a nervous car a thing of the past for you in ACC.
If you’re looking for pre-built setups created by professional engineers and sim drivers, then take a look at ACC Setups.