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How to fix oversteer and understeer in ACC

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. 

In this ACC Setup Guide, we will be tackling both oversteer and understeer and providing you with tips to guide you in overcoming any challenges they may present to you.

What is oversteer and understeer?

“Oversteer is where a car rotates faster than the racing driver wants, and results in the rear of the car becoming unstable. Understeer is where a car rotates slower than the racing driver wants, and results in the front of the car sliding across the surface of the track.”

Seems fairly straight forward, but how do we use the setup parameters in ACC to rectify these problems?

There are a few key areas that you can focus on to rectify oversteer and understeer 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 naturally behave differently. That is down to where the weight is situated within the car and therefore promotes certain tendencies. 

But let’s focus on the general rules of thumb we can apply in this article.  

In most cases, it is always better to have an oversteering car than an understeering one. This is because a driver can much more easily influence how much oversteer they want the car to have corner to corner, whereas there is nothing you can do to reduce heavy understeer other than to over-slow the car a lot and wait for the front end of the car to grip up again. 

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.

To summarise:

Oversteer: 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. 

Understeer: If you are experiencing understeer, there are a couple of things you can do. To gain more rotation at slow speed it is generally best to raise the rear ride height up to the point where you feel the car is starting to be nervous on the transition from braking to turn in. That is generally the moment the floor is starting to feel the effects of not being sealed properly at low speed.

In higher speed corners when aero loads increase, you normally experience understeer if your wing levels are too high as the centre of pressure is too far rearwards. At this point the wing becomes a tweaking tool where you get the car into a window where it maintains good minimum apex speed whilst not being too safe and stable. 

  • Understeer in slow corners: Raise rear ride height
  • Understeer in high fast corners: Lower rear wing 
  • Understeer over the whole lap: Raise rear ride height and lower rear wing 

Anti-Roll Bars

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, is that 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 car’s 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 or understeer and what do we need to do? 

By stiffening or softening the anti-roll bars you make the car less or more susceptible to roll when the car is loaded up in the corner. Stiffening makes the car more responsive and therefore in some instances more nervous, while softening makes the car slightly less responsive, and therefore in most instances safer and more stable . 

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 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. 

Softening the front ARB will mean the front of the car will roll more during the cornering phase. Because this decreases the roll stiffness and the weight transfer from one side to the other is controlled far slower building the load up in the tyres progressively on the front, the car will then want to oversteer more. 

Alternatively, stiffening rear ARB will do the opposite. In this instance, stiffening will mean the rear of the car will roll more during the cornering phase while softening will mean the rear of the car will roll far less during the cornering phase . 

This therefore decreases the roll stiffness and the weight transfer from one side to the other is much slower, and so the car will want to understeer more. 

This therefore decreases or increases the roll stiffness, causing the weight transfer from one side to the other to be slower (more understeer) or faster (more oversteer).

Spring Rates

When it comes to rectifying oversteer or 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. Softening the front spring rates will, however, increase that weight transfer to the front of the car and therefore decrease the understeer on the entry/ braking phase as the rear of the car becomes unloaded far quicker. 

When it comes to rear springs, running them too stiff or soft can also cause oversteer or understeer, respectively. 

With a stiffer spring comes less load transfer and also less absorption of bumps and kerbs, while softening will give you more transfer and absorption. 

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.  

If you find the car you are driving in ACC too sluggish at the rear under power or on exit kerbs in higher speed corners, it will generally mean your rear spring rate is too soft. 

With less load transfer to the rear under power, there is less load pushing the rear of the car into the ground meaning a car that is more willing to rotate at speed. With aero loads reduced in slow corners, mechanical grip plays a much bigger role in regards to car behaviour. 

This is why front end bite on a stiffer front spring won’t be as strong and that is why you will encounter more issues with stiffer rates as opposed to a softer spring which loads up the tyre more and allows for more weight transfer.

To summarise:

  • Oversteer in fast corners: Stiffen front springs 
  • Oversteer in slow corners: Soften rear springs 
  • Oversteer under braking: Stiffen front springs
  • Understeer in fast corners: Stiffen rear springs 
  • Understeer in slow corners: Soften front springs 
  • Understeer under braking: Soften front springs/stiffen rear springs

Bump Stops

Bump stops can be used to reduce the compromises that need to be made 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 and understeer? 

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 with bump stops for example, 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. 

An example of the way you can promote forward pitch under braking to aid understeer with bump stops, is to increase the range of the bump stop before the spring hits it. This is a great way of running stiffer springs to aid stability within the aero platform, yet not running into the bump stops too early so that the car oscillates and bounces back causing understeer which would lead to instability, as the car isn’t allowed to pitch over a certain amount. You are essentially giving the spring more room to breathe. 

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 bump stop range at the rear. This is because hitting the bump stops under hard acceleration regularly will cause the car to porpoise and therefore limit traction and create oversteer. 

It can create understeer however, as the rear spring receives the weight transfer under acceleration and unloads the front tyres too much. By limiting the spring travel on the rear by reducing the bump stop range, it can be a method of reducing exit understeer. 

To summarise:

  • Oversteer under braking: Lower bump stop range and soften the rate
  • Understeer under braking: Increase front bump stop range and stiffen the rate
  • Oversteer in slow corners: Increase rear bump stop range 
  • Understeer in slow corners: Lower rear bump stop range
  • Understeer in fast corners: Increase front bump stop range and stiffen the rate 
  • Oversteer in fast corners: Lower bump stop range and soften the rate 

Rear Toe

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. 

Rear toe essentially 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 a negative impact on 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 when reducing oversteer. 

If encountering turn-in or mid-corner understeer, decreasing the amount of rear toe-in will help reduce it and take the car closer to an oversteer/neutral bias. In addition, the decrease does come with the upside of less drag due to the car’s rear tyres being pointed inwards far less than before, leading to a positive impact on straight-line speed.

Again, in the case of shorter or twisty circuits, the benefit of lower rear toe can be most felt in initial rotation or quick direction changes. However it will have to be managed as you can quickly overheat rear tyres or cause blistering in hotter temperatures due to too much wheelspin. The key here is to reduce the rear toe enough so that you are on the verge of encountering that wheelspin but retain enough rotation to eradicate the understeer. 

To summarise:

  • Oversteer > Increase Rear toe > Lower straight-line speed
  • Understeer > Decrease Rear toe > Increase straight-line speed

Differential

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 and understeer 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. A higher diff setting then promotes understeer as it tries to unlock far later while also dealing with braking and turn-in. 

The knock-on effect of a lower diff setting is that the car will naturally want to pull itself around the corner far more with less steering input, also creating instability in some instances. A higher diff setting will cause the opposite and want to pull the car around the corner a lot less, whilst requiring more steering input, creating an unresponsive front end. 

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. 

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. 

If your diff is set too low, you may encounter understeer instead. A high diff setting may cause you to encounter slight wheelspin on the exit, but won’t promote understeer due to the wheelspin being caused by the inside rear tyre. 

Both rear wheels not being forced to accelerate together earlier causes understeer when running a lower differential setting. A car with a diff setting too low can become unresponsive when exiting corners on power, especially when on worn tyres.

To summarise:

  • Oversteer under braking/mid-corner: Raise differential preload 
  • Understeer under braking/mid-corner: Lower differential preload 
  • Oversteer under power on exit: Lower differential preload
  • Understeer under power on exit: Raise differential preload

Front and Rear Damping

In Assetto Corsa Competizione, we have g4-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 control 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 or understeer. 

  • 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 and understeer utilising the dampers in a few scenarios. 

Oversteer:

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.  

Understeer: 

If you are encountering turn-in understeer, it could be that the slow bump setting on the front is far too firm, allowing for not enough pitch/dive and weight transfer, meaning the front tyres want to scrub across the surface of the track. Therefore increasing the softening the front bump setting will help bring the car into a more neutral state. 

If you are struggling for rotation on the exit of a corner, you may need to increase your rear slow bump setting. This is because the initial compression under the longitudinal load of acceleration may be too much, leading to the car pitching rearwards and therefore the front tyres become unloaded far quicker. 

The same can also be applied to rebound. Increasing the rear rebound will allow the rear wheels to settle more slowly on the track and hold the rear tyres in the arches for a little  longer under heavy braking phases. This will eradicate understeer and bring the car closer to an oversteer bias. Front rebound can also help corner exit understeer. By lowering 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 less, meaning the overall grip percentage front to rear increases.  

To Summarise:

  • Increasing front bump = More understeer
  • Reducing rear bump = More understeer
  • Increasing front rebound = More understeer
  • Reducing rear rebound = More understeer 
  • Decreasing front bump = More oversteer 
  • Increasing rear bump = More oversteer
  • Decreasing front rebound = More oversteer
  • Increasing rear rebound = More oversteer

Summary

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 both oversteer and understeer.

Depending on how oversteer/understeer 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 understeer, and make use of the tips to make a nervous or safe and predictable car in ACC a thing of the past.

If you’re looking for pre-built setups created by professional engineers and sim drivers, then take a look at ACC Setups.

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