Mechanical Grip

Anti-Roll Bar

What It an Anti-Roll Bar?

An anti‑roll bar, often C‑shaped and made from a solid or tubular metal rod, links the left and right suspension systems on the same axle. In simple terms, it’s a torsion bar that resists differences in suspension movement between the two wheels.

When one wheel’s suspension compresses and the other extends (as happens during cornering), the bar twists to limit the difference in travel. This reduces body roll and helps keep the car balanced.

Anti‑roll bars don’t directly create or remove grip, instead, they redistribute load between the tires during cornering. By fine‑tuning this load transfer, they can shift the car’s handling balance toward understeer, oversteer, or a more neutral setup, helping the driver reach the car’s maximum grip potential.

Anti-Roll Bar Function

As the name suggests, the primary role of an anti‑roll bar is to reduce body roll and improve stability in corners. It works by transferring some of the force from the less‑loaded suspension to the more‑loaded side, keeping the chassis flatter and more composed.

A stiffer anti‑roll bar also helps maintain suspension geometry, particularly camber, under load. This means the tires keep their intended contact patch and angle relative to the road, even during aggressive cornering.

Roll Bar Effects

Stiffer Anti‑Roll Bar

• Tires warm up more quickly

• Higher peak tire temperatures

• Sharper, more precise handling, but potentially more nervous at the limit

• Easier recovery if stability is lost

• Reduced compliance over bumps or in wet conditions, which can make the car harder to control

Softer Anti‑Roll Bar

• Tires warm up more slowly

• Lower peak tire temperatures

• Increased body roll, which can improve grip on uneven or low‑grip surfaces

• Smoother, more forgiving handling, but with less immediate steering response

• Better compliance over bumps, curbs, and in wet conditions, improving stability

Anti-roll Bar Adjustment

Adjusting anti‑roll bar (ARB) stiffness changes how much the car resists body roll when loaded in a corner. If your car feels nervous through corner entry or mid‑corner, ARB adjustments can help bring it back toward a neutral balance.

• Stiffening an ARB makes the car more responsive, but can also make it more nervous at the limit

• Softening an ARB reduces responsiveness slightly, but generally makes the car more stable and forgiving

Front Anti‑Roll Bar

• Stiffening the front ARB reduces front body roll, increases roll stiffness, and transfers weight more quickly across the front tires. This typically increases understeer

• Softening the front ARB allows more front roll, reduces roll stiffness, and transfers weight more gradually. This builds load on the front tires more progressively, often increasing oversteer due to the change in front‑to‑rear load distribution

Rear Anti‑Roll Bar

• Stiffening the rear ARB reduces rear body roll, increases roll stiffness, and transfers weight more quickly across the rear tires. This generally increases oversteer and can make the car feel more nervous

• Softening the rear ARB allows more rear roll, slows weight transfer, and typically increases understeer

Balance Considerations

• A much stiffer front ARB compared to the rear will promote understeer, making the car reluctant to rotate into corners

• A much stiffer rear ARB compared to the front will promote oversteer, making the car easier to rotate but potentially unstable

• Important: Excessively softening the rear ARB or excessively stiffening the front ARB can both lead to understeer 

• Choosing the right adjustment depends on tire temperature data and how the car behaves on track.

When ARB Changes Are Most Noticeable

• During steady‑state cornering

• After initial turn‑in and before corner exit

• When the car has settled into its roll angle

Roll Bar Effects

Front anti-roll bar

• Has a greater impact on cornering behavior than the rear ARB

• Soften to correct understeer in corner entry

• Stiffen it to correct oversteer at corner entry

Rear anti-roll bar

• Has a greater impact on throttle behavior than the front ARB

• Soften to correct oversteer in corner exit

• Stiffen to correct understeer when exiting corners

Differential 

The differential is the mechanical system that manages the rotational speed of each driven wheel. In GT cars, it allows the inner and outer wheels to rotate at different speeds, essential in cornering, since the outer wheel must travel a longer distance and therefore rotates faster than the inner wheel.

GT3 Regulations

In GT3 racing, the degree of differential lock under acceleration and deceleration is fixed by homologation rules. The only adjustable parameter is preload.

Preload Explained

Preload is an adjustable spring force inside the differential that influences how much torque difference is allowed between the two axle shafts before the diff begins to unlock or lock.

• Higher preload: Rear wheels stay locked together for longer before unlocking. This can increase stability but reduce rotation on corner entry

• Lower preload: Diff unlocks earlier, allowing the rear wheels to rotate at different speeds sooner. This can increase rotation but reduce stability

Preload Characteristics

Preload only influences the car during acceleration or deceleration (when the throttle is being pressed or released)

The effect varies with corner type:

• Slow corners (low gear, high RPM)

  • Low preload: Agile and stable on release/braking; less traction and slight understeer on acceleration

  • High preload: Understeer on release/braking; more traction and oversteer on acceleration
    
    

• Fast corners (high gear, low RPM)

  • Low preload: Agile and stable in both release/braking and acceleration phases

  • High preload: Understeer in both release/braking and acceleration phases

Preload Effects

Corner Entry to Mid‑Corner

• Lower preload:

  • Promotes oversteer as the diff unlocks earlier during braking and turn‑in

  • Car rotates more easily with less steering input but may feel unstable
    
    

• Higher preload:

• Promotes understeer as the diff stays locked longer during braking and turn‑in

• Car requires more steering input and may feel less responsive at the front

Corner Exit Effects

• Higher preload:

  • Can cause oversteer on throttle, especially on worn tires, as both rear wheels are forced to accelerate together earlier

  • May feel snappy and unpredictable under power
    
    

• Lower preload:

• Can cause understeer on exit because the rear wheels are not locked together early enough

• May feel unresponsive under power, particularly on worn tires

Wheel Rate

Wheel rate, also known as spring rate, is the amount of force required to compress the suspension through its full travel. In setup terms, it refers to the stiffness of the springs fitted to the car.

Because every car has a different overall weight and weight distribution, spring stiffness must be tailored to the specific chassis. For example, a front‑engine GT3 car will naturally require stiffer front springs than a mid‑engine car due to the extra weight over the front axle.

Why Spring Rate Matters

In GT3 racing, where cars are highly aero‑dependent, spring stiffness plays a major role in keeping the aerodynamic platform stable. Spring rates also directly influence ride height, which in turn affects aero performance.

Running the ride height as low as possible is desirable for aero efficiency, but springs must be stiff enough to prevent bottoming out under braking, acceleration, or heavy compression. As a rule of thumb, GT3 cars tend to run relatively stiff springs, but the exact stiffness is car‑specific.

Adjustment Approach

Spring rate changes should be made in small increments to properly feel their effect on handling and power delivery, large changes can have knock‑on effects throughout the lap.

Springs influence far more than just cornering balance, they also affect:

• Kerb and bump absorption

• Pitch control under braking and acceleration

• Weight transfer characteristics

Bumpstop 

Purpose in GT Cars

GT cars rely heavily on aerodynamic devices, wings, diffusers, splitters, to generate downforce.

Under braking, the car pitches forward:

• Front splitter moves closer to the ground: increases front downforce

• Rear diffuser rises: reduces rear downforce

This shift in aero balance toward the front can make the car unstable if not controlled.

What is a Bumpstop?

A bumpstop is a rubber‑like insert positioned above the damper that limits suspension travel. Think of it as an extra cushion or secondary spring that engages when the main spring compresses to a set point.

Two key parameters define bumpstop behaviour:

• Range – How much suspension travel occurs before the bumpstop engages

• Rate – The stiffness of the bumpstop once engaged

Bumpstops allow you to fine‑tune pitch control and curb behavior without compromising spring rates.

Using Bumpstops for Balance

• Limiting forward pitch under braking:

  • Reduce bumpstop range at the front so it engages earlier 

  • Lets you run softer springs for curb/bump compliance while keeping the aero platform stable
    
    

• Promoting forward pitch to reduce understeer:

  • Increase bumpstop range at the front so it engages later

  • Works well with stiffer springs for aero stability, while avoiding early bumpstop contact that can cause oscillation and bounce‑back
    
    

• Rear pitch control under acceleration:

  • In rear‑heavy cars (e.g., Porsche), bumpstops can limit squat and oscillation under power

  • Prevents excessive aero balance shift to the rear.

Rear Bumpstop Considerations

Most cars benefit from a high rear bumpstop range to avoid frequent contact under acceleration, which can cause:

• • Porpoising: Loss of traction and oversteer

  • Excessive front unloading: Understeer

Reducing rear bumpstop range can limit squat and help reduce exit understeer, but may compromise kerb absorption and traction. Typically, you want less bumpstop engagement at the rear so the suspension can absorb bumps and generate traction. However, in some cases, engaging the rear bumpstop earlier can stiffen the rear, limit squat, and prevent aero balance from shifting too far rearward.

Bumpstop Rate

• Softer rate: Smoother reaction when fully compressed, more compliant feel

• Stiffer rate: Sharper, more immediate resistance at full compression

Bumpstop Range

• Determines how far the suspension travels before the bumpstop engages

• Interacts with spring rate and ride height

General guideline:

• Stiffer springs for smooth tracks

• Softer springs for bumpy tracks (older circuits often bumpier than modern ones)

• Aim for the softest practical range before performance is negatively affected, this maximizes grip.

In Assetto Corsa Competizione

The suspension display shows three colour lines:

• Red – Physical bumpstop position (affected by bumpstop range)

• Yellow – Suspension travel movement (oscillates on track)

• Green – Maximum possible suspension travel