Suspension

The suspension is the system of tires, springs, shock absorbers, rods and linkages that connects the car to its wheels and allows the wheels to move up and down independently of the chassis or body. Suspension systems must support both road holding/handling and ride quality, which are at odds with each other.

It is important for the suspension to keep the road wheel in contact with the road surface as much as possible, because all the road or ground forces acting on the vehicle do so through the contact patches of the tires.

The suspension prevents the car from rolling and provides damping which protects the vehicle itself and its components from damage and wear. The design of front and rear suspensions of an RC car are often different.

The tuning of the suspension system involves finding the right compromises for optimal performance.

Overview of the suspension system

The are litteraly dozens of components in an RC car suspension system, the most obvious and the largest being the schocks. The entire system however relies on smaller parts all of which play an important role in the handling of the car.

Overview of the main components

When it comes to the suspension system, a common beginner error with RC cars is the overwhelming focus on shocks. In reality, a chain being only as strong as its weakest link, the best schocks will not correct the handling of a car fitted with the wrong wheels and tires or a car with an improper camber setting.

The understanding of the role of each part in the quality of the suspension is paramount to the proper optimization of an RC car chassis.

• Wheel: The wheels of an RC car hold the tires in place and affects handling and suspension. Depending on their size, weight, proper balance and flexibility, the wrong wheels can dramatically impact the handling of a car. For more information, read the Wheels dedicated page.
  
  
• Tire: The tires are the point of contact of the RC car with the ground. Their size, weight, density, toughness or softness of the rubber as well as the tires tread all have a major influence on how a car behaves. For more information, read the Tires dedicated page.
  
  
• Stub axle: The Stub axles are short axles that carry the front steered wheels and are capable of limited angular movement. The wheels are attached on the stub axles using a wheel nut. For more information, read the Stub axle dedicated page.
  
  
• Wheel nut: Also called a lug nut, it is a fastener used to secure the wheel on the vehicle. Some RC cars do not use wheel nuts to secure the wheels in order to allow for fast replacement of the wheels specifically during competitions. For more information, read the Wheel nut dedicated page.
  
  
• Suspension arm: A core components of the suspension system, they are a direct connection points between the front wheel assemblies and the vehicle's frame. They offer a limited range of vertical movement guiding the wheels up and down with the road surface. For more information, read the Suspension arm dedicated page.
  
  
• Turnbuckle: A link with screw threads at both ends that can be turned to bring the ends closer together and that is used for tightening a rod or stay. The rod itself connects two parts of an RC car and the main ones present on an RC car are used to adjust camber, toe and steering. For more information, read the Turnbuckle dedicated page.
  
  
• Shocks: Also called dampers, the shocks dampen the movements of the spring thus affecting handling conditions during cornering while smoothing out irregularities on the road. Most modern RC shocks are adjustable and their proper setting will improve the quality of the ride and the performance of the car. For more information, read the Shocks dedicated page.
  
  
• Shock tower: A rigid part that mounts on the chassis and holds the mount of the top part of the shocks. It has several holds allowing to change the position of the shock on the tower adjusting its angle and height. For more information, read the Shock tower dedicated page.
  
  
• Steering knuckle: A rigid part that connects the wheels and the steering assembly on the car, turning the wheel when the servo generates a motion of the steering assembly. Contrary to a steering turnbuckle, it is not adjustable. For more information, read the Steering knuckle dedicated page.
  
  
• Caster block: A rigid part that allows for the adjustment of the range of vertical movement of the suspension arm in order to modify caster which is the difference between the angle of the steering block pin and the verticalwhen viewed from the side of the car. For more information, read the Caster block and the Caster dedicated pages.
  
  
• Hinge pin brace: A rigid part which holds the suspension arms in place and prevents bending or suspension arm damage. For more information, read the Hinge pin brace dedicated page.
  
  
• Sway bar (or anti-roll bar): Flexible parts mounted on the front and rear of the chassis and used to reduce chassis roll while cornering by connecting the left suspension arm of the car to the right one. Typically used on high-traction surfaces to keep the chassis flat through the turns. They also help providing even traction on all tires resulting in a more responsive car. For more information, read the anti-roll bar dedicated page.

RC suspension operations and tuning

The main purpose of the suspension system is to stabilize the ride height to provide optimal traction and speed while protecting the car and its components. By making adjustments to the suspension system, it is possible to greatly improve the car's cornering ability, traction and optimize the ride for different types of terrain.

Adjustments to the suspension system can be made in many ways:

• Camber and toe to control how the tires contact the driving surface
• Droop to limit the suspension arms vertical traveling range
• Position and angle of the shocks
• Spring hardness, spring tension and shock oil viscosity

Adjusting droop

Droop is the amount of down travel of a suspension arm. It can be set independently from front to rear but should be similar from side to side. Droop can allow or limit the weight transfer from one side to the other, thus altering handling and control of an RC car.

Droop is directly linked to a particular car model, type of track surface type or driving style. Droop is extremely helpful with handling weight transfer from front to rear in order to maximize traction and steering.

Setting up droop

Position of the droop screw on a suspension arm

The first part of the procedure to setup droop is to put the car down on a flat surface and let the suspension settle down. It is then possible to measure the droop value as the distance traveled by the suspension from the settling down position (ride height) to the moment the tires leave the ground when lifting the chassis up. Droop value is then equivalent to:

Height after life up - Ride height = Droop value

The droop value can be increased or decreased by turning the droop screw present on most modern RC cars.

Adding droop on one end of an RC car will generally increase grip on the other end. Running a lot of rear droop, allows more weight to transfer to the front wheels during braking, which may or may not be desirable depending on driving styles or surface conditions.

Since the Droop value depends on the ride height, changes to the suspension or wheels might impact the droop value.

Suspension tuning

The suspension is a complex mechanical system where many moving parts work together to operate. Whatever its configuration, it relies on the wheels to perform in an optimal manner. All upgrades, adjustments and enhancement of the suspension system should begin by using the appropriate quality wheels and tires adapted to the terrain the car will perform on.

Below are common knowledge rules important to RC suspension tuning:

• The right tires for the right terrain: making sure to fit the car with the appropriate wheels and tires prior to making adjustment to the suspension system
• Make incremental changes: a small change to the suspension system may have great impact on the car's behavior. Making small changes and testing will improve the chances of finding the optimal configuration.
• Testing is paramount: each change to the suspension configuration should be confronted with a driving session.
• Cornering well is better than speed: adjusting suspension with focus on on the car's cornering ability is more efficient in term of performance than sheer speed since going out of a track costs more time than driving slow.

Adjusting Camber

In an RC car, the term "Camber" refers to the angle of a wheel relative to the driving surface. When a tire that is perpendicular to the ground, it is said to have zero camber, when it is leaning toward the chassis, it is said to have negative camber and when it is leaning away from the chassis, it is said to have positive camber.

The Camber angle can be modified by rotating the camber turnbuckle (camber link) thus altering its length and tilting the wheel. Most models are set with 1° or 2° of negative camber on all four wheels while positive camber is virtually never used.

For detailed information on Camber and Camber tuning, read the Camber dedicated article.

Adjusting toe

The term 'toe' refers to the angle of the front (or rear) tires when viewed from above. If the front of the tires angles in (or towards the chassis), that is 'Toe In'. If the front of the tires angles out (or away from the chassis), that is 'Toe Out'.

Toe can be adjusted by rotating the steering turnbuckle thus altering its length and tilting the wheel. Changing the toe will have a direct impact on the car's behavior:

More front toe-in More on-power steering	More front toe-out More off-power steering More initial turn-in Smoother on-power
Less rear toe-in Less forward traction More high-speed stability More rotation in turns	More rear toe-in More forward traction Less high-speed stability Less rotation in turns Generally suitable for low-grip tracks

For detailed information on Toe and Toe tuning, read the Toe dedicated article.

Differences between front and rear suspensions

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Differences between 2WD and 4WD suspension systems

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