RC (Radio Controlled) cars have become highly adjustable machines, particularly when it comes to suspension setup. For racers and enthusiasts, small suspension adjustments can have a noticeable effect on how a car accelerates, brakes, corners, and handles bumps. One of these adjustments is suspension droop.
Droop screws are used to control how far the suspension can extend downward. Although they are simple mechanical stops, changing droop can affect weight transfer, available suspension travel, stability, traction, and even the resting ride height if the screws are adjusted far enough.
In this post, we will look at what RC car droop screws do, how they work, how they affect vehicle handling, and how to adjust them correctly.
What Are RC Car Droop Screws?
Droop screws are adjustment screws normally located in the suspension arms of an RC car. Depending on the suspension design, the screw contacts the chassis or a dedicated droop pad and acts as a mechanical stop.
The primary purpose of a droop screw is to control the maximum extension, or downward travel, of the suspension. Tightening the screw generally causes the suspension arm to contact its stop sooner, reducing droop. Backing the screw out allows the suspension to extend farther, increasing droop.
This is different from suspension compression. Droop controls how far the wheel can move downward relative to the chassis when the suspension extends.
It is also important to distinguish suspension extension from shock rebound damping. A droop screw can reduce the amount of available rebound or extension travel, but it does not change how quickly the shock rebounds and it does not change the spring rate.
How Do Droop Screws Work?
As the suspension extends, the suspension arm moves downward until something limits its travel. On vehicles equipped with droop screws, the screw eventually contacts the chassis or droop pad and prevents the suspension arm from moving any farther.
Turning the droop screw farther in normally makes this contact occur sooner. This reduces the amount of suspension extension available. Turning the screw out allows the suspension arm to travel farther before reaching the stop.
For example, if the car is lifted off the ground, a suspension setup with more droop allows the wheels to hang farther below the chassis. A setup with less droop prevents the wheels from dropping as far.
Can Droop Screws Change RC Car Ride Height?
Ride height and droop are normally treated as two separate suspension adjustments. Ride height is generally adjusted using the shock spring collars, spring preload, or another ride-height adjustment provided by the manufacturer. Droop is used to control maximum suspension extension.
However, a droop screw can affect the car’s resting ride height if it is tightened far enough. If the droop screw reaches the chassis before the suspension reaches the position it would naturally settle at under the weight of the car, the droop stop begins limiting the resting suspension position. This can physically hold the chassis lower.
Therefore, it is possible to lower an RC car using the droop screws, as demonstrated in the video above. The important tradeoff is that lowering the car this way also reduces the amount of suspension extension available from that resting position.
In other words, using droop screws to lower the car also sacrifices some rebound or downward suspension travel. For most racing setups, ride height and droop should therefore be adjusted independently unless there is a specific reason to use the droop stop to influence the resting position of the suspension.
Effects of Reducing Droop
Reducing droop means restricting how far the suspension can extend. This is often useful on smooth racing surfaces where large amounts of suspension travel are unnecessary.
Less droop can reduce the amount the chassis is allowed to pitch during acceleration and braking and can make the car feel more responsive and stable. During cornering, the inside suspension normally extends as the chassis rolls toward the outside tires. If the inside suspension reaches its droop stop, further extension on that side is restricted. This can limit additional chassis roll motion once the droop stop becomes active.
It is important to understand that tightening a droop screw does not make the spring itself stiffer. The spring rate has not changed. Instead, the available suspension travel has been reduced.
Advantages: Reduced suspension extension, potentially less chassis movement, increased stability on smooth surfaces, and the ability to limit excessive weight transfer. If adjusted aggressively, the droop screws can also lower the resting chassis position.
Disadvantages: Less suspension travel is available to keep the tires in contact with uneven terrain. Excessively reducing droop can cause a tire to unload or lift sooner and may reduce grip on rough or bumpy surfaces.
Effects of Increasing Droop
Backing the droop screws out allows the suspension to extend farther. This provides more downward wheel travel and allows the tires to follow changes in the surface while the chassis moves above them.
More droop can be particularly useful on rough tracks, off-road vehicles, and rock crawlers because the suspension has a greater range through which it can maintain tire contact with the terrain. It can also allow greater chassis pitch and weight transfer during acceleration and braking.
Increasing droop does not automatically reduce spring preload. Spring preload is normally adjusted independently using the shock’s spring collar or preload spacers. Droop simply determines how far the suspension is permitted to extend.
Advantages: More suspension extension, improved ability to follow uneven terrain, and potentially better traction over bumps, dips, and rough surfaces.
Disadvantages: More chassis movement and weight transfer may occur, and the vehicle may feel less stable or less responsive on a very smooth, high-grip racing surface.
How Does Droop Affect Body Roll?
Droop can influence body roll, but it should not be confused with changing spring stiffness or anti-roll bar stiffness.
When an RC car corners, the outside suspension compresses while the inside suspension tends to extend. With plenty of droop, the inside wheel is allowed to move downward as the chassis rolls. If droop is reduced, the inside suspension reaches its extension limit sooner.
Once the droop stop is reached, that side of the suspension can no longer extend farther. This can limit additional chassis roll motion and change how weight is transferred across the car. However, springs, anti-roll bars, suspension geometry, track width, center of gravity, and ride height remain the primary factors controlling overall roll behavior.
How to Adjust RC Car Droop Screws
The exact method for measuring droop varies between RC vehicles. Some manufacturers specify shock length, while others use dedicated droop blocks and gauges to measure suspension or axle position relative to the chassis. Always check the setup procedure recommended for your particular vehicle.
A dedicated droop gauge provides the best repeatability, although a ruler can also be useful for understanding and comparing suspension travel.
A general procedure for adjusting droop is:
- Prepare the vehicle: Place the car on a flat setup surface and make sure the shocks, suspension arms, wheels, and tires are installed as required by the measurement method recommended for your vehicle.
- Allow the suspension to fully extend: Lift or support the chassis so the wheels and suspension can move downward until the suspension reaches the droop stops.
- Measure the droop: Measure the suspension position using a droop gauge, shock-length measurement, axle-position measurement, or another repeatable reference. Compare the left and right sides and ensure they are equal.
- Adjust the droop screws: Turning the screws farther in will generally reduce droop, while turning them out will generally increase droop. Make small adjustments and keep the left and right sides equal.
- Re-measure: Lift the vehicle again and confirm the amount of suspension extension. Continue making small adjustments until the desired droop setting has been achieved.
- Check ride height: Return the car to the ground, compress the suspension a few times, and allow it to settle naturally. Measure the ride height again. If an aggressive droop adjustment has changed the resting ride height, decide whether this was intentional. Otherwise, correct the ride height using the vehicle’s normal ride-height adjustment and recheck the suspension setup.
Droop adjustments should normally be made in small increments. Even a small change can affect how quickly weight transfers around the chassis and how much suspension travel is available over bumps.
Droop vs Ride Height: The Important Difference
The easiest way to remember the difference is that ride height describes where the chassis sits when the vehicle is resting on its suspension, while droop describes how much farther the suspension is allowed to extend downward.
The two settings can interact, particularly if the droop screws are tightened far enough to become active at the vehicle’s resting position. In that situation, tightening the droop screws can lower the chassis, but it does so by removing some of the available suspension extension travel.
This is why droop is such a useful suspension tuning adjustment. It does much more than simply determine how far the wheels hang when the car is lifted. It changes the range through which the suspension is allowed to operate and can therefore influence traction, weight transfer, chassis movement, cornering behavior, acceleration, braking, and bump handling.