Adjust Weight Distribution
It’s a balancing act
When tuning an off-road vehicle, it is easy to get zoned in on the shocks, springs, and differentials to change the handling of the car or truck. However, the total weight of the vehicle, as well as the weight distribution, can have a profound effect on handling and flight characteristics, and should be a tuning tool for all drivers. This guide will explain the effects of weight distribution and how to change it for better handling and jumping.
Total Weight
The total weight of the vehicle has a direct effect on its ability to accelerate and corner effectively. The heavier a vehicle is, the slower it will accelerate. The motor has to work harder in a heavier vehicle, and it takes longer to get the mass moving. Heavier cars and trucks will also drain batteries or fuel tanks faster due to the added strain on the motor or engine. In addition, heavier models will corner less effectively because they will have more chassis roll. The added chassis roll causes extra camber change, which lowers the cornering potential of the vehicle.
For most conditions, the car or truck should be run as light as possible for maximum acceleration and cornering potential. Getting the weight down is not too hard for most models. Many shortcourse trucks have extra nerf bars and bumpers that can be removed without detriment. Proper maintenance can also help keep weight down. The vehicle will naturally get heavier as dirt gets stuck in the chassis, especially on a damp or freshly watered surface, so regular cleaning will help.
In low-grip conditions, a heavier car or truck may perform better. In this scenario, the vehicle is usually lacking forward bite and thus top speeds are low. Extra weight at low speed can help the pins of the tires dig into the surface harder for better penetration. Since top speeds are down in slippery conditions, the cornering speeds are down too and the chassis roll and camber change are naturally lower, so the added weight will not hurt cornering as much as if the surface had more grip. The best place to add weight is as close to the centerline of the vehicle as possible. On a 2WD model, it is usually better for the added weight to be as far back in the chassis as possible for the best traction. On a 4WD model, putting the weight slightly forward in the chassis will help keep the load more even between the front and rear tires for the best acceleration. The amount of weight that should be added will depend on the conditions and how the vehicle responds. A good start would be to add weight in 1-oz. increments until a handling change is experienced.
Weight Distribution
The total weight of the car or truck is just one part of the story, as the way the weight is distributed between the front and rear axles affects both the handling and jumping characteristics. Weight distribution is usually expressed as a percentage of the total weight that the front axle carries. This is sometimes referred to as “nose weight.” It is possible to calculate the nose weight of the vehicle if you have a set of scales that you can put under each tire. The nose weight is then the weight of the front two tires divided by the total weight of the vehicle. The range is usually between 45% and 55%, but it is less important to know the actual value than it is to know how the handling will change if weight is moved forward or backward in the chassis.
The more nose weight that a vehicle has, the tighter it will be during cornering and vice versa. Weight farther forward in the truck will cause more weight transfer across the front axle than the rear, which will cause the front tires to lose grip first, making the vehicle tight. This is especially true in high-speed corners where the vehicle is experiencing higher centrifugal force. The most common way to change the weight distribution is to move the battery fore or aft in the battery tray. In some nitro and 4WD models, this is not possible, but the distribution can be changed by adding weights to the front or rear of the car or truck.
Weight distribution also affects acceleration. For maximum forward bite, the driven tires should carry the most weight. In a 2WD model, this means that most of the weight should be shifted to the rear, and this is why many 2WD off-road vehicles are designed with the motor behind the rear axle. In a 4WD model, however, all four tires help accelerate the vehicle, so it is advantageous to have a slightly forward weight bias. Under acceleration, weight transfers to the rear of the vehicle, so a little bit of forward bias will help keep the wheel loads even, front to rear, so that all four tires will have the same load.
When making changes to the front-to-rear weight bias, it is important to keep the jumping performance in mind. Moving weight to the rear may help get more forward bite, but it will also make the car or truck more prone to taking a nose-up attitude in the air. You can compensate by modulating the brake and throttle to keep the vehicle level in the air, but the less intervention your setup requires, the better.