At high speeds, air moving over the RC car can cause lift, making it harder to control. A well-designed spoiler pushes the rear of the car downward, increasing traction on the rear wheels. This helps in better cornering grip by preventing the rear end from sliding out (reducing oversteer); and improved acceleration by keeping the drive wheels (especially in RWD setups) planted on the surface.
Note that a larger or steeper spoiler increases downforce but can also create drag, reducing top speed. In contrast, a smaller or lower-angle spoiler reduces drag but might not provide enough stability in fast corners.
Also note that if your RC car is low-speed or mainly used for bashing, a spoiler might not have a noticeable effect. Also, if the car is driven on low-traction surfaces like loose dirt, adding a spoiler won’t help much because the tires won’t have enough grip to benefit from the downforce.
