🛞 Tire Insert
A foam ring fitted inside a tire before gluing, supporting the sidewall so it doesn't collapse or roll off the wheel under hard cornering.
What it actually does
The insert is the foam ring inside a rubber RC tyre. It is doing most of the work you would expect from air pressure in a full-size tyre: supporting the sidewall, controlling how the tread deforms under load, and stopping the tyre folding over in corners.
In practice
Firmer inserts hold the tyre's shape, giving more precise steering and better support on high grip. Softer inserts let the tyre conform to rough ground and generally find more traction on loose surfaces. Changing inserts alone can transform how a car feels without touching a single setup screw.
Worth knowing
Inserts collapse and take a set over time, especially after hot runs. A car whose handling has slowly gone off with no setup change is often just running tired inserts.