Pulleys: Finding right size for timing
When choosing which timing pulleys and timing belts to buy, there are a few things one must consider. For example, there is the pitch of the timing pulley. The pitch is the distance from the center of one groove to the center of another. This pitch size must match up to that of the belt.
Another component is the shape of the teeth and the grooves in the belt. There are many options for this, such as trapezoidal or round. Trapezoidal may be better for higher load, while the rounder groove has lower noise and wear characteristics.
Once the pitches and the teeth are set, the diameter of the bore needs to be the same as the shaft that is going to need to fit in to that pulley. For example, the mini shaft of the motor and the shaft that will attach to the wheel.