The present disclosure relates to a wheel built-in power system for an electric golf bag trolley, including a motor, and a worm wheel engaged with an output worm of the motor, a spindle of the worm wheel being connected to a hub of any wheel of the electric golf bag trolley. The wheel built-in power system for an electric golf bag trolley of present disclosure is small in size and light in weight, and can be installed in wheels of an electric golf bag trolley, thereby effectively reducing the size of the electric golf bag trolley after being folded, facilitating movement and storage.

An air disc brake for a road vehicle is proposed, having a mechanism for causing retraction of the brake pads when the brakes are no longer applied, to avoid parasitic drag caused by continued contact of the brake pads against the brake disc. The proposed mechanism includes a pin located in a fixed position relative to one brake pad, and extending through an aperture in the other brake pad. A coil spring is supported on the pin, and pushes the brake pads apart. Where the pin extends through the aperture the extent of the pin provides an indication of the wear state of the pads and disc, which is visible through apertures in the wheel rim.