cross bar at end of carriage pole
輗 refers to a specific part of a traditional carriage: the crossbar at the end of the pole that connects the vehicle to the yoke or harness.
輗 combines 車 (vehicle) with 兒, which likely contributes the sound. The character specifically names a crossbar at the end of a carriage pole.
The left side is 車 (vehicle), and the right side 兒 suggests a child. Imagine a child sitting on the crossbar at the end of a carriage pole, holding on tightly.
For ゲイ, picture a gate at the end of the carriage pole: the crossbar acts like a gate that connects the horse. Gate -> ゲイ.