reins
軜 centers on the straps used to guide a horse: reins. It is a specific term for the leather lines held by a rider or driver.
軜 combines 車 (vehicle, cart) with 内 (inside), likely indicating something inside or attached to a vehicle. The exact historical development is uncertain, but the character is used for reins, which are connected to a cart or carriage.
The left side 車 suggests a cart or vehicle, and the right side 内 means inside. Picture the reins as the straps that go from inside the cart to the horse, controlling the vehicle.
For ドウ, imagine a dough-like leather rein stretching as you pull it: dough -> ドウ, and the rein is made of tough, stretchy leather.