exterior rim of wheel
輞 refers specifically to the outer rim or felly of a wheel, the circular part that holds the spokes and tire.
輞 combines 車 (vehicle, wheel) with 罔, which likely contributes the sound and may relate to a net-like or encircling structure, fitting the wheel rim.
The left side 車 is a vehicle, and the right side 罔 looks like a net stretched around a frame. Picture the outer rim of a wheel as a circular net holding everything together.
For ボウ, imagine a bow-shaped wheel rim: bow -> ボウ, and the curved rim of the wheel bends like a bow.