two wheels; both wheels
Refers to the two wheels of a vehicle, or metaphorically to two essential elements that work together like the wheels of a cart.
自転車の両輪がパンクしてしまった。
Both wheels of the bicycle got a flat tire.
経済と環境は発展の両輪だ。
The economy and the environment are the two wheels of development.
The university develops by treating research and education as its two supporting wheels.
Quality and price have become the two wheels driving sales.