Manillar vs. manubrio
The Spanish words manillar and manubrio both translate to "handlebar" in English, but they differ significantly in regional usage and scope. Manillar is the standard term in Spain, while manubrio is predominant in Latin America and can also refer to handles or cranks on machinery.
Manillar
B1This term is used primarily in Spain. It refers specifically to the bar used for steering bicycles and motorcycles.
Debes sujetar el manillar con fuerza cuando vas rápido.
(You must hold the handlebar tightly when going fast.)
Quiero cambiar el manillar de mi bicicleta de montaña.
(I want to change the handlebar on my mountain bike.)
El manillar de la moto está un poco torcido.
(The motorcycle handlebar is a little crooked.)
Compré cintas nuevas para envolver el manillar.
(I bought new tape to wrap the handlebar.)
Manubrio
B1This word is used throughout Latin America for bicycle and motorcycle handlebars. Unlike manillar, it can also refer to the handles of a wheelbarrow or a crank used to manually operate a machine.
No sueltes el manubrio mientras pedaleas.
(Do not let go of the handlebar while pedaling.)
El niño decoró el manubrio de su triciclo.
(The boy decorated the handlebar of his tricycle.)
El albañil agarró la carretilla por el manubrio.
(The construction worker grabbed the wheelbarrow by the handle.)
Tienes que girar el manubrio para bajar la ventanilla del coche antiguo.
(You have to turn the crank to roll down the window of the old car.)
Summary
The main difference is geographical: use manillar in Spain and manubrio in Latin America when talking about vehicles like bikes or motorcycles. However, manubrio is more versatile and can also describe levers, cranks, or handles on tools and machinery, whereas manillar is strictly for steering bars.