crossmember: parts of the truck

Can anyone tell me what part of the truck is the "crossmember"? I've search everywhere, believe me. It is a kind of bar (like the bumper) that crosses all the vehicle, cast in iron...I don't (and my mechanic) doesn't know.
Besides, can any one tell me the differencia between "rim and tyre"? ¿Cubierta y llanta?
For the guy who is translating the truck manual....have you translated "Banjo"? and spindle? (the first is "cañonera" and the second "manguete"- for argentinians)
thks to all:o

Crossmember = travesaño
Rim = rin
Tire = llanta

Coincido en que puede ser travesaño, encontre igual miembro transversal, pero a lo mejor te quede igual "barra del chasis".

Rim es el "Rin", osea la parte metalica, el aro donde va montanda la Llanta "Tire "(cubierta-caucho, etc)

espero te sirvan mis comentarios