The Rolls-Royce 30 hp was one of four cars to be produced as a result of an agreement of 23 December 1904 between Charles Rolls and Henry Royce.

Claude Johnson was keen that a six-cylinder model was included in the Rolls-Royce line-up as other "quality" makers, especially Napier, were adding them to their ranges.

As the lighting supplied uses oil for the side and tail and acetylene for the headlights, there is no other drain on the accumulators, which need to be recharged between outings.

A four-speed transmission carried over from the "Light" 20 hp model[4] is connected to the engine via a short shaft.

The crankshaft is carried in seven main bearings in an attempt to keep vibration to a minimum, a problem on many early six-cylinder engines, as the dynamics of the layout were still not fully understood.

After some early cars suffered broken crankshafts Royce modified the front flywheel to incorporate a harmonic damper which overcame the problem.