The Rolls-Royce 20/25 built between 1929 and 1936 succeeded the 20hp as Rolls-Royce's "small car". It was intended to appeal to owner drivers but many were sold to customers with chauffeurs.
The in-line 6 cylinder overhead valve engine was similar to that used in the 20HP but was enlarged to 3699 cc by increasing the bore from 76 mm to 82 mm with the stroke remaining at 114 mm. A single Rolls-Royce carburettor was used and both coil and magneto ignition were fitted. The four speed gearbox was mounted in unit with the engine and a traditional right hand change used. Synchromesh was fitted to third and top gears from 1932.
The substantial chassis had rigid front and rear axles suspended by half elliptic springs with braking on all four wheels assisted by a mechanical servo. Separate rear brakes were fitted for the handbrake. The famous Rolls-Royce radiator with triangular top was used with vertical louvres, the angle of which could be adjusted to control engine cooling. To begin with, the radiator shutters were operated manually via a lever on the dash; later cars were fitted with automatic control via a thermostat.
Source: Wikipedia, 2011