Ariel Leader Four Prototype





Make Model

Ariel Leader 4 Prototype


Production Never reached full production


Four stroke, four horisontal cylinders on the left with in-line crankshaft, OHV


696 cc / 42.5 cu in
Cooling System Air cooled
Lubrication Wet sump
Exhaust 4-into-1


Single Zenith carburetor


Starting Electric

Max Power

18.6 kW / 25 hp
Clutch Morris Minor car clutch, syncro-mesh gearbox


Final Drive Shaft
Frame Pressed steel frame with leg shields
Wheels Steel, laced wire spokes
Front Rim 3.25 x 17
Rear Rim 4.00 x 16
Front Brakes Drum
Rear Brakes Drum
Wheelbase 1448 mm / 57 in
Source National Motorcycle Museum, UK

This fascinating 700cc prototype, tested at Ariel circa 1960, shows that BMW’s four-cylinder K100 was not exactly original when unveiled in 1983.

The prophetic Ariel looks similar to the company’s innovative 250cc Leader two-stroke launched in 1958, with a pressed-steel frame, leg shields and windscreen. But the power unit is unlike anything else from a British factory. The crankshaft is set in-line with the frame and slightly offset to the right, with four horizontal cylinders on the left. Final drive is by shaft, via a four-speed gearbox is built in unit with the engine. Cooling of the exhaust port area is fan-assisted and oil is carried in a wet sump.

Found to be comfortable, tractable and extremely quiet, the luxury electric-start Leader 4 was not fast. In prototype form, the single carburetor engine designed by industry veteran Val Page produced no more than 25bhp. Ariel engineers believed their design had potential, but the parent BSA Group saw no future for it in the age of the BMC Mini car and cancelled the project.