Whilst working in his office at Stevenage in 1936, designer Phil Irving noticed two drawings of the Vincent HRD engine laying on top of each other in a "V" formation.

[2]: 93, 94  This first Vincent V-twin engine was installed in a frame originally built for a record attempt by Eric Fernihough, who no longer required it.

Comprising a rear frame member (RFM) of two upright triangular arms pivoting at the bottom of the frame and attached to two spring boxes and damper at the top, this system had been used on all Vincents from the first Vincent Special prototype built in 1927.

With a 6.8:1 compression ratio, the Series A engine produced 45 hp (34 kW) @ 5500 rpm, and was capable of 110 mph (177.0 km/h).

As was the case with the Vincent singles, the transmission in the Series A was a separate 4-speed unit supplied by Burman with a triplex chain primary drive, but with heavy-duty internals and a different wet multiplate clutch.

Bill Clarke nicknamed it `The Snarling Beast’ and a reporter struck by the mass of external pipework dubbed it `the plumber’s nightmare’.

[1]: 19, 20 Design of a radically revised Series B Rapide took place during World War II, and the bike went into production in 1946.

[1]: 124–127  The front and rear suspensions were unchanged, being a Brampton girder fork at the front and a cantilever system at the rear, although a hydraulic shock absorber and spring assembly later replaced the original twin springboxes and friction damper.

By this time Vincent believed that the Brampton fork had outlived its value, but they had resisted adopting the increasingly common telescopic forks, feeling that they were not sufficiently rigid in torsion, did not offer enough adjustment, and did not handle well when ridden hard when a sidecar was attached.

Long coil springs ran beside each blade from the fork ends to eccentric members in the bottom links.

[7]: 71 During the Korean War nickel chrome steel was officially regulated, meaning the correct materials for some components (e.g. gears) was not available.

The Series D used a modified RFM with relocated spring box lugs and a new single Armstrong spring/damper unit that increased suspension travel by 30% to a full 6 in (152 mm).

[1]: 36  The previous box-section UFM was replaced by a simple tube with brazed lugs at each end bolted to a slightly modified version of the Series C malleable steering head casting.

A change of the rear subframe brought a new seat support, which freed the passenger footpegs from the swingarm-connected-seat struts of the Series B and C models.