A third version of the 3½ h.p.
model was available along with the 'Standard' and 'Semi-Sporting' models
which were little-changed from their 1920 versions. The new 'Sporting Solo
T.T. Model' reflected Thomas Corbett de la Hay's
Senior T.T. win the previous year.
The Marston patented, leaf spring suspension was introduced for the
front forks of the 8 h.p. v-twin model to become standard for the range
except for the T.T. model which had Marston-made Druid style front forks.
The T.T. model had 'vee' rim brakes with a Ferodo-lined shoe at front and
back, whilst other models retained a bicycle style stirrup brake at the
front and drum brake at the rear.
Engine and Gearbox
A high compression engine remained available for the Semi-Sporting model,
and a higher compression, finely tuned sports engine for the T.T. model.
The T.T. model also had a smaller and lighter
three-speed gearbox with 'crash' sliding pinions rather than the constant
mesh 'rack and pinion' earlier gearbox. The 'crash' gearbox was to become
the standard Sunbeam gearbox.
* John Marston Ltd., 1921 'The Sunbeam Motor Cycle' Catalogue.
* Robert Cordon Champ, 1980, 'The Sunbeam Motorcycle'. Haynes Publishing.