The 1921 Humber 4.5 hp motorcycle was the first produced after the Great War. It had an oversquare 600cc engine and 3 speed gearbox.
A Motor Sport magazine report on the 1924 Motor Cycle Show reads, in part,
"A Humber motor cycle of vintage 1902 is shown on the special stand devoted to historical machines, and it is worth inspection prior to seeing those of 1925, in order that due appreciation of the immense strides which have been taken in the interim may be acquired. For 1925 two models are listed, the "Six days" and the Model de Luxe. It is of interest to compare the differences between the two. On the six days' model lubrication is by hand pump. A hand pump is also present on the other, but it is there for emergency use only, a mechanical pump being provided to take care of the lubrication under ordinary running conditions. The de Luxe has a B. and B. carburetter, the other has an Amac. The de Luxe model has larger tyres, and better weather protection than the other. Substantial reductions in price have been made, as is exemplified in the 'Six-days' which, formerly £55, is now only £47 10s."
... another bicycle duly came along, in the form of a 350-c.c. o.h.v. Humber. Such factors as car-style mudguards, a sensible lifting handle and substantial build and excellent finish were apparent at first sight. The gearbox gave ratios of 5.65, 7.75 and 11.59 to 1, and in spite of a weight of 260 lb. the Humber steered exceedingly well and cornered really fast.
The 75 by 79 mm. engine used an M.L. magneto and a B. and B. carburetter, and equipment included knee-grips and a comfortable saddle; the price was £60. The Bonniksen speedometer showed 68 m.p.h. as the best registered, but it was felt that 75 m.p.h. should be possible under good conditions; 40-45 m.p.h. could be kept up with no sign of overheating and the only criticism was a vibration at 35 m.p.h., the only trouble in a week's riding a broken outer inlet-valve spring. Both brakes were smooth and powerful. The easy gear-change was a most notable feature; incidentally, the throttle lever opened inwards.