In 1952 Rumi began preparing a motorcycle suitable for the extremely demanding off-road races. They used the Hunchback's frame, which was considerably more robust than the standard chassis, with a variety of modifications which included readily removable wheels to facilitate tyre changes, telescopic front forks, and lower gear ratios.
The machines were reserved for factory riders, and good results were achieeved in national and international competition. With production of a new engine in the spring of 1953, an updated model was launched and remained in contention until 1955, when the Sei Giorni version arrived. This Rumi was one of the first motorcycles designed and built specifically for enduro work. The Sei Giorni remained in the catalog for five consecutive years, and almost all of them went to factory riders. It did not achieve sales success as other manufacturers had moved to four-stroke engines which were favoured by by majority of competitors.