A Tribsa, [1] was a custom built café racer or off road motorcycle of the 1960s and 1970s. A Tribsa comprises a Triumph parallel twin engine installed in BSA motorcycle frame. The purpose was to combine the best elements of each marque to give a superior bike to either.
The Tribsa name is a portmanteau word, an amalgamation of Triumph and BSA.[2][3]
Although both the BSA A65 and the Triumph 650 cc twins engines were pushrod overhead valve (OHV) units, only the Triumph had twin camshafts, which supposedly facilitated tuning for a greater power output. The BSA frame was a duplex-cradle design which was considered stiffer and stronger than the Triumph's single downtube item.
A batch of nine TriBSAs were planned by the BSA-Triumph for the 1966 ISDT using 348 cc, 490 cc and 'special capacity' 504 cc 'short' Triumph twin engines in a frame using geometry from the BSA Victor scrambler, Victor front forks and wheel together with a Triumph QD rear wheel in a Triumph swinging arm[4] A light-alloy Gold Star type fuel tank and a steel oil tank were fitted together with three ignition coils, one as a spare.[5][6] The 490 cc prototype was finished and tested in Wales with the remaining batch utilising the other engine sizes scheduled to follow.[6] Some bikes were intended to be named Triumph and the others BSA, to enable two opportunities for makers' honours.[7][8][9]
A Tribsa was built experimentally at Meriden by Triumph in 1973 using surplus BSA A65 frames.[10] This led to a 'factory Tribsa' which was to use the BSA A65 frames with the 650 cc TR6 engine.[citation needed] Not many of these hybrids were produced and factory records are vague.
In today's vintage off-road events, Tribsas may be seen competing in motocross, enduro, and trials.[11][12][13]
A popular alternative to the Tribsa was the Triton which combined a Triumph engine in a Norton Featherbed frame, a chassis which had yielded victories in the Isle of Man TT for Norton.