Back in the late sixties when the British motorcycle industry knew things were in hubris began an evolution of the globally successful Bonneville headed twin engined T series. The parent company BSA was waning and a merger with Norton Villiers was soon to be forced upon them. The wagons were circling…
..one if the remaining technical ‘wheezes’ they had was the creation of an oil filled frame or ‘Oil-in-Frame’ as they came to be known.

In ’71 Triumph introduced its new Bonneville & Trophy and BSA its Lightning and Thunderbolt. The photo shows their similarities such as the slab sided covers, and differences: notably the engine and gas tank. The Bonnie tries to keep a sense of its heritage whereas the Thunderbolt has new slim lines and the unit engine seems more in place. My ’72 should look like the farther model, but its developed into a 70’s hybrid.
Too little too late? The triples were a great bike, the twins were long in the tooth, worker political going on were afoot and the CB750 was running roughshod across the world. The death knell was run, BSA had a year and Triumph about ten of hobbling along.
However both good looking bikes…