With tubing getting thinner to reduce weight, frame strength became an issue. By the end of the 1880s, duplex tubing came into vogue. Also known as an ‘open frame’ or ‘open bottom bracket’ or ‘double diamond’, this style was copied from tricycles. With similar concerns around 1900, ‘truss’ and ‘girder’ frames had an extra tube for added strength. This was necessary if a frame was tall, but it was also sometimes used as a gimmick. The Premier ‘Truss’ had an extra tube from seat to steering head.
The extra tube the Royal Enfield ‘Girder’ ran from the bottom of the steering head to the bottom bracket.
The Elswick ‘Truss’ had two crossed down tubes.
Cycle makers worked hard to give their top-of-the-range model some sort of extra design flourish to make it stand out from the crowd and many odd frame styles appeared over the years…