The A-bike is a folding bicycle invented by Sir Clive Sinclair in the United Kingdom and released on 12 July 2006. It weighs 5.5 kilograms (12 lb) and folds to 67×30×16 centimetres (26.4×11.8×6.3 in), small enough to fit in a rucksack.
The A-bike was designed by a team at Daka International Ltd, in Hong Kong, and Sinclair Research over 5 years. It was announced to the public in 2004. Clive Sinclair envisioned the A-bike, and Alex Kalogroulis was the main design engineer.
The A-bike's telescoping structure reduces its apparent volume to about 25% in its collapsed state. A twin-chain system enables the bike to travel about 3.2 metres (10.5 ft) per crank rotation despite the bicycle's small-diameter wheels (6 inches or 15 centimetres). The crankcase housing encloses almost completely the drive mechanism, protecting it and preventing oil stains on clothing or floor surfaces.
Small-diameter wheels may not be able to traverse uneven terrain, so the slightest imperfection in the intended path may interrupt progress, even on paved surfaces.
In November 2006, A-bike was featured on UK television programme The Gadget Show, alongside the Strida. The distribution company behind the A-bike was featured on the UK Television programme Badger or Bust broadcast on the 5 June 2007. In the Top Gear epic race Car vs. Train 2. Richard Hammond and James May carried A-bikes in their suitcases and unfolded them to bike from a ferry dock to a cable car. The magazine A to B described the A-bike as a "fabulous folder, but almost unrideable".