Bicycles of dizzying speed, weighing tons – and decadently expensive: World Bicycle Day is coming up on June 3, so here’s a look at not only the variety of bikes, but also the extremes – and entries in the record books: With outside help and a slipstream: 296 km/h According to the Guinness Book of Records, the fastest ride on a bicycle ever was by Denise Mueller-Korenek, who achieved a speed of 296 km/h on her custom-built bicycle in September 2018. She did so not on her own power, but towed by a car in the salt flats of the US state of Utah and then, after the tow rope was disengaged. The mot…