Wheel rise, eventually, to classical Greece after the breaking of Minoan dominance and consolidations led by pre-classical Sparta and Athens. Celtic chariots introduced an iron rim around the wheel in the 1st millennium BCE. The spoked wheel was in continued use without major modification until the 1870s, when wire-spoked wheels and pneumatic tires were invented. The wire spokes are under tension, not compression, making it possible for the wheel to be both stiff and light. Early radially-spoked wire wheels gave rise to tangentially-spoked wire wheels, which were widely used on cars into the late 20th century. Cast alloy wheels are now
Flip-flop hub Flip-flop hub Flip-flop hubs, also called double-sided hubs, are rear bicycle hubs that are threaded to accept fixed cogs and/or freewheels on both sides. There are several different types of flip flop hubs available for different applications. Their main purpose is to allow changing between two different size gear ratios on one rear wheel without the added complications of a derailleur or internal hub gear, or between a fixed and freewheeling option. By removing the rear wheel and flipping it around, the rider can switch between the two options. They are traditionally found on track bicycles, but can also be