The pneumatic tire and the chain drive, followed by the development of gears, revolutionised bicycling in the later 1800s. In the last fifteen years, there has been a revolution of sorts in the development and use of new materials for building frames. It wasn't that long ago that frames were made out of cast iron or even wood. Today bicycles are made out of exotic materials such as titanium, aluminium, and carbon fibre. Bicycle frames in the 1990s are lighter and stronger than ever before.