Bike frames used to be made of steel because it was the only material strong enough, but plenty has changed since the early part of the last century.
Riders want bikes that are as light as possible, but that will also stand up to the massive stresses their powerful legs develop.
A frame that is too "whippy" will see wasted effort, so all the power must go to the pedals and not the frame - so lightweight plastic could not be used.
The first developments to make steel lighter were alloys, which are still used on most normal bikes.
But many in the sporting scene have moved on to aluminium, with big oversized tubes to make them strong as well as light.
Riders also use carbon fibre - often in time trials - where these Formula One-style materials can be moulded into aerodynamic shapes which are fast in a straight line but tricky around corners.
The most modern designs - such as Chris Boardman's legendary 1992 Olympics-winning machine - have now been banned in an attempt to level the playing field.
The choice of frame material for the serious mountain climber is titanium, the lightest material in the sport but one that can be hard work to ride for long distances.
For these reasons riders will often use a steel alloy or aluminium bike for the ordinary flat stages, titanium on the mountain days and carbon fibre in the time trials.
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