The racing bike proper has low dropped handlebars, very narrow tyres (20 to 25mm) and high gears (40 to 110in). It's good for maximum speed on smooth roads and nothing else! You must pedal hard or else the crouched riding position throws too much weight on your arms and you'll stall on hills.
There will not be enough space between the brakes and the tyres to fit mudguards safely and neither will there be any provision for luggage.
Some road bikes are available with a triple chainset. The fact is, British country lanes often have steeper gradients than you’ll find on an alpine pass - shorter but steeper - and the gears on a racing bike are low enough for a Tour de France rider to haul himself up an alpine pass. A triple chainset also lets ordinary mortals ride British country lanes!
The term 'road bike' is a very broad one, encompassing several other distinct styles more or less related to the racing bike. Closest relatives are the fitness bike and touring bike, particularly the fast tourer or audax bike.
At the bottom of the market you have low-cost racing bike clones that lack the lightness and efficiency to be contenders in any race, but are more nippy on tarmac than any mountain bike or hybrid. Cheap 'racers', 'ten-speeds' or 'sports bikes' were what everyone bought immediately before the mountain bike came in. Now the mountain bike is on the way out, they’re filtering back, but with 14 or 21-speeds.
If we confine ourselves to what can properly be called a racing bike, there are nevertheless a few variations. In addition to road racing bikes, there are 'track bikes' for racing 'on the track', which means one of those banked oval indoor or outdoor velodromes – not to be confused with rough tracks and mountain bikes and the like. Also, there are cyclocross bikes that can easily be confused with rough tracks and mountain bikes!
A track bike has a single fixed gear, hence no freewheel, and no means of stopping other than pushing back on the pedals since its only purpose is to go forwards at the maximum speed the rider is capable of – no hills and no wind. But you can still use a track bike on the road, provided you fit a front brake. Such a minimal bike is favoured by some cycling purists for commuting and even for touring!
Cyclo-cross bikes have lots more clearance than a road racing bike to accept medium width (28 to 37mm) knobbly tyres and the mud that goes with them, plus cantilever brakes - also for clearance - and somewhat lower gears to cope with the rolling drag of a soft surface.
Since they already have the space for touring tyres and mudguards, some cyclo-cross frames include the small but necessary fittings to do double-duty as a tourer.