Road bikes, in the broadest sense, share several traits that unite their different subsections and separate them from mountain bikes and hybridbikes. Speed, lightweight frames, and efficiency are the three traits that define this category of bikes.
Speed
While fast is a relative term, road bikes take top honours when compared to any other style of bike. The large-diameter wheels with narrow tyres are the biggest contributor to a road bike’s swiftness. Wheels and tyres are light, aerodynamic, and smooth, designed to roll you down the road with as little drag as possible. Mountain bikes with their heavy, lugged tyres and mixed-surface design can’t keep up. Same with hybridsor comfort bikes, whose wheels and tyres are built with more bump absorption or durability in mind. It is the difference between going for a run in lightweight running shoes vs. hiking boots.
Lightweight
Put simply, road bikes can be made very light, because they are designed for performance only on hard, smooth surfaces. It does not matter whether it is concrete or asphalt—a road bike is not built to jump over logs, ride down rocky paths, or through sand and gravel. Other bikes have to have greater durability built into them in order not to leave a rider stranded on a mountain trail with a broken bike. Road bikes, however, see such consistently smooth roadways that they can be trimmed down to the barest minimum weight.
Efficiency
Combining fast wheels and lightweight construction with a purposeful, athletic, forward-leaning position creates a very efficient package. The wheels generate little drag. The light frame and components don’t weigh a rider down. A rider leans into the wind, rather than sitting upright like a sail and has multiple hand positions to stay comfortable for a long time.
Fast, light, and efficient are all traits of modern road bikes, though all bike designs are not the same.