The maximum speed at which a person can ride a bike depends on several factors, including the rider's physical abilities, the type of bicycle, the terrain, and external conditions.
For an average cyclist on a typical road bike, reaching speeds above 30 km/h (18.6 mph) requires a decent level of fitness and pedaling efficiency. However, many experienced cyclists can easily reach and sustain speeds well beyond 30 km/h. Professional cyclists, for example, can reach speeds exceeding 40 km/h (24.9 mph) or even higher during races.
Various factors can affect a cyclist's speed, such as wind resistance, gradient of the road, riding position, fitness level, gear ratio, and road conditions. Cycling at higher speeds also requires more physical effort and skill in bike handling to maintain stability and control.
It's worth noting that different types of bicycles, such as time trial bikes or electric-assisted bikes, can achieve higher speeds due to specific design features or added assistance. Moreover, factors like drafting (riding closely behind another cyclist to reduce wind resistance) can also contribute to increased speeds.
In summary, while 30 km/h can be a respectable speed for an average cyclist, it's certainly not an absolute limit, and many factors come into play when determining how fast a person can ride a bike.