There is a big difference between 20 mph, 25 mph, and 30 mph...

Some wattage figures... using my weight, road bike weight and stats, aero position... and assuming I am on flat ground with no wind for the sake of comparison.

For me to cruise at 20 mph / 33 kmh I need to sustain an output of 145 watts and can do this all day.

For me to ride at 25 mph / 40 kmh I need to maintain an output of 261 watts.

To ride at 30 mph I need to put out 432 watts.

When I climb that short 12% grade on the way to work at 20 mph I am laying down just over 1000 watts of power.

To sprint at 38 mph / 60 kmh I also need to put out nearly 900 watts.

Professional riders are amazing.