Cyclists have all experienced this: if the tire is fully inflated, the bicycle rides particularly smoothly and effortlessly; if the tire is deflated, it's much harder to pedal it. Therefore, people will check whether the tire is fully inflated before riding. So, why is it harder to ride a bicycle when the tire is underinflated?
By observing, we can find that the contact area between the deflated tire and the ground is very large. Could this be the reason for the increased "friction"? Intuitively, it seems that way, but physics tells us that generally, friction is not related to the contact area, but only to the contact material and pressure; Moreover, the wheel that provides power for the bicycle is the rear wheel, and the friction of the rear wheel is forward-directed. Therefore, the greater the friction, the easier it should be to ride.
In fact, the reason why it's difficult to ride a bicycle is not due to an increase in "force", but an increase in "torque". Due to the deflated tire, the action point of the ground support force will be separated from the action point of gravity. Gravity generates a torque around the action point of the support force, which will "resist" the power torque generated by the chain, making it naturally harder to pedal. The more deflated the tire is, the harder it will be to ride the bicycle.