Originally Posted by
Daniel4
In Newton's pendulum, the kinetic energy of the first ball is transmitted through all the balls to the last because they are perfectly elastic and very hard. If the balls were perfectly inelastic, the last ball would not move at all because all of the balls would have absorbed all the energy.
In a hard tire, all the energy is transmitted through and you can feel all the vertical bumps. Not only do you go up and down, you go forward.
In a soft tire, the rubber absorbs all the energy and reduces your forward motion. Try riding on grass and sand where the soft ground is absorbing all the energy. Then compare that with riding on concrete, asphalt or on a perfectly smooth and hard track of a velodrome. The hard surface transmits all your energy.
The rougher the road surface, the more you don't want the vertical force inputs from the road transmitted and absorbed directly by your body. On a paved road that basically translates to vibration and the occasional more abrupt hit from potholes etc. All of which adds to your accumulated fatigue and ultimately slows you down. If the road is super smooth then you can run higher pressures and reduce the hysteresis losses in compressing the tyre. But as the road surface becomes less smooth, it soon becomes more beneficial overall to absorb the road inputs within the tyre rather than through your body. You only have to compare velodrome track tyres with mountain bike tyres to see the two extremes at play. Both are fastest in their element.
Where people get confused is attributing speed with a harder ride. Beyond a certain point it becomes counter-intuitive.