# No friction in pure rolling - how about driving a car?

I remember the un-intuitive result that pure rolling without acceleration involves no friction by the law of conservation of angular momentum. Conjectures:

1. I understand that when I'm driving a car at constant velocity on a straight, flat road, the wheels are in a state of pure rolling?
2. One reason I have to keep expending fuel is that the tire is not in point contact with the ground, causing the normal force from the ground to be off-center, providing a decelerating torque?

Another reason I have to keep expending fuel is that there is some air-resistance.

First, are my conjectures correct? Also, in driving a vehicle in the real world under the conditions previously described, is the friction force still zero, even factoring in air-drag and real world imperfections?

• I remember the un-intuitive result that pure rolling involves no friction do you mean to say rolling without slipping and without acceleration? Commented Mar 23, 2019 at 19:39
• Yes. I'm particularly interested in what happens when driving a car/bicycle on a straight, flat road at constant velocity. That is rolling without slipping, right? Commented Mar 23, 2019 at 19:41
• The car squashes the tires as they roll along. As each part of the tire expands back to its ordinary shape after being squashed, you don't get all the energy back. Commented Mar 23, 2019 at 19:46
• Besides that, you also lose energy because of wheel deformations which although elastic do not return total energy, its kind of lost and spread through the wheel. Commented Mar 23, 2019 at 19:46
• Can we classify these phenomenon as being contributions by friction? Commented Mar 23, 2019 at 19:57