[newtonsfirstlaw]

Something I've noticed in the last month is that tarmac isn't tarmac. I'm not sure whether it's my imagination, but I seem to be able to coast quite a bit better on tarmac composed of the fine particles compared to the tarmac where there is tar over gravel sized particles.

Whenever I see this smooth surface, I make sure my car is running over it if it only covers part of a lane.

If I'm correct and this is not just the placebo effect, I can see it springing from several potential sources (listed in order of estimated importance). The first is that there is more individual deformation of the tire with gravel sized bumps. That energy gets turned into heat, which is coming from your car's kinetic energy and ultimately from fuel.

The second is that vibration gets damped by shock absorbers. These shock absorbers get hot as they do their work... and that heat came from the same place too.

The last is that if you follow Matt Weaver's Virtual Edge and have read some of his writings, laminar flow can get disrupted by vibration. If you are traveling on a vibration free surface, you may be getting some more laminar flow than you used to get with a corresponding drag reduction.

Lastly, I don't think it's placebo effect. In a recent test of a bicycle commute from a place I was thinking of buying, I rode my MTB on the designated footpath style bike track and then the road (smooth style tarmac). Very noticeable difference in effort required to go a certain speed.

That's the great thing about bicycles - they are such an excellent ecodriving tutor since your own motor is so tiny and makes you feel pain if you push it too fast.