Smooth Road Effect
 

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.

Sounds to me like you got it right.

I'd agree. It seems like I can glide for ages on a smooth road, but a bump road I'm almost plusing. Since borrowing my scangauge to a friend I had been counting the seconds while gliding and did notice a difference when on smooth roads versus course/bumpy ones.

Concrete pavement is the best, followed by smooth asphalt, gravel asphalt, brick/cobblestone, gravel, no pavement (grass, dirt, mud, sand, etc.). Your mileage losses on bumpy surfaces is caused by the energy lost by the movements of the suspension system.

I'm willing to bet grooved concrete doesn't fare as well (perhaps between smooth asphalt and gravel asphalt).... The noise itself is an indicator of energy losses....

on bumpy surfaces or rocky surfaces it sort of creates a bogging effect as if your tires are low on pressure, which causes you to have to push your engine more to get it going at a constant speed. Plus if it's bumpy, it's like a bunch of really small speed bumps trying to hunt you down. gravel you do bog which takes down your economy fast.

I don't like the roads that seem like a giant comb was ran through it while it was still wet. lots of noise, and tire wear, and heat generated and just not right at all, but I'm seeing a lot of new bridges with this type of concrete road. I like the black asphalt types with no noise, and any dips are really smooth and work with your suspension. Plus it makes any suspension feel like your in a Cadillac :D

I agree - but I do agree with why it's there.... Here's a list of static coefficient of friction for rubber on concrete and asphalt

rubber on dry concrete .5 to 1.2
rubber on wet concrete .45 to .8
rubber on dry asphalt .35 to 1.2
rubber on wet asphalt .25 to .8

That in addition to the extra drainage grooved concrete has with respect to hydroplaning...

Yea, it's good for those really hard and rainy times. plus if your in a slide and you hit that grooved stuff you'll regain traction and go forward. same thing with snow.