I've always owned a mountain bike mainly cause they are CHEAP and I used to ride my bike rarely.

Nowadays I've gotten very addicted to the sport and still ride my mountain bike. My brother tried a road-bike the other day and said it is SOOO much easier to pedal, the efficiency is much better. I figured that is from lower resistance from the thinner width of the tires, correct? Or is it because the bike is lighter? I never understood how the bike being, let's say 10 pounds lighter would be the greatest cause of the greater speed and efficiency considering people like me weigh 170 pounds.

So is it the wheel width that is contributing to the road bikes efficiency the most? Is it the actual TYPE of tire that has a lower rolling resistance? Is there even a big difference between tires?

I'm just wondering because if 700 is more efficient than 26" MTB wheels, then wouldn't our range be a lot better on our electric bikes if we use those wheels instead?

Anyway, just a lot of thoughts going through my head... thanks in advance.