Hr1

Its looking like I've been misunderstood. If a mtb's characteristics suit you then ride on my bicycle brother. I found an excellent post on Stack Exchange on this subject that echoes exactly how I feel re: road vs. mtbs >

"The difference is HUGE! When you get on a set of skinny, hard, fast rolling, knob-less road tires, it will feel like your bicycle has been set free. The knobs on a low pressure mountain bike tire create and enormous amount of drag, when you no longer have to push against them the difference will be unbelievable.

You may also notice you are no longer riding with your chest stuck out like a sail. You will find the new, sleeker, aerodynamic profile allows you to maintain your speed with much less effort.

You will also notice the ride on the skinnier, harder, road bike tires is much rougher going over bumps and potholes. This drawback is well worth not having the drag. You may compromise by getting a fatter tire than allows for lower air pressure and gives you more cushion but I prefer the reduced drag hard and skinny tires give you.

You will probably notice the road bike is lighter and with your lighter bike and less tire drag it is much easier to accelerate on.

Going up steep hills you will probably notice the gearing on the road bike is higher and may miss the lower gearing unless you road bike is equipped with a touring gearing (3rd smaller inner ring).

You will probably not notice the lack of tread, even on gravel bike trails. For the most most part the tread is not necessary on gravel bike paths but if you corner hard in gravel you will notice that your wheels wash out much easier, so take extra care when cornering.

If it's a traditional road racing type setup, you will notice the handlebar and braking setup is different and that it's even a little harder to stop. At first you will also find shifting is a bit confusing and may take a little time to get used to.

You may also find your riding position is a little less natural and a little less comfortable.

Get a road/commuter specific bike. You wont regret it."

Here's another >

In regards to the speed it really depends on the rider as much as it depends on the bike. I do frequently 30 to 50 miles social rides on the weekend and and I keep up on my 26" MTB. The only times I'm in real disadvantage is long gently sloping downhills where I simply don't have high enough gears.

You will notice 3 major differences right away, with other difference you can optionally implement in the future.

1. Road bikes generally are much lighter than mountain bikes. Less weight means you can go further or faster with the same amount of effort you put into your mountain bike.
2. Road bikes have much narrower tires (compared to a mountain bike) with much higher pressure. This means you have much less rolling resistance on a road bike. Once again, you can go further or faster with the same amount of effort you put into your mountain bike.
3. Your riding position on a road bike is much more aerodynamic than it is on a mountain bike. Thus you can go further or faster with the same amount of effort you put into your mountain bike.

Those are the stock differences. Optionally you can:

1. Add toe clips or cleated pedals to your bike. Locking your foot to the pedal increases the efficiency of your biking. This can make it another 10% easier to ride your road bike.
2. Add aero bars- if you bike in the wind often, or ride fairly fast, adding aero bars gives you an additional biking position with lower wind resistance. This can make it another 10% easier to ride your road bike.

One last quote:

I have now had a road bike for 3 days since i transferred from mountain biker to road biker. I've done just over 50 miles and my experiences so far would be both bikes have pros and cons. The mountain bike is a LOT slower. The width of the tyres being thicker means more surface contact with the road and it slows you down and requires way more effort to ride especially uphill. The road bike i have, has thin tyres and the speed difference is amazing. The only drawback i have found is that without a suspension, you really feel every tiny bump/divot in the road and on long rides this can become very uncomfortable in your back/lower body/arms.The mountain bike protects you much more. Your body position too needs getting used to. Leaning forward rather than sitting up straight is a bit weird but again, i'll get used to that. Overall though i'll be sticking to the road bike, you'll love the speed difference.