Can I put a road bike tyre on a mountain bike?
I am finding it difficult to ride a Mountain bike, I feel that it may be more comfortable to change the tyre to that of a road bike, which are thinner in size.
Please advise if I can do so.
You can certainly change the tires, but there are some (rather silly) complexities so it's best to go to a good bike shop for help rather than attempt to pick out your own replacement tires.
The problem with mountain bikes is that most are "26-inch" wheels, and for 26-inch wheels the actual rim diameter varies with the nominal width, so a tire that's labeled as narrower may not fit. If instead you had a 700C (standard road) wheel then the diameter is fixed and you could use pretty much any tire that's not crazy different.
`The problem with mountain bikes is that most are "26-inch" wheels, and for 26-inch wheels the actual rim diameter varies with the nominal width` **NO**. "26 inch MTB wheel" implies ETRTO 559mm. The only time I saw a non-559 wheel that claimed to be 26" off road, it was a Repack-inspired Clunker. http://sheldonbrown.com/harris/tires/
I recommend discovering the true reason why the bike is difficult to ride. For starters, try inflating the tires you have now to 60-65 psi.
You can purchase Continental Gatorskins in 26". I used them myself on my commuter for a few years - low rolling resistance and zero punctures.
Using knobby tires at 65 psi on the road isn't going to make them more comfortable.
Not all mountain bikes use 26" wheels, which most of these comments assume. 29er bikes use the exact same diamater rims as 700c road bikes. Assuming compatability with the rim width (which may require wider tires, see the sheldon brown article linked above), you could run some 700x35 or larger road tires without much issue unless you've got really wide MTB rims. I've used an old mountain bike wheel on my cross bike with 700x32 panaracer ribmos with no problems.
They make slick tires for mountain bikes used as commuters (and fat slick tires which the air provides a lot of cushioning). Some examples are Schwalbe's fat franks or big apple's (these are more baloonbike) or Marathons . Thinner doesn't necessarily mean more comfortable - in fact, the smaller the tire, the less comfortable it will typically be (this is a function of the bike's geometry and setup as well as the terrain and tires and tire pressures though). Go to your LBS and ask them for tires for road use or commuting and they will probably point you towards something similar to the Schwalbe big apples. Currently on my mountain bike which i use for commuting, I use Geax Evolution tires since I got them very very very cheap (though something like their street runner or some of the Kenda Kwick tires are probably something better for just road use if you're cheap).
You can't just take a mountain bike wheel and put it on a road bike and vice versa - the brake mounts and what not have to match up (this has been discussed a few times on these forums, whcih you can find with search) which is difficult if they're running different sizes.
The short answer is yes (with apologies to jimrings). The long answer is that your choice is very limited (and depends on your definition of road tyre - do you mean road-bike tyre or road-use tyre)?.
You'll need to look at http://sheldonbrown.com/tire-sizing.html#width or similar for what widths are compatible, and for urban riding (debris) or light off-road tracks (thorns) I would strongly suggest a kevlar anti-puncture belt.
The thinnest of the popular kevlar slicks available in 26" appears to be the Schwalbe marathon, but you could also try the Schwalbe road cruiser (I use these on my hybrid) or continental's comfort-contact
The short answer is no. Now for the long answer...
Mountain bike and road bike wheels are different diameters and use tires that are different diameters. Specifically, mountain bikes use 26" tires and road tires use the ridiculously meaningless 700c sizing. I won't get into what these sizes mean here, but you can find more info on this site or, if you really want to dork out for a bit, read Sheldon Brown's page on tire sizing.
As Batman mentioned, you can purchase slicks and semi-slicks for 26" rims. They're not technically "road" tires - they're a bit wider and run lower pressures - but they still reduce rolling resistance. There are lots of options. Just shop around
All that said, I'm not sure what you find uncomfortable about your mountain bike tires. Mountain bike tires are typically more comfortable than road bike tires. One thing you may consider is simply lowering the pressure in your tires. The maximum pressure listed on the side is very often much higher than you want or need. You can read more about finding the correct pressure here.
More comfortable provided you're not running knobbies on pavement (esp. knobbies on a walmart bike). The noise alone (especially when the pressure is too low) makes them rather uncomfortable. I have a strong suspicion that the tires are "off road" rather than "on road" if you dont want to consider 26" slick tires as road tires (I, on the other hand, am perfectly okay with counting these non 700c tires as road tires).
There are road bikes made with 26" wheels. Terry makes a bike with 650C tires/wheels -- 26x1", and the same ISO diameter as the Schwinn S-7 26x1-3/4".
I guess it is important to note that a 26x1-3/4" is not the same as 26x1.75 tire in bicycle speak (http://sheldonbrown.com/tire-sizing.html is useful but not complete). The Surly Long Haul/Disc truckers do ship with 26x 1.75 tires as an option (and are a requirement on sizes under 5x cm i think where i think x=6).
This answer seems to be extremely outdated, in the age of 700c 29ers. And no-one can post a real up-to date answer, because it is closed as a duplicate of something very different. The question whether a certain type of bike can accommodate a certain type of tyres is useful, it does not have to be a duplicate of a question about how to make that kind of bike more comfortable on roads by other means.
@VladimirF I don't disagree with you. The answer has aged poorly, as has the question it is linked to. I recommend doing two things: 1) Downvote this answer and, if appropriate, upvote one or more that you think is/are better. You won't hurt my feelings. 2) Vote to reopen the question, if you think the closure is incorrect. Five reopen votes will reopen the question. I'm not going to do so because my mod vote reopens it immediately, but I won't override community consensus.