Road bike stems have raised heights and MTB stems have shorter heights, so many riders install road bike stems in their bikes to increase the height of the handle on a mountain bike for better gripping and handling, everything is possible but you need to check the width and diameter of the clamp of both road and Mtb bikes same as that of the handlebar width of the road and Mtb bikes, if the clamp diameter is matching exactly with the with of the handlebar, then you can easily replace and interchange stem between both of these categories of bikes without any issue.
Replacing and interchanging the stem of handlebars also depends on the trails where you are riding on a daily basis, more durable stems are needed for technical trails, but road bike stems are not as durable and as grippy as MTB stems, if you are riding on cross country and simple trails, then it would fine to install road bike stems in an Mtb but if you are riding on downhill trails then all the force and stress accumulates in the stem and headset of the bar, never install road bike stem in your bike for DH trails because it is risky, it will loose and wobble which is dangerous for the rider.
Drop bars of road bikes have a different diameter of stems which is 26. o millimeters but without drop bars, flat bars for both Mtb and road bike stems have 25.4m if your road bike has the same flat bar installed in your bike then you can easily swap and replace Mtb stem with a road bike and vice versa because the diameters of the handlebar for both of these stems are also the same size, but if you are converting and replacing drop bar to flat bar then it is not possible to replace stem body between them due to different width of the tube of the handlebars.
Shim Clamps For The Stem:
Shim clamps are installed above the stem for compatibility and these can easily make a good relationship between the stem and handlebar of Mtb and road bikes. wider and narrower handlebars install shim clamps to make the handlebar compatible with the stem body. you can easily install these shim clamps on the handlebar of mountain bikes to make the bar compatible with the road bike stem but if you have installed these shim clamps on the handlebar of road bikes to make the bar compatible with the mountain bike stem, then the setup will not work and handlebar of your road bike will ruin and cause damage due to non-compatibility.
Road bike stems are not as strong and durable as Mtb stems, so choosing different categories of stem bodies for the durable totally depends on the trails and the weight of the rider. the rotating torque force for the Mtb stem body is 15Nm but the handlebars of road bikes do not survive this large torque force, this value of force is for hard and aggressive Mtb trails because the steerer tube and forks of Myb are also much more durable than road bike tubes, the maximum torque force for road handlebar with Mtyb stem body is 8 to 10 Nm.
Diameter Of The Stem Clamp And Steerer Tube:
Stems body of the handlebar has clamps for adjusting with the steerer and handlebar of bikes, and the diameter and width of these clamps are different for different steerer tubes. while choosing or replacing the stem between road and mountain bikes, check the diameter of the clamp and the steerer, and also the handlebar, if these are matching with each other, then you can easily replace the stem between them.
diameter of the steerer tubes is different on tapered and non-tapered forks, you have to check your fork types, and then check the diameter of the steerer tube, and then check the diameter of the stem clamp for making the setup compatible with each other.
“1” And 1 1/4 Forks:
these are two different types of forks with different sizes, and these are called tapered forks, changing or replacing the stem body also depends on the size of the fork, first you have to make both of these sizes compatible with each other by shim clamps or finding and matching the accurate size and width of the steerer tube and handlebar of the fork for the stem body.
1 1/8 Forks:
these are new and modern discoveries, these are also tapered forks with different sizes, but if you want to replace or interchange two stem bodies of 1 1/8 size forks and steerer forks then you can easily replace them because the width and diameter of the steerer tubes for this size 1 1/8 are same for both road and Mtb bikes and the setup is compatible.
The difference in The Structure And Shape of the Stem Body:
Both road and Mtb stem are also different in their shapes based on different rotating angles. mountain bike stem bodies are straight and perpendicular to the handlebar, we can say as Mtb stem bodies have straight vertical positions but road bike stem bodies are not vertical, these are cursory and superficial, Mtb stem bodies allow the flat handlebar to rotate widely both left and right sides but road stem bodies are limited to a certain angle. angle difference is also a big issue that will change the handling and gripping of a skilled rider which is shifting from Mtb to road stem body and vice versa.
Weight of The Stem Body:
Mountain bike stem bodies are heavier in weight than road bike stem bodies, based on this difference you have to choose the accurate weight of the stem body so that it won’t affect the steerer tube of the handlebar and the fork when you are riding on the trails.
Material of The Stem Body:
Aluminum material stem bodies are less durable than steel material stems, the material of the stem body also depends on the material of the fork and the steerer tube.