Can a wide tire be mounted on a narrow rim?

The short answer is that we would NOT recommend mounting ANY tire to a rim that the tire manufacturer does not suggest.

In our experience, mounting wide tires on narrower than recommended rims can lead to instability, poor grip, and overall negative handling issues.

The width of the rim will influence the width of the tire. A tire mounted on a narrow rim would be narrower than if the same size tire was mounted on a wide rim. The photo below is an example of the same size tire mounted on two different-width wheels. 

We have customers (primarily in the V-Twin world) who do this with no problems. However, most instability issues, especially high-speed instability, we encounter trace back to this combination. Mixing bias-ply and radial tires on the same motorcycle will also cause these same issues.

Another thing to consider is clearance. Will this change affect clearance areas like the fender, the belt, the swingarm, brake bars, etc. 

These same principles apply whether you are running alloy wheels or carbon fiber wheels. So, please be sure to check your tire manufacturer's suggested minimum rim width specifications before installing.