| You should use the rim width specified by the tyre manufacturer to get the proper contact patch.
Different designs have different suitable rim sizes. If you use a rim width outside the recommended size range you loose a lot of the engineering that goes into a tyre. Todays tyre designer develops a new design using finite element analysis to balance tyre carcass construction, profile, sidewall stiffness, stress, temperature, wear, spring rate, tread compound and pattern - as well as contact patch. At different lean angles and uneven road surfaces, all of these factors affect camber thrust (grip.) Size of the contact patch is important but the stability of the patch is equally important.
Profile design is just one of the ways to improve the tyre’s performance. It allows control over the shape of the contact patch and the degree to which it changes as the bike leans over. A longitudinal-oriented footprint gives acceleration and braking grip, a lateral footprint gives sideways grip. You need a bit of both, and a good profile will give it to you.
Of course you’re at liberty to mess with this equation, or take other rider’s suggestions, but with so many other variables such as suspension settings and even just tyre pressure, why not take the tyre manufacturer’s recommendation on rim width?  | 
Shazaam!
Threaded Mode