You will only find this information on bikes that were specifically designed for use with both tire sizes. On the models with one tire size, frame and fork simply don´t accept much wider tires even with a 650B wheel. You might only gain about 2-3 mm more in tire width, while keeping a minimum of 6 mm tire clearance. Using a 650B tire with very little additional tire width is not very beneficial and would drop the bike significantly, reducing pedal / crankarm – ground clearance and altering the steering geometry.