I found a little explanation on wheel bearings, it helps. Thanks to Porsche NLA parts.
I have a 1957 356A coupe and I plan to service the front axles, drums and brakes. I’ve heard that the original ball bearings should be changed over to roller bearings. Why should I do that? What’s the advantage? - William Butcherson, Salem, MA.
Ball bearings have been used in automobile wheel assemblies from very early days. This type of bearing is cheap to make and is used where weight is directly downward. Some people call this a Conrad bearing (Robert Conrad–Patent 1903). The downside is that the contact area of the balls is very small, making this type of bearing suitable for mostly light weight vehicles. Although some side loads (thrust) can be tolerated, ball bearings are best for light radial loads. In our Porsche application, where the weight is light and the wheels are narrow, ball bearings have usually been good over the years. 
In modern times, wheels are wider, tires are “stickier” and we drive faster. The tapered roller bearing offers both excellent radial plus better thrust features than the ball type.  Some guys call these Timken bearings (Henry Timken–Patent 1898). Take a look at the illustration below.  Obviously, each roller has more contact surface to the cup and cone. The taper angle of the roller resists the thrust better than a simple ball. Virtually all cars from the 60s on are fitted with some form of tapered rollers
Hope this helps. From Brad Ripley