Vertical bolt = less optimal. The reason is the tube walls in the 12:00 and 6:00 locations (top and bottom areas) are effectively the primary tension and compression members of the tube, and the 9 - 3:00 areas are the shear zones.
In other words, if the tube was an I beam, you'd be putting holes right in the cap strip flange of the I beam where the tension ...
"Wheel pants" is a common term for these wheel fairings, at least in US usage, which serve to reduce drag. They have also been called "spats", though that term has traditionally been reserved for something much larger, at least in US usage.
How can drag induced by the landing gear be reduced?? -- see all answers
What is "spatted ...
Those are called speed fairings.
They make the shape over the tire more aerodynamic and reduce drag, thus increasing airspeed and fuel efficiency.
This is a page in a Cessna 172R information manual that comments on the differences in performance when they are installed.