If you place the ORs of the water pump directly in contact with the axle, not letting them rest and adhere to the pulley to be mounted on the axle, you will obtain an extension of the transmission ratio of the motion between the axle and the water pump. The (theoretical) consequence is that in doing so, the water pump will turn less frequently with the same number of axle turns. A lower number of turns of the water pump means the water turning more slowly in the system, thus remaining longer in the radiator, with consequent greater cooling of the same useful above all on fast tracks with long straights. However, what is not taken into account is that the OR, in direct contact with the axle, already starting at a speed of 70 km/h, starts to slip. In doing so, the O-Ring no longer correctly transmits motion to the water pump which excessively reduces the number of turns and stops cooling the water properly. So you get the exact opposite of what you wanted to achieve. Therefore, my advice is to always install the pulley on the axle to optimise the pumping operation. I certainly recommend the use of a pulley with a reduced external diameter on fast tracks.