I think the above posts raise some good reasons.
Some guys are good over 1 lap and can't deal with the variations of a GP race.
Others don't shine in quali but deliver consistently in the Race.
The variance you speak of is big though!
Also:
Qualifying setups vs Race setups.
“It’s all a question of tactics and being able to pass your rivals in the race. Being slower in the tight sections is no great penalty because it is not easy for other drivers to pass you there.” Alain Prost.
Some drivers will have a separate race and qualifying setup, many do not. The theory is that in qualifying with low fuel and possibly options your corner speeds and top speed will be higher than in the race setup. This will impact gearing and wing decisions. Also while your qualifying setup is to find the ultimate solo lap time conversely your race setup may be optimized for certain overtaking points on a given track. Take Valencia for example: long fast straights and slow corners. In such a race one may decide that there will be overtaking opportunities on the straights that suit a low wing setup. One may also decide that the aero influence is negligible in many of the corners and that the slow corners don’t represent an overtaking opportunity or threat. The decision may be made to move away from the setup that gave you the fastest lap time to one that makes you faster on the straights. You will then need to manage the inherent compromise in the corners.
When one thinks this phenomena through it becomes clear that the characteristics of the track will dictate whether it (two setups) is a strong option. In the authors view tracks that are consistently fast or offer medium to high speed corners (Monza, Spa, Catalunya, Silverstone) and tracks that are consistently tight (Monaco, Hungary) will offer the least to gain from divergent setups. This is due to the fact that what gave you the fastest qualifying time will be needed in the race. At Monza for example you need ultra high speed in qualifying and the race. At Spa you need a balance of high speed and good high speed (aero influenced) cornering.
On the other hand tracks that feature a big variety of some high speed sections and low speed (mechanical grip) corners (Valencia, Marina Bay, Abu Dhabi) will potentially offer gains from divergent setups from qualifying to race. It’s not a cut and dried topic and all open for experimentation-enjoy.
