When you are starting from the from you won't have a long 7th gear because DRS usage is not very likely. So you gear it for optimum non-DRS performance (shorter).
When you are at the back and need DRS-overtakes to get to the front you would be rpm-limited likely not getting beneath the other car.
Changing the gear ratios of 6th and 7th is the most likely reason for the gearbox change in my opinion.
Maybe, as FlashMaster said to have more race setup. But, still the problem is tyre degradation. Did they try this, racing harder will damage the tyres more, so maybe he will need more pitstops then. I don't know what are rules for gearbox change, do you have to put gearbox with the same characteristic like the gearbox you change? If you can change the ratios OK, you can start 22nd, if not, to do the ratios change you need to start from the pit?
I'm not a mechanical person at all but I thought that you need to open the gearbox to change ratios and the gearboxes are sealed between qualifications and race.
Yes, I also think that they can't change it after Q start and between Q and the race(park ferme). They have to decide ratios before Q start.
Edited by ivand911, 22 April 2012 - 08:26.