Belgian Grand Prix in 90 seconds
By Mark Hughes
BBC F1 commentary box producer
So Formula 1 pitches up at Spa for the Belgian Grand Prix and suddenly the competitive order is radically different.
A Force India starts from pole ahead of a Toyota and a BMW, the Red Bulls are eighth and ninth on a track on which they were expected to dominate and neither championship leader Jenson Button nor Lewis Hamilton even graduate into the top-10 run-off.
Whatever was that all about?
Before looking at the possible explanations we need first to recognise that, actually, the Red Bull probably was the fastest car of the weekend but its potential wasn't seen in qualifying thanks to lack of practice running time for Mark Webber and an error on Sebastian Vettel's best lap.
In the race, Vettel was able to lap a full 0.4 seconds faster than either Giancarlo Fisichella's Force India or the winning Ferrari of Kimi Raikkonen.
The Toyota, too, was probably marginally faster than the Force India or Ferrari, with Jarno Trulli on a fuel weight-corrected pole position by a couple of tenths.
Having a fast Toyota is nothing new - they monopolised the front row in Bahrain earlier this year - it's simply against the car's recent run of form.
Had Trulli been able to make a clean start at Spa there's every indication that he could have won from the front.
Similarly, the Brawn was competitive, as shown by Rubens Barrichello's second-row starting slot, and it was only Button's struggle with generating the necessary tyre temperatures that left him out of the top-10 shoot-out in qualifying.
Domenicali pleased to get first win
What we are left with then is a Force India and a BMW that have jumped from knocking on the door of final qualifying to artificially topping it and a McLaren that went in the opposite direction.
Both the Force India and BMW had shown very real improvements prior to Spa.
At Valencia the previous week, BMW's Robert Kubica graduated to the shoot-out and beat Webber's Red Bull to eighth in the race and Adrian Sutil qualified the Force India a solid 12th.
The difference between the fastest car in second qualifying and 12th these days is typically around 0.5 seconds or less. So we are not talking about a night and day difference.
McLaren came to Spa absolutely not expecting to figure strongly, knowing that their continuing lack of fast-corner performance was not going to allow them to take up where they left off around the slow- and medium-speed twists of Hungary and Valencia.
Nonetheless, while accepting all these provisos, the Force India and BMW were suddenly a lot more competitive at Spa, at least as fast as a Ferrari, despite no major developments since a week earlier.
This is largely to do with the very different aerodynamic demands of Spa to any track F1 has visited this year so far and how that suits some cars better than others.
Spa is the first truly low-downforce track of the season, one of only two (Monza, where the Italian Grand Prix will be held on 13 September, being the other).
The long straights of sectors one and three demand that a car has good straight-line speed, so the necessary wing level for the optimum lap time is much lower than anywhere else so far this season.
However, different cars will hang on to different proportions of their downforce when wing levels are lowered. Downforce is not only derived from the wings but also from the bodies and underbodies of the cars themselves.
Each design will have its own unique point of trade-off between straight-line speed and lap time at each track, and the competitive order between the cars will vary along with the demands of a given track.
The demands of Spa being so different to the other tracks to date simply revealed that the cars have a different order of performance relative to each other when wing levels are lowered so far.
It's an amazing result - Fisichella
The change of order is not so surprising when the lap time margins between that order are so small anyway. It will not take much of a net change in competitiveness to radically change the order.
The Force India and BMW clearly hang on to a bigger proportion of their downforce than some of their rivals when wing levels are lowered, enabling them to be reasonably quick through the twists of sector two while still retaining good straightline speed in sectors one and three.
What is clear is that the season's fastest cars - the Red Bull and Brawn - have not developed much recently. The teams have been adding new aerodynamic components that the wind tunnels are telling them will add performance, but they are not translating at the track.
Meanwhile, the teams that began the season well behind, such as BMW and Force India, have been steadily adding performance of late.
That process has brought the whole field closer, close enough that just a small change in requirements - visiting a low downforce track, for example - can have an eye-opening effect on the competitive order.
As to why the Brawn and Red Bull developments have not been effective of late, that's a whole different question for some other time.
Mark Hughes has been an F1 journalist for 10 years. He is the award-winning author of several books