Lotus still favourite despite double DRS decision

The layout of Spa is perfect for maximising the benefit of Lotus's new double-DRS drag-reduction system. But the nature of Spa leaves the team in a horrible dilemma, as the notoriously capricious weather of the region rained both Friday practice sessions out, leaving the team unable to assess the new component.

Sources in the team believe the rear-wing-stalling device - tried out in practice but not raced in the previous two events - could be worth as much as 0.5s around the long Belgian track. But it's crucially important that the team is able to fine-tune the threshold at which the air pressure switches the airflow.

The principle behind the device is a 'fluidic switch', whereby airflow through tubes running from either side of the engine airbox to the rear of the car switches at a set air pressure between two exit routes.

At lower speeds the flow is directed over downforce-producing devices such as the brake ducts and the diffuser. As the car's speed builds, so the air pressure in the tubes increases until reaching a pre-set point at which the flow switches to travel through the channels connecting the engine cover to the rear wing, exiting in the wing endplates and blowing across the wing.

This reduces both downforce and drag. It is believed to work regardless of whether the conventional DRS flap is in use, thereby bringing a performance advantage at all times.

As such, it is crucially important that the speed at which the flow switches is higher than the speed of the fastest corner - otherwise the driver is set for a nasty shock as the downforce suddenly decreases through the 160mph Pouhon turn. The cars exceed 180mph for extended periods on both the major straights of the track. So the aim would be to have the switch activate at some point beyond 160mph - but with a significant margin built in.

The air pressure entering the system naturally varies, and to a significant extent. Changes in atmospheric pressure from both the weather and the extensive changes of elevation of this track, not to mention the pressure change resulting from the slipstream of another car, can mean variations of up to 20 per cent.

This would vary the car speed at which the airflow would switch. For this reason the system will require very specific setting up - and Friday's weather leaves the team with just Saturday morning's practice session in which to ensure its effective and safe operation. This was not deemed feasible and so the system's introduction has been postponed until Monza next week.

But all is not lost. Even without that device, the Lotus remains a hot favourite around this place. Several times this season the Lotus E20 has been the fastest car on race day, but thwarted by not being able to qualify on pole.

The gentle tyre usage which is such a boon on Sundays means that it is not aggressive enough on the rubber for ultimate one-lap qualifying pace. In Hungary, after fending off first one Lotus, then another to win, Lewis Hamilton pointed out that had it been a track on which overtaking was easier, the result would likely have been different.

The long, fast corners of Spa should allow the Lotus's tyres to reach optimum temperatures even in qualifying (the forecast is for dry qualifying) and even in standard form its aero-efficiency in low-downforce trim appeared to be the best in Montreal. Therefore it arguably comes into the weekend as favourite even without the device. Put into that mix the king of Spa, Kimi Raikkonen...