The titles may be decided, but the Formula One teams have worked as hard as ever to prepare for the upcoming Belgian Grand Prix at most of the drivers' favourite track: the exciting Spa. Atlas F1's Technical Writer Will Gray previews the event

Click here for a track map of Spa

One look up to the skies may usually be the best way to tell if a race, qualifying or practice session will be wet or dry, but at the classic forest-clad circuit of Spa-Francorchamps that is not the case.

The unpredictable weather system in Belgium's Ardennes forest means that weather predictions are critical and, perhaps more difficult than at any other circuit on the Grand Prix calendar. That is why the teams will be putting their complicated satellite weather systems to frantic and unrelenting use as they study weather patterns to second-guess what is coming.

Maybe it will not rain at the circuit this weekend. But Formula One, by the law of averages, is surely due a wet race soon. No place would expect it more than Spa - but even if rain clouds do gather, things are still not that easy. You see, with the 4.330 mile-long circuit, the longest currently used in Formula One, chances are that it will be raining on one side of the circuit and not the other.

At the end of the day, it is really down to a mixture of pot luck and good judgement to get decisions right - and for that reason, it could be Ferrari's rivals best chance in a long while to take the fight to the Italian team. Even though Ferrari are clearly technically superior, the Williams package will suit the flowing circuit, and they could hit back, especially as they will be introducing new chassis developments for the race.

The circuit itself is a fast, medium-downforce track, with several long straights combining with slower corners like the almost-stationary 'bus stop' chicane. But, of course, the Spa circuit is generally known for one thing, and that is the awesome Eau Rouge corner. Some take it flat, some don't dare, and some don't have the car to even take it on.

But one thing is certain, and that is the critical corner leaves the cars having to heavily compromise on set-up for the rest of the circuit because, due to the loadings involved, it is the one which defines much of the car's set-up requirements.

Because the cars drop downhill at high speed as they head into Eau Rouge, then begin to climb back up the hill as they exit it, the G-loading which both the cars and drivers experience is immense. The only way the car, which runs very low to the ground, can cope with the massive compression, or downward forces which are created is to have a much stiffer set-up than is usually used.

However, that creates great problems when the cars come to the 'bus stop', because the two corners are so dramatically different. It is important to go as fast as possible through Eau Rouge, but many teams believe the 'bus stop' is where most time can be gained or lost through set-up.

For that reason, many will opt to go for a set-up which will see them have a slower speed through Eau Rouge but will allow a neat performance through the left, right, right, left 'bus stop' section which bears similarity to Monaco's swimming pool section.

Blanchimont is another classic corner in the sweeping, undulating track, a fast left-hander which is also important to get right, but to balance that out there is the very slow La Source hairpin, leaving the teams with a difficult set-up compromise.

Added to that, because the circuit is used as ordinary roads throughout the rest of the year it will constantly improve in grip as the weekend goes on. However, if it does rain that could wash the track 'clean' and change the grip levels again, leaving engineers with even more problems to solve.

So, all in all, the circuit requires a car that has good engine power, is efficient at medium levels of downforce and has a suspension system which can cope with the compression in Eau Rouge without losing too much at the 'bus stop'.

As for strategies, that will very much depend on the weather. If there are any threatening clouds when the qualifying hour looms expect cars to come straight out and put in a banker lap before waiting to see if temperatures will rise. However, if it is clear skies overhead then all teams are sure to wait until the dying seconds to make their push for pole.

The race last year was a clear two-stopper, with most of the top six having taken that strategy with great success, so it is quite likely that, without rain, that will be the way to go again. But if there is rain, then just keep watching the skies.