IT ALL concerns the design of the rear diffusers of cars belonging to Formula One's best-performing teams so far this season - Brawn, Williams and Toyota.

Yesterday, officials from Formula One's ruling body FIA went into a closed-door hearing with the above trio and Ferrari, Renault, Red Bull and BMW Sauber who are appealing against the legality of their diffuser designs.

They are expected to hand down a ruling early today.

On the Brawn car for example, the way this diffuser is built into the design simply looks like underwear.

If you look at our infographic, the hole indicated - as created by a specially-designed deformable flap - increases the speed of airflow so it helps push the car down for more downforce and better grip.

Toyota and Williams have their own design interpretations that differ slightly from Brawn's 'underwear-like' diffuser.

In short, rear diffusers this season were supposed to get smaller, but the 'diffuser trio' have ended up with bigger ones, exploiting a little loophole in the season's new laws.

And the belief that this helps give extra crucial tenths of a second are what almost the entire Formula One grid are against.

For Brawn, Toyota and Williams have - in practice and in race trim - almost left the field behind in the two Grands Prix so far this season in Australia and Malaysia.

A further complaint is that these teams' diffusers limit the opportunities for cars to pass, in contrast to rules that encourage overtaking this year.

But BMW Sauber have admitted that they are already working on a similar diffuser design, before yesterday's appeal hearing.

BMW Sauber team boss Mario Theissen said: 'Two of the three teams with a two-stage (double-decker-styled) diffuser are clearly quicker. Brawn as No. 1 and then Toyota.

'Everybody (is working on their own version). We cannot sit back and wait until the Court of Appeal is held and we have a decision. We have to work on it and we are spending money on it.

'The sooner it is sorted out the better. But you cannot expect to make up for such a big gap within a few weeks. And it is clear that the teams that have it already are developing their cars as well.'

Enormous impact

In the meantime, Ferrari's ex-world champion Kimi Raikkonen said: 'The FIA's Court of Appeal's decision will have an enormous impact on the championship.

'You just need to analyse the performance in Malaysia to understand that we're losing a lot compared to the best cars. You can see that especially in the middle section, where downforce is really crucial.'

If the protesters win their appeal, the FIA has two options.

It could allow the results of the first two races to stand, with Brawn, Toyota and Williams forced to alter their cars starting from Sunday's Chinese Grand Prix, or they could remove any points won by those teams in Australia and Malaysia.

Brawn's Jenson Button has won both races and his team leads the Constructors' Championship with 25 points, ahead of Toyota on 16.5 points.

The other eight teams have only 17 points shared among them and Ferrari, the reigning constructors' champions, are yet to get off the mark.

If the judges rule the diffusers are legal, then the seven teams who are running without them will try and incorporate the design into their cars.

But doing it at this stage of the season will be tough, as they would still lose some ground in the next few races trying to find the optimum set-up with new rear diffusers.

The hole dispute

BRAWN have a different-looking central channel to their diffuser that makes it look like 'underwear'. The shape of the deformable structure creates a double-decker design. To work properly, this section of the diffuser needs to be fed by air.

Highlighted above, you can easily see the holes indicated in the 'underwear-looking' design. The holes increase the speed of airflow towards the higher rear section, where it expands and creates more downforce. Other teams are arguing that the presence of the holes is against the rules.