MPH: Mark Hughes on...

By the time you read this, the FIA Court of Appeal will have ruled on the legality of the slotted twin diffusers as used by Brawn, Toyota and Williams in the season's first two grands prix.

Whichever decision has been reached, we are now going to get some answers as to how much of a performance benefit or hindrance KERS is, because the pattern from Australia and Malaysia was that all the KERS devices were fitted into poor-handling cars. Furthermore, the twin-diffuser cars were all fast and none of them had KERS. The only conventional-diffuser car that looked at all competitive was the Red Bull - and that didn't have KERS either. Is this all just coincidence or does KERS, as currently configured, actually cost lap time?

What is clear - as Fernando Alonso and Flavio Briatore have pointed out from the same hymn sheet - is that those teams that have devoted their development time to KERS have lost out to those who have concentrated on circumnavigating the reduction in downforce brought about by the new aero rules. "We have done what the FIA wanted us to do," protests Alonso, "and because of that are being beaten by teams that did what the FIA didn't want."

That perspective explains the divergence in performance between the two camps. But it doesn't answer whether KERS in itself costs you lap time. Looking at the fuel-tank/KERS-battery packaging of the Ferrari - with the reduced-capacity tank sitting atop the batteries - makes you wonder.

Such a layout is bound to raise the centre of gravity significantly. Even without much gas on board, the fuel weight is above the batteries. The BMW arrangement, which gets around the tank-height problem by installing the batteries upright in the sidepods, is possibly even worse.

Ostensibly, the effect of a CoG increase upon lap time can be calculated, essentially by working out how much more load the increased leverage effect of the CoG puts into the tyres, thereby depriving the car of grip. This is separate from the adverse effect of not being able to use as much ballast to achieve the ideal front/rear weight distribution for a given circuit. That too can be calculated.

Using these calculations, Ferrari, BMW, Renault and McLaren are adamant that this penalty is more than overcome by the 80bhp boost for 6.7s per lap and that KERS has a net lap-time benefit. They'd be slower still without the KERS, they say. Maybe.

But what about when you take into account the load variations on the tyres resulting from the airflow stalling in the diffusers, which it is wont to do in the conventional-diffuser cars, amplified by the weight of KERS? The slotted twin diffusers allow you to run a much lower ride height before encountering diffuser stall.

They can therefore be set up to give a more consistent downforce loading to the tyres. Each time the downforce stalls momentarily, then re-attaches itself, the tyres have to withstand the sudden spike loadings - and this takes a lot of energy out of them. It's the tyre equivalent of using your fuel by driving down the road alternately braking and accelerating - and you're going to run out of fuel pretty quickly doing that.

The effect of that sudden decrease/increase in load on the tyres is of course amplified by the leverage of the CoG height. So in tyre usage the KERS cars have the worst of both worlds: a conventional stall-prone diffuser and a high CoG. It's probably not a coincidence either that the only fast conventional-diffuser car, the Red Bull, has pullrod rear suspension, which lowers the CoG height significantly.

Seeing KERS and non-KERS cars with the same type of diffusers in the coming races should provide some answers on the true potential of the energy recovery devices.