By Andrew Benson
Just as Formula One appeared to be getting itself back on the right track, it has gone and shot itself in the foot.
Montoya and Williams have benefited from their Michelin tyres
After attracting headlines for all the wrong reasons in 2002, this year's scintillating championship battle has grabbed attention for all the right ones.
And yet, as the title fight reaches a thrilling climax with three drivers separated by two points with three races to go, the sport's governing body risks throwing all the good work away.
The FIA has played a substantial role in improving F1 this season with the series of rule changes it introduced over the winter, but its latest threat to tinker with the regulations is one move too far.
It does not help that it is to do with tyres - a subject most people find boring despite their importance in influencing a racing car's speed.
That means all but a few will fail to appreciate the seriousness of what the FIA has done by issuing a ruling which calls into question the legality of the Michelin tyres used to such great effect by Williams and McLaren.
It is impossible to overstate the potential impact of the FIA's letter to the teams suggesting that the Michelins might in some circumstances be too wide.
Schumacher has been struggling for grip in his Ferrari
The doubt that the letter has created in the minds of those in F1 is typical of the sort of woolly ruling that has undermined the credibility of the sport for years.
McLaren and Williams have for the best part of a decade pleaded for "clarity", "consistency" and "transparency" from the FIA in the working of its rules - and this is an example of why.
Under the new ruling, a tyre that would have been perfectly acceptable for the last two and a half years could suddenly be declared illegal at the next race, the Italian Grand Prix on 14 September.
And to avoid that risk, Michelin may have to design completely new tyres for Monza.
A cynic - and there are many in F1 - would say this new interpretation looks like it has been designed to help Ferrari's faltering title hopes.
The FIA's new line of thinking came about after a complaint from Ferrari and Bridgestone.
It is certainly true that Williams' Juan Pablo Montoya and Kimi Raikkonen of McLaren have been able to revitalise their title chances because their Michelin tyres have been superior to Bridgestone in recent races.
But, as Ferrari themselves have said, it could easily turn around - some cooler weather or a bit of rain would immediately swing the advantage back towards Ferrari. And in any case Michael Schumacher, for all his problems, is still leading the championship.
Either way, that is what F1 is about. Sometimes you have an advantage and sometimes you do not - and you have to take it on the chin and get on with it.
McLaren, Williams and Michelin did not complain when Ferrari and Bridgestone were dominating in 2002. They accepted it and worked on improving their product for 2003.
But let's assume that there are no suspicious motives or dastardly intentions in this new ruling.
In that case, how can the FIA justify changing overnight an approach to assessing tyres that has stood for more than two years?
The tyre rules in F1 have long been a farce.
It is bad enough that they have to have grooves on them as a means of restricting grip - and therefore danger - to acceptable levels.
But the difficulty of policing the rule forced the FIA to abandon the idea of stipulating a minimum groove depth on a used tyre.
Now the FIA's letter adds yet another level of unwelcome subjectivity into the policing of F1's rules.
As one engineer from a leading Michelin team put it after the ruling: "It is fraught with difficulty. The tyre has been pronounced legal when new. But obviously as a tyre moves laterally in cornering different parts are in contact with the track.
"As the tyre goes left and right, do you have an area bigger than 270mm being used? You probably do. But tread width has never [before] been defined as what you use. Any tyre will deform and the contact patch get bigger. But how do you prove how much of the tyre was in contact at any one time?
"The FIA has chosen to do this. You can only guess at why and what motives they have.
"As I understand it, most of the Michelin tyres in Hungary would have been legal. But at high-g circuits like Silverstone there is evidence that more of the tyre was used. Monza could be a problem.
Michelin may have to redesign their tyres because of the new ruling
"Do we want to go to Monza and have all the Michelin teams thrown out?
"I think the only reason they're doing it now is that Bridgestone weren't complaining when they were winning. I can see some sense in the interpretation - but why do it with three races to go?"
And that is the crux of the issue - however you look at it, this new approach could undermine the credibility of this year's world championship.
If it damages the performances of the Michelin teams and Schumacher wins a record sixth championship as a result, what value would that victory have?
Alternatively, if you accept that this fundamental change in the way of interpreting the tyre rules is correct, then it calls into question the result of every race so far this season.
With spectator attendances falling and F1's credibility still in the balance in the eyes of many disinterested observers, that is something the sport can ill afford.