Last Sunday, Champ Car had its best race of the season, in Denver, Colorado, with more overtaking than seen in an entire Formula One season.
The reason was that Bridgestone's ultra-sticky street-course red-walled tyres simply weren't up to the task of dealing with Denver's bumpy mix of asphalt and concrete for a sustained period of time. To quote the winner AJ Allmendinger, they 'turned to junk' after 10 or 12 laps. To be fair to Bridgestone, though, they hadn't brought alternate tyres to Denver last year so they had no experience of the 1.657-mile course's tyre-shredding tendencies.
The side-effect of ultra-soft tyres is that there is an excess of rubber marbles off the racing line. That means if you're forced off line by a passing car, not only do you slide wider, it also takes a good couple of laps to clean your tyres and regain 100 per cent grip.