Updated with quotes from MotoGP front row qualifiers Marc Marquez, Valentino Rossi and Jorge Lorenzo.
Michelin has withdrawn BOTH of its planned rear tyre compounds ahead of Sunday's MotoGP race in Argentina.
The decision has been made on safety grounds following a scary incident for Scott Redding during final MotoGP practice in Argentina.
A new medium rear, with a stiffer construction, will now be introduced on Sunday.
"The reason both current tyres [medium and hard compounds] must be withdrawn is because they are both of the same construction, meaning that there is a possibility of a similar failure on the harder tyre," said a statement.
"Michelin's new rear tyre to be introduced from Sunday is of a harder construction, and will cope better with the hard strains and temperatures put through it – albeit at the expense of lap times."
An extra 30 minute practice session will be provided, in addition to the 20 minute warm-up, to give teams and riders more time to find a set-up with this new tyre - although if weather reports prove accurate they could be using wets anyway.
Debris exploded from the rear of Redding's Pramac Ducati during FP4, the Englishman fortunately keeping control as he parked his damaged GP15 in the gravel.
The session was immediately red-flagged yet bizarrely, given that marshals were seen carrying pieces of tyre from the track, restarted soon after. The session was then stopped for a second time due to 'safety conditions', to examine Redding's machine.
With only four minutes left on the clock, and since the following qualifying sessions involve only short runs on new rubber, no restrictions were placed on tyre use for the remainder of the day.
But while it was rumoured that the favoured medium tyre would be withdrawn for the race, few predicted that the hard would also be removed. It was later revealed that Redding's tyre was "a medium compound with seven laps on it". It is still being examined by Michelin's technicians to determine the cause of the fault.
The Englishman's incident revived memories of the huge accident for Loris Baz after a rear tyre failure during pre-season testing at Sepang.
On that occasion riders were also allowed back out soon after, only for the session to be stopped again and tyre withdrawn. A puncture was later deemed to have caused the 180mph main straight accident, but there were also rumours about tyre pressures, prompting sensors to be made mandatory.
Argentina is Michelin's second event since taking over as MotoGP's exclusive tyre supplier from Bridgestone. But unlike for round one in Qatar, there has been no winter testing at the circuit prior to the race weekend.
Honda's Marc Marquez has qualified on pole for Sunday's race, ahead of Yamaha team-mates Valentino Rossi and Jorge Lorenzo. Speaking before the tyre change was revealed, the trio said of the Michelin issues:
"If you are not careful in these long corners the tyre temperature is getting very high. Especially my bike, the others I don't know, but looks like also Ducati because they have a lot of torque," commented Marquez.
"Baz and Redding are heavy riders too. So maybe they force the tyre more and get more temperature. Because if I compare my temperature with Dani [team-mate], Dani is much lower."
Rossi added: "Yes, is some different factors. Looks like the Ducati spin quite a lot, but especially this problem happen to Baz and Redding that are the tallest and maybe heaviest riders on the grid.
"The other story is about the [tyre] pressure. We hear that some teams play with the pressure, for have a bit more grip, but we don't have any official confirmation. Also today is the same; at the beginning they say about the pressure, but at the end they stop us because they don't know.
"So maybe it is because you are close to the limit and if you exaggerate, [this] can happen. But yes, for sure Michelin have to work because it is very dangerous."
Reigning champion and Qatar winner Lorenzo was more succinct: "I don't know what is happening, but I think it doesn't matter the weight of the rider or the pressure - this shouldn't happen in MotoGP."
By Peter McLaren