The MotoGP riders will not have the additional soft front tire at their disposal for the Argentinian Grand Prix. In a meeting of the Safety Commission on Friday night, the riders agreed that they did not need the tire, as the current allocation of three fronts was sufficient for safety purposes.
The decision is unlikely to make much of a difference to most riders. With rain expected on Saturday for both practice and qualifying, the riders would not have been able to use it anyway. That would have left them with the option of trying it out during morning warm up, but actually running it in the race would have been a big risk based on very little data in Argentina.
The additional tire is basically the prototype tire which the MotoGP riders used at Valencia at the end of 2016, which uses the 2017 profile but a stiffer carcass than the current tire. Though it worked well in Valencia, Argentina is a very different track with a lot more very fast corners, which stresses the tire differently. Getting it to work properly would have required more work than just a brief session.
The news of the tire withdrawal, which first appeared on the French website Paddock GP, is partly a result of a customs strike in Argentina. The tires were held up in customs, and did not arrive at the circuit on time on Friday. With so little time to test it, the riders decided not to use the tire. The additional front is outside of the normal allocation of tires, and additional tires are normally only used for reasons of safety, such as when Michelin is uncertain a tire will last the entire race distance. However, all three existing front tires were judged to be performing well, and so with no safety grounds to allow it, the riders decided to postpone using it. The tire will be trialed once again later this year, either at the next race in Austin or at the post-race test on the Monday after Jerez.