Each piece of the ring is longer as measured by an inertial observer comoving
We, at this problem, don’t care for a “comoving” inertial observer. We care for the stationary observer in the center, who first see stationary and then rotating torus, which should contract. But only in the direction of moving.
We, at this problem, don’t care for a “comoving” inertial observer. We care for the stationary observer in the center, who first see stationary and then rotating torus, which should contract. But only in the direction of moving.