**according to a ground observer**, the bottom of the tread is stationary, the axels (and the body of the tank) are moving to his right at .866c, and the top of the tread is moving to his right at 2 x .866c. Can't you understand that the top of the tread is moving to the right of the ground observer at twice the speed of the tank body?

**According to an observer inside the tank**, the top of the tread moves forward at .866c and the bottom of the tread moves rearward at .866c. Both top and bottom would be contracted by the same amount,

**according to the tank observer.**

The observer on the ground sees a different scenario. He sees the bottom of the tread at rest with the ground, the tank moving to the right at .866c, and the top of the tread moving to the right at twice the speed of the tank itself. The tank tread moves in different directions at the top and bottom. This creates the paradox in the ground frame. The ground observer does not see the top of the tread and the tank moving to the right at the same speed. The tread still moves relative to the tank body and its axels.