Rigidbody AddForce doesn't matter what rotation

I have a rigidbody, and am applying

rb.AddForce(transform.forward * speed);

This moves the rigid body forward as expected.

However when I rotate the rigid body to 90, so it is facing sideways, it still moves the same direction.

I basically want to apply the force to the back of my rigid body, so it will move whatever rotation it is now facing.