Replace the timing belt on a Ford Focus that has operated under normal driving conditions for most of its life at 100,000 to 125,000 miles. A Focus that has been extensively driven on the highway, off-road or at low speeds may need its belt changed a little sooner.
A damaged timing belt needs to be replaced ahead of schedule because it interferes with the operation of the car's engine. If a timing belt becomes worn or jumps a tooth on the sprocket it rides on, the car's engine may stall or the vehicle may be slow to accelerate. Even a relatively small collision can be enough to knock the timing belt out of sync.