The rack-and-pinion steering gear box has a pinion, connected to the steering column. This pinion runs in mesh with a rack that is connected to the steering tie rods. This gives more direct operation.
Both the pinion and the rack teeth are helical gears. Helical gearing gives smoother and quieter operation for the driver.
Turning the steering wheel rotates the pinion, and moves the rack from side to side. Ball joints at the end of the rack locate the tie-rods and allow movement in the steering and suspension.
Mechanical advantage is gained by the reduction ratio. The value of this ratio depends on the size of the pinion.
A small pinion gives light steering, but it requires many turns of the steering wheel to travel from lock, to lock.
A large pinion means the number of turns of the steering column is reduced, but the steering is heavier to turn.
Ratios vary, depending on the type of vehicle.
But in each case, the ratio is the same for all positions of the wheels. It is a fixed ratio.