When designing your spring you are also trying to meet certain working loads. When it comes to compression springs, for more force, you can decrease the outer diameter, increase the wire diameter, reduce the amount of coils, or increase the free length to get more force through more travel. To get less force out of the spring, you do the exact opposite. Increasing or decreasing the free length isnít always an applicable option but if your spring has the room, it is definitely a helpful resource.
For extension springs you must follow the same process except that in this case, to change the number of coils, you must adjust either the body length or the hook length. Shortening the length inside hooks to increase force through more travel isnít very recommended but if you have the room and have no more options, go for it.