The springs used on coilovers are normally always a straight line in characteristic.
Most "normal" lowering springs (decent ones) are not. Then it's the more they are compressed, the harder they get!!! (you can see that..... the spring has windings close to each other and also windings that are more "stretched out")

The helper springs on coilovers are just to make sure that the spring isn't loose when the car is lifted. (ie. in a Dukes of Hazard syle jump) Loose spring when lifted is MOT failure........

This helper spring is fully compressed in a range to 50-100 kilograms. That means it is always fully compressed when the car is with it's weight on it! That way it can't be doing anything to the handling!!!


Greetings,
Mark