What do you guys mean by 'soft'? The reason I ask is that in this type of fatigue, it is usual for the material to harden due to the work is it doing. It's known, unoriginally, as work hardening. The other thing that can happen is hardening through age (known as age hardening!) which will have the same effect on the working of the spring.
The effect you see is that the spring gets shorter, and that the rate actually goes up as it becomes less resilient. However, a lack of travel and the stiffening of the spring will change the handling, and fitting new ones will restore previous performance.
So, I'd be interested to know what you mean by 'soft', because the mechanics of the materials means that they can only become less resilient, not more; harder, not softer. I know that on full-size cars, guys refer to springs having 'collapsed' as this is the effect of the reduction in their length. Whilst we contantly adjust ride height, and don't notice the reduction in length as easily, you can always spot a road car with collapsed springs! Thanks in advance for any information that might help me explain the issues a bit better.
