You never know anything unless it’s been measured. That’s the rule any engineer lives by.
Most people think of suspension systems and tuning them as some sort of voodoo or black art. The #1 problem with these folks is that they really never understood the role that springs play in the system or how springs work in a deep and meaningful way. If you are really solid with springs, suspension becomes much much easier to work with. Knowing this, if somebody starts telling you they are a ‘suspension tuner’ and they lack a spring scale, just start laughing.
We were out setting up Mary’s coil shock for the 2012 season. It’s essentially new out of the box other than the PVD eccentric reducers and spring perch shims. Cane Creek sent it to her for the Santa Cruz V-10c with a 300 lb/in spring. Getting out on the bike in 8″ travel mode showed that this spring was far too soft for any sort of real riding. She definitely needs a stiffer spring.
In ordering a new spring we need to actually know what she has. The labeled rate on the spring (especially on a bicycle spring) should never be believed. Bicycle springs can be off up to 20% while motorsport springs are usually withing 1%. We use a spring scale to measure this.
This spring was in fact a 286 lb/in spring measured between 0.500″ and 1.500″. A 4.6% low spring. Not bad really compared to many I’ve seen. I typically rate the spring every 1/4″ but we were in a rush this morning and we just needed a ballpark for ordering tuning springs. Measuring the spring every 1/4″ through the rated stroke will show when and how the spring starts going progressive.
We will order a 350 and 400 spring for next weekend. They will be rated so that we know what we are working with and what direction we need to go next. The goal is to find the stiffest spring possible that allows for full use of the suspensions travel and a ride height that is usable with just enough preload to keep the spring from rattling.
Later, Mary will get a titanium spring, but that is only after we have proven the correct rate spring in steel at 8″ and 10″ configurations.
I’ve written more about springs here.