RecceDG

My new Norco Faze has an FSR-style suspension with two shock mount holes on the link arm. One is for 100mm travel, the other 120mm.

It came from the shop in the outboard (100mm) position.

I cannot for the life of me figure out why that position even exists. Less travel for the wheel and more weight for the rocker link (it has to be longer to accommodate the longer lever)

So why in the world did Norco go out of their way to provide a less travel option and pay a weight penalty to do it - and set that up as the default?

Is there some quirk of FSR links and travel that I'm not aware of?

DG

dminor 

Some people just get freaked out by having "too much travel" I think - - not realizing how efficient the Horst-Link four-bar FSR design is.

FWIW, Specialized did this to many of their FSR links - - including BigHits. Just gives the rider options depending upon conditions and how they want their suspension to react.

RecceDG

Well, this is an air spring. And air springs have sharply progressive rates based on the volume of the air chamber and the initial pressure.

In the long travel position, the rate of rate increase is going to be somewhat lower than it is in the short travel position, because the amount of movement at the shock per unit of wheel travel is lower in the long travel position.

At the same level of sag, the wheel rate will be the same in both positions, but the initial spring rate will be lower in the longer travel slot because the wheel has less of a lever acting on the shock and so needs less initial spring rate to oppose it.

So in that initial travel phase, the longer travel spot gains less rate - both because of the slower rate of change in volume, and because the initial pressure is lower.

That would, I think, make it more compliant on low-amplitude, high-frequency bumps, which is a win.

You'd lose a little damping sensitivity, because dampers like travel to generate oil flow and thus damping... but these dampers don't strike me as being super sophisticated. Shimstack and bleed, I would think.

The only possible real-world downside I could see is that the softer spring rate and flatter rate ramp might allow more movement with regards to pedaling forces. I know from watching my bike that the rear suspension bobs a little in reaction to pedaling. I totally can't FEEL it - the bike feels like a slightly mushy hardtail, and climbing is 1000% better than my hardtail was - but if I watch the shock, I can see it happening. So maybe the longer travel position makes this worse?

Or maybe not - maybe that was extension die to anti-squat designed into the suspension as a chain torque reaction force....

Some of my race car suspension stuff carries over, but not all of it...

Is there a good analysis of the FSR design around somewhere?

DG