Something that you might need to bear in mind before slapping a coil on your bike is whether the suspension kinematics can cope with the linear nature of a coil. Most frames sold now have a significant chunk of anti-squat designed in so they’ll be ok, not all though.
I think the linear nature of a coil spring is one of the most misunderstood/misquoted things on MTB forums (I’m not saying you misunderstand, but as you mention it, it’s a good talking point).
Some people speak of this linear nature as though on some frames, once you’ve set your sag, if you hit a big bump you’ll blow through your travel instantly; “you need air for the ramp up etc”.
My understanding of a coil spring is that as you try compress it further, the more force is needed. So my 650lb spring, to compress it 1 inch takes 650lb of force, but to compress it another inch takes a further 650lb of force (meaning it takes 1300lb of force to compress my spring 2 inches). This means that the spring does indeed “ramp up”, but in a wholly predictable “linear” way.
I also think it’s this misunderstanding that prompts folk to make statements such as “you can’t use a coil on an Orange”. Because Orange have fairly consistent (flat??) leverage rates/kinematics, the leverage acting upon the spring is consistent through the whole travel meaning ramp up comes from the spring weight/rate, with the speed/suddenness etc. of compression & rebound being controlled by the damping. Indeed, I think it’s the constant leverage rate and consistent linear nature of how a coil compresses that makes coil shocks suit Orange bikes so well.
I’m guessing here that on bikes with funky leverage curves, because coil shocks are linear (consistent) throughout their compression they remove a variable i.e. the S shaped curve as described by Ben above. Which could serve to “flatter” less than optimal suspension designs. Again, just a guess here, but as you can probably tell, I’m a big fan of coil shocks.
