Given both have seals why coil plusher air?

ccm said:

Since both coil and air forks/shocks have wipers and seals, why are coil springs reportedly plusher than air springs?
Such as reports that Marzocchi Marathon XC is better than Marathon SL? Both forks should have equal seals and wipers.

Does the air negative spring provide more assistance for the shaft to move when the fork/shock is topped out? and become less effective as the fork/shock is compressed? Or does a more linear spring rate allow for more travel and therefore a plusher feel? (air can be made more linear with larger volume anyway and coil springs can be made to be variable weight with various windings and variable diameter, so this is likely not the reason unless the reported spring rates only apply once the shaft is moving).

Even more complicated is the matter than all forks/shocks ride on two big air springs (the tires). So in one case you have a coil sping stacked on top of an air spring, and the other you have two air springs in series (is there some conflict between these two air springs that binds/limits shaft movement of the shock?). Do the coil and tire both start reacting at the same time to input, whereas the tire has to deform to a certain point before the air shock begins to move?

Click to expand...

Air pressured seals are tighter, increase stiction. And spring rate of coil is linear, vs. progressive rate air chamber springs.

I converted an earlier Marzocchi air fork (x-fly 100) to coil and the difference in ride was noticably more buttery and with less wallow.

I attribute the more buttery ride mainly to less seal friction, although that shock just had firm topout negative springs which didn't reduce the spring preload effect of air. Double air still has much more friction at the seals. And the less wallow of my converted air to coil, because of the more rapid spring rampup in mid travel (just below sag).

And the tires matter a lot too. Lower friction coil makes a smoother transition from the undamped air spring of tires. If changing to bigger volume tire, lighten up the shock and fork damping and reset only as firm as needed to match your conditions.

The newer high end slider anodizing or ceramic finishes are much less sticky as earlier models of air. The difference in stickiness is becoming very close between air and coil. And to some degree the new firmer speed-sensitive damping compensates for the deeper rampup of air spring action. And many bikes are now designed with rapidly digressive rising or falling rate shock linkage leverage for better adapting air rear shock' rising rate spring action; so coil can feel too firm, especially when combined with platform valving.

It's getting close to the point where the only advantages of coil is the greater reliability and lack of frequent air spring pressure checking.

It's easier to sell air shocked bikes out the door to anyone. Coil has to be over sprung for lighter riders to be able to sell to heavier riders of the same frame fit.

In the long run coil is more fine tunable, always for forks, and usually for the rear if the rear shock linkage is not very digressive in leverage rate. But it takes longer to get sorted for each rider, often costing a few somewhat costly spring changes.

F1, MotoGP, MotoX, etc all use coil springs for suspension. They would use air springs if there was a performance advantage. F1 and some MotoGP bikes do use air for valve springs, titanium coil is too heavy to react fast enough for the revs used now.

- ray