suspension stiction / resistance to movement

[clockworked]

To the physics nerds:
Is stiction at the start of the stroke in air suspension the same independent of spring rate?

Ie: is stiction a relatively larger problem for lighter riders, or does the stiction stay relative to weight for heavier riders?

Do lighter riders find more benefit in initial sensitivity from coil springs than heavier riders?

 

[link1896]

Great question.

Only the bike world calls it stiction. The proper term is breakaway force. Breakaway force is a combination of many things.


Oring crush (how small the grove in the air piston head is relative to the oring dimensions, forcing the orings to crush more on the inside wall of the stanchion and piston rod)
Stanchion wall and piston rod smoothness, smoother = reduced force required to breakaway from the stationary position
Oring material.
Air pressures.

If you have a properly designed dual air system, not solo air BS but real dual air, you balance out the air piston forces, they are opposing each other. You are left with the orings ( piston head oring and negative oring that’s sealing on the piston shaft) crush (can’t be zero, otherwise they won’t seal) that has to be overcome. Higher the air pressures, the higher these forces are.

How this changes for different weight riders I don’t have any measurements. Very good question.

 

[creaky]

Breakaway force is a combination of many things.


Oring crush (how small the grove in the air piston head is relative to the oring dimensions, forcing the orings to crush more on the inside wall of the stanchion and piston rod)
Stanchion wall and piston rod smoothness, smoother = reduced force required to breakaway from the stationary position
Oring material.
Air pressures.

Wouldn’t the lubricant be a factor also ie dry vs superlube 3000 ?

 

[Cleverly]

Is stiction at the start of the stroke in air suspension the same independent of spring rate?

Think of it more like the difference between kinetic and static friction. The force required to move something from a static state is greater than that to keep it in motion. Few good simple Newtonian physics demonstrations of this if you want to dig into it a little more, but IIRC it's frictional co-efficient and the normal force between the two objects/surfaces.

Spring rate should be set to weight, which means the forces should be "relatively" similar even if the exact numbers vary. That being said there's an argument to be made that the higher the pressures the greater the friction, but it also means the greater forces being generated to get them into a state of motion, so "relative" difference shouldn't be all that different unless you stray into extremes.