How and why do I set sag on my suspension?

[stangmx13]

Sag is the amount bike and therefore a spring compresses when a force is applied. Since it's impossible to apply a force at the wheel
like in actual road going, it is done by pressing down on the bike.

To set the sag, a preload adjuster is used to apply a static force to the spring by compressing it.

Preloading a spring controls how much force is needed before the spring moves and also how much the spring moves. Also adding preload extends the shock or fork adding ride height.

Preload does not effect spring rate. This meaning once the spring starts moving, it will move at its spring rate.

Dampening controls the force being put into and coming out of the spring.

What wasn't asked was......setting sag for what type of riding.......street, touring, dual sport, dirt, racing and a few others.

And static setting on a bike are just ball park. What the bike does under motion is where the real magic happens. In use, the static settings may need to be changed to further improve the handling.

And remember.....in this valley.......there is no one perfect street setup. Impossible to do.

That's one question I ask when someone when I hear complaints. What road. The perfect, fast, setup for 84 will not be the perfect, fast setup for page mill.

not just any force. the common terminology is that sag == static or total sag. so the sag force is the weight of the bike and the rider.

preload only extends the fork/shock in the case of long soft topout springs. components w/ short stiff topout springs or ones without topout springs do not change their total length when adding preload. preload does affect ride-height which is position, not length.

dampening isnt anything :laughing. damping affects how FAST the spring can move. it may or may not affect how far the suspension moves. it really depends on how long the force input takes. with bumps, it might. with weight forces, braking, or throttle inputs, it prob wont.

edited the last paragraph cuz of an error

 

[stangmx13]

(2) working the suspension in the best part of the damping stroke.

Ideally you want the suspension to be working some where in the mid stroke of it's travel, neither bottoming or topping out.

...

Then there is damping, if your suspension is either topped or near bottomed out you will have only a small amount of oil to force through the damping circuit in one direction or the other.
The damping circuit absorbs the energy of the spring as it compresses or as it decompresses (rebound).

damping force is NOT dependent on position. so it doesnt matter where in the stroke the suspension rides. the amount of oil available to pass through the damping orifices is of no concern unless someone assembled the components incorrectly. there will always be enough oil to provide damping at all suspension positions.

on the race track, the forks spend A LOT of time at the bottom and the top, prob half the entire lap. there is no ideal range of stroke for the suspension to work and ppl that tune to keep a rider out of the bottom third for example are just limiting their options. a good racer is going to use all the stroke and can do so effectively.

 

[dtrides]

damping force is NOT dependent on position. so it doesnt matter where in the stroke the suspension rides. the amount of oil available to pass through the damping orifices is of no concern unless someone assembled the components incorrectly. there will always be enough oil to provide damping at all suspension positions.

on the race track, the forks spend A LOT of time at the bottom and the top, prob half the entire lap. there is no ideal range of stroke for the suspension to work and ppl that tune to keep a rider out of the bottom third for example are just limiting their options. a good racer is going to use all the stroke and can do so effectively.

You are correct in that oil forced through a hole or a shim stack would be the same anywhere in the stroke. But there are many variables. Shim stacks can be velocity dependent which I believe could be different if you only have 1/4 inch of stroke travel vs 2" of stroke travel. Would you activate the complete shim stack in as little as 1/4 " ? And there can be bypass valving that is designed for big hits , how much travel before you see them kick in? I don't know these answers.
And yes , there are top out springs that can really change how to think about set up. BPF forks for example, have a large top out spring that must be considered when setting sag.
I also understand that how one sets suspension on the race track is different than on the road or maybe a rough track.
Nor am I recommending a person keep there suspension out of the bottom third of there travel. I also believe a well set up suspension uses the full travel.
However , I do believe if the suspension spends too much of the time topped or bottomed (mainly talking road riding here) it is not ideal as it can't do its main job which is to keep the tire on the road and chassis stable.
DT

 

[EastBayDave]

Holeshot, that sag is a natural progression as you age. You have to get used to it, and learn to accept it.

Yep; somethings you also have to worry about when you get old:
Is it a fart or a surprise? (quit taking chances.) :rolleyes :fart :green
Your nuts drag t/dirt (watch out f/slamming commode seats!) :wow
Your not flexible enough to drag knee; hurts too much anyway. :x
You can't dice it up in race anymo; 4 abreast no longer an option. :cry

Most of all: No more bouncing off rev limiter w/front in air/sliding rear, while still leaned over/basing fairings in a ultra-tight race on last lap.:thumbdown
But if you still riding, your still happy! :thumbup :teeth :ride

(sigh)....:afm199 :thumbup

 

[EastBayDave]

None of my previous bikes had any really useful preload or any dampening adjustment. When I bought this bike I road for a few weeks with out making changes as I sorted through a few things. Once I adjusted the sag and dampening it was like riding a different bike. The handling improvement was unbelievable.

Just amazing isn't it?
Everyone taking up riding should try it (please.) :thumbup

 

[stangmx13]

You are correct in that oil forced through a hole or a shim stack would be the same anywhere in the stroke. But there are many variables. Shim stacks can be velocity dependent which I believe could be different if you only have 1/4 inch of stroke travel vs 2" of stroke travel. Would you activate the complete shim stack in as little as 1/4 " ? And there can be bypass valving that is designed for big hits , how much travel before you see them kick in? I don't know these answers.
And yes , there are top out springs that can really change how to think about set up. BPF forks for example, have a large top out spring that must be considered when setting sag.
I also understand that how one sets suspension on the race track is different than on the road or maybe a rough track.
Nor am I recommending a person keep there suspension out of the bottom third of there travel. I also believe a well set up suspension uses the full travel.
However , I do believe if the suspension spends too much of the time topped or bottomed (mainly talking road riding here) it is not ideal as it can't do its main job which is to keep the tire on the road and chassis stable.
DT

u are still misunderstanding about damping. uve got some of it backwards actually.

damping is ALWAYS velocity dependent. it does not matter one bit where you are in the stroke for that. if a certain velocity is attained, u get that damping. motorcycle suspension does not have position-dependent bypass valving like a 4x4 truck.

suspension accelerations can be huge which will produce large velocities in short distances. hitting a pothole (a square edge bump) introduces suspension velocity very very quickly. but producing that velocity while already 1/4" from bottom is not worth talking about since u are going to crash :laughing.

shim stacks "activating" is a weird term that i dont think u understand. most stacks are not preloaded, so they are open some for all velocities. on top of that, you get LESS damping the more they open. shim stacks produce linear damping curves by reducing the progressive damping curves produced by orifice damping. a bit hit will open the stack and allow the suspension to move. they dont add damping to prevent u from bottoming. because of that, if u dont have much travel left, u dont want the stack to open.

 

[tzrider]

damping affects how FAST the spring can move. it generally doesnt change how far it moves.

I get what you're saying, though damping can affect how far the suspension moves in one respect: If you hit a bump that could displace your suspension 2" but the damping rate only allows one inch of movement by the time you've cleared the bump, the suspension will not travel the full two inches since the input force is already gone.

 

[stangmx13]

I get what you're saying, though damping can affect how far the suspension moves in one respect: If you hit a bump that could displace your suspension 2" but the damping rate only allows one inch of movement by the time you've cleared the bump, the suspension will not travel the full two inches since the input force is already gone.

ya, i typed that too fast. thnx for the catch. edited.

there are plenty of situations where damping will affect how far the suspension moves. there are also plenty of situations where damping has no effect on far the suspension moves.

 

[tzrider]

ya, i typed that too fast. thnx for the catch. edited.

I like your edit. Really clarified your point.

 

[Shaggy]

:laughing Great discussion!

 

[stangmx13]

:laughing

 

[Holeshot]

preload does affect ride-height which is position, not length.

Correct, and changing preload effectively changes static weight distribution.

 

[dtrides]

Stangmx13, sorry I am not able to articulate more accurately.
I do see and agree with most of your points.

So getting back to setting sag, for me I want to have the bike sprung for my weight , sag set so I am not topped out , which will allow the suspension to extend in to a depression or on the downhill side of a rise just a bit. Like wise, being high enough in the stroke so as to not bottom under normal conditions so when I hit pavement heave mid corner with the front suspension loaded (especially a down hill corner) that way there is just a bit of travel left to absorb some of that force keeping my tires on the pavement.
And I am talking street, not track.
Obviously there are soooo many other factors that are intertwined. Like as you mentioned how preload changes ride hight which effects the geometry, CG, etc.
DT