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Offline Kris

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Re: Changing Fork Oil without Special Tools?
« Reply #40 on: February 13, 2018, 03:54:22 AM »
*Originally Posted by Harsh [+]
I hate to rain on your parade, but adjusting the height of the nut did absolutely nothing to the compression or rebound damping.  All it did was maybe change the preload of the spring.  However, if you feel the bike rides better then the below is a moot point, but it is important to understand how forks work so we don't spread misinformation.

The roadie forks use what's called a damping-rod fork.  In which the damping action comes solely from oil being pushed around inside the fork and through sets of small holes.  The big problem with a damping-rod fork is that it can be soft and underdamped during low-speed movement but suddenly turn harsh over the small stuff.  This is because oil forced through a fixed-size hole offers resistance related to its velocity.  So when the oil is barely moving, there's little resistance so it feels soft.  However, when you try to force it quickly through the small holes the resistance goes way up and it feels harsh.

I don't really understand how this shock works, so thank you for that explanation! However, taking out the 1.5mm showing made a huge difference. assuming that the spring preload was indeed increased by 1.5mm, do you think one would even notice it?  people usually put a couple inches spacers to make the spring harder.

In my Versys, there is damping adjuster on the top. you turn it clockwise to increase damping.  I assume that the screw is connected to the damping rod, the same one that is fixed in the Tiger?

Offline AvgBear

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Re: Changing Fork Oil without Special Tools?
« Reply #41 on: February 13, 2018, 04:22:22 AM »
*Originally Posted by Kris [+]
people usually put a couple inches spacers to make the spring harder.
Adding a couple inches of spacers will not result in a stronger spring -- only the same spring with a couple inches of pre-load.
If, instead, the spring was shortened a couple inches (hacksaw-off a couple inches) and, then, a couple inches of spacers added -- well, then, you'd have a stronger spring.
I've ridden all-around the United States and parts of Arkansas.

Offline Kris

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Re: Changing Fork Oil without Special Tools?
« Reply #42 on: February 13, 2018, 05:35:53 AM »
*Originally Posted by AvgBear [+]
Adding a couple inches of spacers will not result in a stronger spring -- only the same spring with a couple inches of pre-load.
If, instead, the spring was shortened a couple inches (hacksaw-off a couple inches) and, then, a couple inches of spacers added -- well, then, you'd have a stronger spring.

this what they say, increasing preload does not increase spring rate.  but based on my experiments with Versys, with less preload the bike was front-diving, so I have some doubts in this theory.

but the change I experienced in Tiger could not have anything to do with spring preload.  it must have been the change in damping.   

Offline Harsh

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Re: Changing Fork Oil without Special Tools?
« Reply #43 on: February 13, 2018, 12:52:45 PM »
*Originally Posted by Kris [+]
I don't really understand how this shock works, so thank you for that explanation! However, taking out the 1.5mm showing made a huge difference. assuming that the spring preload was indeed increased by 1.5mm, do you think one would even notice it?  people usually put a couple inches spacers to make the spring harder.

In my Versys, there is damping adjuster on the top. you turn it clockwise to increase damping.  I assume that the screw is connected to the damping rod, the same one that is fixed in the Tiger?


When dealing with preload you can go down the rabbit hole of spring rates which can get a bit tricky to explain.  AvgBear is correct, you aren't making the spring any harder by adding more preload.  Some riders intuitively feel that adding preload can be used to stiffen or soften the spring, but that isn't really the way it works. The suspension may feel stiffer when preload is increased, but thats because adding preload compresses the spring, so it takes more pressure to move the suspension any further. I would like to say that adjusting preload simply determines the motorcycles ride height or sag, but that wouldn't absolutely be 100% true either because of spring rates.  However, for the average rider I would say that is correct.  We aren't talking about a track bike here so to a large degree spring rates can go out the window.  The below article goes into it a whole lot better than I can.  It can get a bit techy, but is a good read none the less.

https://www.sportrider.com/technicalities-spring-rate-and-preload#page-5


You absolutely did not change the damping in the Tiger when you changed how much thread was showing on the damper rod.  It is a physical impossibility.  On your Versys, based on your description I presume the forks are a cartridge type fork.  Essentially, turning the adjuster screw changes an internal valve which changes how the fork oil will pass through it which changes how the forks react.

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Offline Kris

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Re: Changing Fork Oil without Special Tools?
« Reply #44 on: February 13, 2018, 01:17:29 PM »
*Originally Posted by Harsh [+]

When dealing with preload you can go down the rabbit hole of spring rates which can get a bit tricky to explain.  AvgBear is correct, you aren't making the spring any harder by adding more preload.  Some riders intuitively feel that adding preload can be used to stiffen or soften the spring, but that isn't really the way it works. The suspension may feel stiffer when preload is increased, but thats because adding preload compresses the spring, so it takes more pressure to move the suspension any further. I would like to say that adjusting preload simply determines the motorcycles ride height or sag, but that wouldn't absolutely be 100% true either because of spring rates.  However, for the average rider I would say that is correct.  We aren't talking about a track bike here so to a large degree spring rates can go out the window.  The below article goes into it a whole lot better than I can.  It can get a bit techy, but is a good read none the less.

https://www.sportrider.com/technicalities-spring-rate-and-preload#page-5


You absolutely did not change the damping in the Tiger when you changed how much thread was showing on the damper rod.  It is a physical impossibility.  On your Versys, based on your description I presume the forks are a cartridge type fork.  Essentially, turning the adjuster screw changes an internal valve which changes how the fork oil will pass through it which changes how the forks react.

Harsh, I have a bit hard time to get this suspension mystery.  I read the Race's Tech Suspension Bible and still, some things are not clear to me.  Ok, so let me ask you the question - if I did not change the spring rate or damping by changing how much thread is showing in the damper rod, what the heck did I change to make such a big change?

Offline Harsh

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Re: Changing Fork Oil without Special Tools?
« Reply #45 on: February 13, 2018, 02:00:15 PM »
I believe all you changed was the preload.  You pulled down on the tube (the grey one with the two holes at the top which has the disc with a cut out in in it sitting on top of the tube)(in the parts fiche they are referred to as the spring collar and spring seat stopper) to reveal the lock nut.  Moving the lock nut to reveal more or less threads will have an effect on how much pressure is put on the spring seat stopper and spring collar.  The spring collar sits directly on top of the spring.  So changing how many threads are showing will directly change the preload of the spring.

I will add that new fork oil certainly helps and can change the way the forks feel.  Use a thinner oil and it will flow easier through the orifices.  Use a thicker oil and it doesn't flow as easy through the orifices.  A thicker oil can make the forks feel like there is more compression and rebound damping because it is more restrictive.  Changing the oil weight is an old school trick to change how forks feel when there are no rebound or compression damping adjustments available on the fork, like the Tiger.  On a side note though, not all fork oils are the same weight regardless of what they say on the side of the bottle.  Maxima 10wt is not the same as Ohlins 10wt.

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Offline Kris

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Re: Changing Fork Oil without Special Tools?
« Reply #46 on: February 13, 2018, 03:01:46 PM »
*Originally Posted by Harsh [+]
I believe all you changed was the preload.  You pulled down on the tube (the grey one with the two holes at the top which has the disc with a cut out in in it sitting on top of the tube)(in the parts fiche they are referred to as the spring collar and spring seat stopper) to reveal the lock nut.  Moving the lock nut to reveal more or less threads will have an effect on how much pressure is put on the spring seat stopper and spring collar.  The spring collar sits directly on top of the spring.  So changing how many threads are showing will directly change the preload of the spring.

I will add that new fork oil certainly helps and can change the way the forks feel.  Use a thinner oil and it will flow easier through the orifices.  Use a thicker oil and it doesn't flow as easy through the orifices.  A thicker oil can make the forks feel like there is more compression and rebound damping because it is more restrictive.  Changing the oil weight is an old school trick to change how forks feel when there are no rebound or compression damping adjustments available on the fork, like the Tiger.  On a side note though, not all fork oils are the same weight regardless of what they say on the side of the bottle.  Maxima 10wt is not the same as Ohlins 10wt.



I used the same oil with both 12mm and with 10.5mm showing, 10W Motul, which has more or less the same viscosity as the stock one.  So ok, if the 1.5mm difference, seemingly, changes the spring preload so much - isn't it in contradiction to what AvgBear said that adding the spacer (preloading the spring) does not have the effect on spring's stiffness/softness?   

Offline Harsh

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Re: Changing Fork Oil without Special Tools?
« Reply #47 on: February 13, 2018, 03:39:43 PM »
I only brought up the oil because it is a way to simulate a difference in damping.  I didn't mean to imply that you changed oil weight when you changed the depth of the lock nut.

No AvgBear is still correct.  Just because you change the pressure (preload) exerted on a spring that does not change the physical properties of the spring.  Whether the spring is compressed or in a completely free state it will have the same spring rate.  It will still have the same diameter, same number of coils, etc. 

So lets say you have a 1.0kg spring.  When you compress it, the spring still has a spring rate of 1.0kg.  The spring rate doesn't magically jump to 1.5kg's just because you compress it.  Yes, the further you try to compress it the harder it will get, but you are not changing the spring rate.
Read (or re-read) the article I posted they do a pretty good job at explaining how the force applied to a spring works.

On a fork that has adjustment capabilities for preload externally, one turn of the preload knob can have a fairly dramatic difference.  For the sake of simplicity of this discussion, that one turn of the knob may be equal to 1 turn of the lock nut.  Which in the grand scheme of things isn't that much and may be equal to the 1.5mm difference (12mm to 10.5mm) you had.  On my track bike I set the preload knob in the middle of its range when I assemble the forks.  That gives me 4 complete turns of adjustment in either direction for a total of 8 turns.  Not that much, yet the difference in 1 turn can be dramatic.
« Last Edit: February 13, 2018, 03:49:08 PM by Harsh »
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Offline Kris

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Re: Changing Fork Oil without Special Tools?
« Reply #48 on: February 13, 2018, 04:34:25 PM »
*Originally Posted by Harsh [+]
I only brought up the oil because it is a way to simulate a difference in damping.  I didn't mean to imply that you changed oil weight when you changed the depth of the lock nut.

No AvgBear is still correct.  Just because you change the pressure (preload) exerted on a spring that does not change the physical properties of the spring.  Whether the spring is compressed or in a completely free state it will have the same spring rate.  It will still have the same diameter, same number of coils, etc. 

So lets say you have a 1.0kg spring.  When you compress it, the spring still has a spring rate of 1.0kg.  The spring rate doesn't magically jump to 1.5kg's just because you compress it.  Yes, the further you try to compress it the harder it will get, but you are not changing the spring rate.
Read (or re-read) the article I posted they do a pretty good job at explaining how the force applied to a spring works.

On a fork that has adjustment capabilities for preload externally, one turn of the preload knob can have a fairly dramatic difference.  For the sake of simplicity of this discussion, that one turn of the knob may be equal to 1 turn of the lock nut.  Which in the grand scheme of things isn't that much and may be equal to the 1.5mm difference (12mm to 10.5mm) you had.  On my track bike I set the preload knob in the middle of its range when I assemble the forks.  That gives me 4 complete turns of adjustment in either direction for a total of 8 turns.  Not that much, yet the difference in 1 turn can be dramatic.

thank you for clarifying it for me.  however, the point of contention is this, quote, 'it is a misconception that changing the preload affects the hardness/softness of the bike Because the spring rate does not change, all you change is the sag/hight of the bike'.  Still, ok, even though the spring rate does not change with more preload, the higher/lower spring preload DOES change the subjective feeling of stiffness/softness of suspension, which is what matters for an average rider.

Offline Harsh

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Re: Changing Fork Oil without Special Tools?
« Reply #49 on: February 13, 2018, 04:56:03 PM »
Not sure what else to tell you, but changing the preload has never made any motorcycle I have ever ridden feel stiffer or softer when riding.  All it has ever done for me was to set the sag/height of the suspension so that it operates in its optimum environment (and maybe tell me if the springs were too hard/soft for my weight).  Suspension feel is a subjective thing, so if you feel that it rides/feels better with more or less preload then that is what matters to you.
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