ST1300 - Unstable when riding behind a semi truck?

[MidLife]

Feel the difference?

I'm sure I would...

Well...first you said preload wouldn't affect rebound and now....you are sure you would feel it if you were trying? That was the point of you trying what @ASPC suggested.

 

[Larry Fine]

Well...first you said preload wouldn't affect rebound and now....you are sure you would feel it if you were trying? That was the point of you trying what @ASPC suggested.

I'm sure I would feel the difference. I have no idea what part, if any, would be due to damping differences.

As I said, springs and shocks are very different mechanisms. I have never adjusted the damping on a bike.

 

[Willsmotorcycle]

If the bike "po-go sticks", add some rebound damping.

It is "packs", take some off.

Thank you, this is the simplicity I have been looking for.

 

[Larry Fine]

"While we did not measure the spring stiffness directly, we determined the compression of the spring at each preload setting: 5 mm for the smooth preload, 7.5 mm for the medium preload, and 9.7 mm for the strong preload."

I still don't understand what actually made the spring shorten instead of raising the bike.

 

[Larry Fine]

If you are not used to digesting this kind of material, have a look at Dave Moss (a well-known professional tuner) adjusting preload and see how his adjustment to the preload affects how the suspension rebounds. Look first at 3:30. And he does it again at 1:40.

I hear him saying it, but I don't know what he's adjusting or seeing/feeling.

If what he does here is not clear to you, please let me know. I would also gladly give you a call to point out exactly what to look at while you watch, if you are really interested, just send a PM.

Done.

 

[Dmackeld]

When I drive without a top case, there is hardly any instability behind a truck. I drive with Dunlop roadsmart 4, I haven't driven a Metzler Z8 yet. I have a Wilbers chassis with Nivomat and shorter fork springs (15mm), Mr. Wilbers said that a Pan ST1300 has to go down at the front.

 

[ASPC]

When I drive without a top case, there is hardly any instability behind a truck. I drive with Dunlop roadsmart 4, I haven't driven a Metzler Z8 yet. I have a Wilbers chassis with Nivomat and shorter fork springs (15mm), Mr. Wilbers said that a Pan ST1300 has to go down at the front.

At what speeds?

 

[jfheath]

When I drive without a top case, there is hardly any instability behind a truck.

When you ride solo, the wind eddies - swirls around behind your back. It is what happens when an object (you) gets in the way of a flow of wind or water. It often tends to swirl in behind your back on one side, and then does the same on the other - alternating left, right, left.

This is of little consequence when there is nothing behind you, but leave a gap and put another obstacle in the way - the air is not going to hit it front on - it will hit it alternately from each side. That is your top box. Put a pillion between you and the top box and the bike handles smoothly. Any side-slapping isn't going to affect you - only the rider behind.

If it concerns you - as it did me when I got my first ST1100, after a very long layoff after the kids no longer fitted into the sidecar - then remove the top box, make sure the rear preload is not set too high and go out in breezes and see what it feels like then. Get used to it - train your brain not to grip the bars with rigid arms. On the straights, curl your hands around the grips so that the bars cannot escape, but leave them slack. Get used to that and then put the top box on again. If it is a Honda box, then make sure that it can move laterally - the mount is designed to allow a centimeter or so of lateral movement. Enough to yield against the wind rather than affecting the back of the bike.

Or fit a pillion - which is what we did. So much nicer to ride in those early days with two of us on the saddle, and a top box behind.

Now it doesn't bother me nearly as much with a pillion or not.

 

[MidLife]

I still don't understand what actually made the spring shorten instead of raising the bike.

Oh no! You went through that before and had it all figured out. Let's hope you can get back to that prior frame of mind!

It is not an either/or condition: Both are happening, the "installed length" of the spring gets shorter by the preload amount ("installed length" is the length of the spring you could measure if you had the shock by itself in your hands, with the shock fully extended) AND the bike will sit a tad higher when the shock with installed preloaded/shorter spring is mounted on the bike.


@jfheath schematic is best for illustration,




In Fig 2, you established there is too much sag (Too Low) and you'd like to correct that, you want to sit higher.

In Fig 3, you have the shock fully extended. Imagine it is sitting like that on the bench (But it is the same with the bike on the center stand and shock fully extended, wheel off the floor). But for illustration purposes, think about it being on the bench in front of you.

In Fig 4, you've added preload and the installed length of the spring is now shorter by the preload amount (Imagine it is still on the bench). Total length of the shock itself is still the same, it cannot extend further. The spring is just pre-compressed/preloaded a bit more on the shock and is now shorter.

In Fig 5, you are sitting on the bike with the shock with the shorter/preloaded/precompressed "installed length" AND you are sitting higher (Compressed length of the spring when sitting on it is of course the same as before adding preload, but you are sitting higher).

So you have both, higher sitting position (raised bike) AND shorter preloaded/precompressed "installed length" spring.

Preload is all about this "pre-compression" of the spring on the shock body. That's what is meant by pre-"load".

Thank you to @jfheath for making it so perfectly clear.

 

[MidLife]

I'm sure I would feel the difference. I have no idea what part, if any, would be due to damping differences.

Good you put it in these words: I can see now where you are diverging.

Nobody is pretending that changing preload would affect the damping setting. It does not. The damping setting remains constant as long as you do not touch the adjustment screw. That's for sure.

What changes (DYNAMICALLY) when you change the preload, is the rebounding response/oscillating of the suspension itself (bouncing or packing), which is not the same as changing the damping.

If you keep tightening the preload without changing/adjusting damping at the same time, the rebound behavior will change towards more and more po-go sticking (over-rebounding, bouncing). To prevent the bouncing, damping should be tightened (add damping, counterclockwise) as more preload is added.

If you keep loosening up the preload without changing/adjusting damping) at the same time, the rebound will tend towards starting to pack (under-rebounding), which can be prevented by loosening damping (clockwise) as the preload is loosened up.

As I said above, springs and shocks are two very different mechanisms.

Of course, but although spring and dampener are two different components of the shock absorber, they both affect the rebounding/oscillating behavior of the suspension (but as said, tightening the spring/preloading does not change damping itself, only the oscillation/bouncing response of the suspension). Changing either preload or damping will both alter the rebounding characteristic (or oscillations) of the vehicle (like the tendency to po-go stick/over-rebound, or pack-off/under rebound).

 

[Dmackeld]

At what speeds?

Speed 160km/h

 

[MidLife]

I ordered a Laminar Lip based on this review and several others on the Laminar site. I have yet to ride with it because it's 115 degrees here but am looking forward to reducing this buffeting behind semis as well. I thought maybe I was the only one, or perhaps something was wrong with my ST13.

How long ago did you purchase it? The Lip site seems to be down and not answering eMails and some think they could be out of business?

 

[Larry Fine]

It is not an either/or condition: Both are happening, the "installed length" of the spring gets shorter by the preload amount ("installed length" is the length of the spring you could measure if you had the shock by itself in your hands, with the shock fully extended) AND the bike will sit a tad higher when the shock with installed preloaded/shorter spring is mounted on the bike.

To me, you're contradicting yourself here. Either the spring shortens because the shock is already topped out before adjustment, or the bike height rises because the shock wasn't already topped out before it.

Otherwise, you're comparing two different conditions, one being in-the-hands, the other being mounted on the bike with weight on it. If you stick with one condition, then only one of the two reactions will occur.

Am I correct so far?

 

[Larry Fine]

So you ARE including the shock being topped out in the discussion. Of course the spring gets shorter then.

I only care about what happens under riding conditions, so only figures 2 and 5 matter in the discussion.

Those are the only conditions that occur while the bike is in use. Does damping alter between the two?

 

[Larry Fine]

Nobody is pretending that changing preload would affect the damping setting. It does not. The damping setting remains constant as long as you do not touch the adjustment screw. That's for sure.

Hooray!

What changes (DYNAMICALLY) when you change the preload, is the rebounding response/oscillating of the suspension itself (bouncing or packing), which is not the same as changing the damping.

Are you saying that an adjusted-for-different-weight spring has different damping requirements?

Or rather, that the difference in the weight itself is what requires a different amount of damping?

If you keep tightening the preload without changing/adjusting damping at the same time, the rebound behavior will change towards more and more po-go sticking (over-rebounding, bouncing). To prevent the bouncing, damping should be tightened (add damping, counterclockwise) as more preload is added.

If you keep loosening up the preload without changing/adjusting damping) at the same time, the rebound will tend towards starting to pack (under-rebounding), which can be prevented by loosening damping (clockwise) as the preload is loosened up.

Of course, but although spring and dampener are two different components of the shock absorber, they both affect the rebounding/oscillating behavior of the suspension (but as said, tightening the spring/preloading does not change damping itself, only the oscillation/bouncing response of the suspension). Changing either preload or damping will both alter the rebounding characteristic (or oscillations) of the vehicle (like the tendency to po-go stick/over-rebound, or pack-off/under rebound).

It sounds like everyone should have been saying to remember to adjust damping when you adjust the "preload" instead of implying that it automatically will adjust itself as you do.

 

[Larry Fine]

Now, I do of course get that a spring with more weight will shorten, and that's what the preload adjuster is there for: to compensate for weight in order to maintain a given height under different loads.

The greatest effect of this adjustment I have observed is on steering effort, because it affects steering geometry, i.e, the fork angle; rake, trail, etc., so that's my gauge for finding the best setting.

My '01 came with a Traxxion Dynamics fork mod and a Progressive rear shock/spring, thanks to the P.O. The only adjustment I've made, as I said before, was to compensate for my greater weight.

As far as I know, the '96 I bought this spring (no pun intended) has the original suspension. It sits lower than the '01, and the fork has some stiction, but it handles well with no adjustments by me.

I really wouldn't want to start futzing with whatever damping adjusters either one has without some good guidance. I wouldn't know what to look or feel for, even after watching that track guy's video.

 

[MidLife]

......have a look at Dave Moss (a well-known professional tuner) adjusting preload and see how his adjustment to the preload affects how the suspension rebounds. Look first at 3:30. And he does it again at 1:40.

I hear him saying it, but I don't know what he's adjusting or seeing/feeling.

Both the 3:30 and 1:40 cases are similar.

A racer comes in and, as Moss demonstrates and you can clearly see, he finds out their front shock is bouncing too much, it overshoots its initial position before settling.

One obvious solution would be to tighten up the damping setting to eliminate the bouncing.

But...Dave knows suspension (that's what he does for a living!). He knows that he can also reduce the bouncing by adjusting the preload.

In both cases, the racers had cranked up the preload for no good reason. So all Dave does is remove some of the preload on the front springs (when you see him busy with his screwdriver over the top of the forks, that's what he is doing, removing some of the spring preload).

And once he has adjusted the preload (reduced it), as he demonstrates and you can clearly see, the over-bouncing is gone.

You cannot have a clearer demonstration of preload also affecting bouncing of the suspension, not just damping adjustment.

 

[Larry Fine]

And once he has adjusted the preload (reduced it), as he demonstrates and you can clearly see, the over-bouncing is gone.

You cannot have a clearer demonstration of preload also affecting bouncing of the suspension, not just damping adjustment.

So, do either of my bikes have any of these adjustments, other than the rear spring?

Is it okay to use my front brake while bouncing? I don't have a chock.

 

[jfheath]

It sounds like everyone should have been saying to remember to adjust damping when you adjust the "preload" instead of implying that it automatically will adjust itself as you do.

Yes. Every time I talk about it, I deliberately fail to mention this - as usually once concept at a time can be difficult enough to follow.

Actually - I like @MidLife's explanation of the 5 stages in my diagrams, better than my own. I may (with your permission) quote that in my original explanation. Two ways of describing the same thing are always a good idea.

Adding pre load does not affect the damping. But adding more weight to the bike will. There is more weight and inertia to slow down than there was before, so something to stop it rebounding quickly and then bouncing again is needed - so it might feel as though it has affected the original setting. In fact it hasn't. Its just that it was perfectly ok for the previous weight, but now you have added more, you need a bit more damping to slow it down.

In the same way that a heavy express arriving at the buffers in a terminus isn't going be very impressed with a strip of sorbothene. It will need a tad more than that.

 

[Larry Fine]

Yes. Every time I talk about it, I deliberately fail to mention this - as usually once concept at a time can be difficult enough to follow.

I obviously need to hear it to grasp the concept.

Adding pre load does not affect the damping. But adding more weight to the bike will.

That is SO different than everything I read before.

Even then, it isn't the damping that changes with spring adjustment, it's the bike's response to the existing settings that changes.

Yes?

There is more weight and inertia to slow down than there was before, so something to stop it rebounding quickly and then bouncing again is needed - so it might feel as though it has affected the original setting. In fact it hasn't. Its just that it was perfectly ok for the previous weight, but now you have added more, you need a bit more damping to slow it down.

Got it.