Suspension Damping question

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This past winter, during my bike's layup, I did the usual routine maintenance and also cleaned and replaced the oil in the rear shock's preload adjuster and lightened the damping slightly. I screwed the adjusting screw on the right side of the bike (through the hole in the frame) all the way in and backed it out about 1 1/4 turns.

On my way to the Mansfield RTE (and on the way home) I felt the bike weaving/wobbling when I was cruising at, ahhhhhh, supralegal speeds in the turbulent air behind semi rigs. This only occurred when I was behind, and usually one lane over from the semi, and a few car lengths back. Obviously, this was the most turbulent air from the truck. I did not notice this wobble at all last summer.

Could easing off the dampening have caused this instability?

Today I increased the damping to 1 1/2 turns out from screwed in tight (well, gently tight). I'll see how the bike handles next time I take it out, and continue playing with the adjustment. Unfortunately, a heavy work load may delay biking for a week or two.
 

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Yes it can as the resr ends up being softer and bouncy a bit. A firm setting resists thet and results in a more stable ride. The ST is prone to issues with dirty air around big rigs anyway.
 

dduelin

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Turning the screw out (counter clockwise) from fully turned in decreases damping. Fully clockwise with the screw lightly seated against the stop is the highest amount of damping available. The standard amount to start from is 1 turn CCW from seated full in. Moving from 1 1/4 to 1 1/2 CCW is decreasing damping.

The conventional wisdom is that lots of preload coupled with hard damping helps ST1300 feel better in dirty air or at higher speeds. Try 1 turn or 3/4 turn out from full hard and see if this helps. Too much damping feels harsh on rough pavement but on smooth pavement at speed it may help settle the bike down.

https://www.youtube.com/watch?v=CAhksxRCIik
 

mlheck

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The other questions that needs to be asked is where is your preload set at now versus before. I agree that the rebound damping is most likely the issue, but one must make some note of rear sag before rebuilding the preload adjuster. Counting clicks is a guess at best.
 

Kevin_56

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rear sag before rebuilding the preload adjuster.
I have not ran across a 1300 that does not need fluid added to the preload unit. If you have not done a simple test to see, try this. From where ever you have yours at, start turning it counterclockwise and as soon as there is no longer any resistance, start counting the turns till it stops. If it is more than one turn you are low on fluid. Mine was at 8 turns. Once refilled it is less than 1. I could tell a difference in handling immediately.
 
OP
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Turning the screw out (counter clockwise) from fully turned in decreases damping. Fully clockwise with the screw lightly seated against the stop is the highest amount of damping available. The standard amount to start from is 1 turn CCW from seated full in. Moving from 1 1/4 to 1 1/2 CCW is decreasing damping.

The conventional wisdom is that lots of preload coupled with hard damping helps ST1300 feel better in dirty air or at higher speeds. Try 1 turn or 3/4 turn out from full hard and see if this helps. Too much damping feels harsh on rough pavement but on smooth pavement at speed it may help settle the bike down.
The other questions that needs to be asked is where is your preload set at now versus before. I agree that the rebound damping is most likely the issue, but one must make some note of rear sag before rebuilding the preload adjuster. Counting clicks is a guess at best.
Thank you all. I obviously had the direction to turn to lighten damping backwards in my mind. I'll tighten the screw 1/4 turn from my previous setting before my next ride. The preload adjuster needed maybe 2+ turns before to hit resistance. Now it is less than half that. Before it was set at the owner's manual recommended setting. Now it is half a turn LESS than that.

What kind of sag should I have when setting up the bike? Do I back out the preload to zero, measure the sag, crank the preload to measure the sag, and then back it off to let the bike settle to the half way point? I weigh 150 lbs and usually ride with minimal stuff in the rear bags and top bag. Usually a rain suit, rain gloves, and a tool pouch and compressor, and rags and windshield polish. Figure 10 - 15 lbs max back there (tools mostly).
 

dduelin

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I weigh almost identical to you and also normally carry less than 10 lbs on day rides. Sag is normally measured once with you on the bike ( rider sag )and then again with the rider off the bike (static sag). But we can dispense with that if all you are interested in is general recommendations. The ST is softly sprung and will have generous sag at the recommended 7 clicks even with a 150 lb rider. Of course this is clicks after resistance is felt so if you have 1 or 2 turns of no resistance just account for that. 2 turns play or no resistance + 7 turns = 9 turns from fully soft or fully counterclockwise to the stop.

If the fork is stock it has lots of sag, probably 45-47 mm at a rider weight of 150 lbs. IIRC my stock shock gave about 30-32 mm of rider sag at the recommended setting of 7. For higher speeds in dirty freeway air I'd try using 12-14 clicks of preload to get sag around 24-25 mm. IIRC there are 36 clicks or 18 full turns of preload travel so at 12 to 14 clicks you have plenty left for a passenger or a load of touring gear. It's normal to add a little rebound damping if you increase preload which you already mentioned.
 
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Hi,

Can I ask what I hope is not a stupid question. I have just done the preload adjuster refill and now am not sure what it was set at before as it was nearly empty. Reading you talking about rider weight, and reading lots of other articles on suspension, as a 200lb rider and always carrying 20lb of bits and bobs, it seems I am too heavy for the original shock. Should I therefore simple turn the preload right up and then play with the damping to match that setting? Or have I got the completely wrong idea? If so I would appreciate a signpost to something to put me right. Many thanks.
 

mlheck

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You're not too heavy for the shock, the spring itself, yes. You can crank the preload up to get the right sag, but you will most likely use most of your preload adjustment. To answer your question though, you are on the right track using the stock spring and shock.
 
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