Rear Suspension Preload Setting

[Edmund Kean]

Sorry to ask what perhaps to some is a basic question, but from reading a thread on the other ST1300 forum I’m left a little puzzled.

In an attempt to achieve ‘correct’ sag whilst I’m on the bike, I did the following.

Put the bike on it’s centre stand.

Removed the right pannier.

Taped a piece of string to the axle bolt of the drive shaft.

Put a piece of masking tape on the painted plastic panel vertically above the axle bolt at the drive shaft.

Put a level line on the masking tape.

Offered the string taughtly and marked a point on the string corresponding to the marker on the masking tape.

Measured and placed two marks lower down the string. One mark at 30mm and the other at 36mm from the first and original mark.

Put my gear on and a 2.5 kg weight in a rucksack on my back. This to restore the weight lost from the removed pannier.

Sat on the bike and with a pole and a wall, balanced all my weight on the bike.

My wife then offered up the string and bingo, the 30mm deflection marker was lining up with the mark on the masking tape.

Now I didn’t expect this, as all I keep reading is how undersprung the shock is. I’m about 195 pounds fully geared. The shock preload is just about in the middle of its range of available clicks.

The bike is currently very low on fuel. So I suppose another 26 kilos could be attributed to the equation in a manner.

Have I done something wrong?

 

[CYYJ]

Hi Edmund:

I don't know enough about suspension setup to answer your question, but I can offer a couple of thoughts that might be helpful:

1) The preload adjuster on the ST 1300 rear shock absorber is notorious for "drying out". It works by pressing hydraulic fluid into the shock absorber, thus applying preload. It is very common for this hydraulic fluid to disappear (I have no idea where it goes), resulting in a loss of ability to apply preload. You can verify whether there is fluid in the preload system by backing the preload adjuster knob out all the way, then starting to turn it inwards. If you do not feel the onset of significant resistance after about 3 or 4 clicks, the preload adjuster needs to be serviced (have oil added). There is a lengthy discussion about how to service it here: ST1300 - Pre-load Fluid Replacement.

2) I doubt that the quantity of fuel in the tank would have a material effect on rear shock performance. The tank holds 7.7 US gallons, fuel weighs about 6 pounds per US gallon, hence a full load of fuel is about 42 pounds. If half that weight is supported by the rear tire, that's only a 20 pound difference.

Michael

 

[dduelin]

I don't think you did anything wrong, with the stock shock's preloader working correctly (making resistance from the first turn or two) it's no problem to set 25-35 mm rider sag with your weight. However, this is only half the picture. A too-soft spring with a powerful enough preloader will set rider sag correctly but to complete the analysis now you should measure sag with your weight off the bike. If there is 5-10 mm of free sag the spring is in the ball park for your riding weight. If there is less than 5 mm without your weight on it that indicates that your weight blows right through the preload and the spring is too soft for you.

 

[Edmund Kean]

I don't think you did anything wrong, with the stock shock's preloader working correctly (making resistance from the first turn or two) it's no problem to set 25-35 mm rider sag with your weight. However, this is only half the picture. A too-soft spring with a powerful enough preloader will set rider sag correctly but to complete the analysis now you should measure sag with your weight off the bike. If there is 5-10 mm of free sag the spring is in the ball park for your riding weight. If there is less than 5 mm without your weight on it that indicates that your weight blows right through the preload and the spring is too soft for you.

Thanks Dave, I wouldn't have known to perform this complete check of sag. So having just done it, I can report the free sag was showing at about 7-8mm (I used quite a broad tipped marker pen). Considering I have very little fuel, I can only presume the measurement would increase slightly towards 10mm.

So it appears I'm lucky to have a spring which is more or less suitable, unless of course I were to carry a pillion.

Just curious Dave, you mentioned rider sag between 25-35mm. On the other forum, I read a range of 30-36mm. Now, the reason I performed this check is because a few years back, I owned a ST1300 and I used to be able to easily U-turn in the pushing style. Unless it's my confidence at the moment but the bike (or me?) doesn't feel so willing to be pushed. A few years back when I rode with a pillion quite a lot, I used to keep the preload wound right up and wouldn't touch it when solo or practicing in car parks. So, in attempt to get that feel I thought about the preload to maybe sharpen or speed up the steering.

Any thoughts...

 

[Larry Fine]

If I may, when I bought my '01 ST1100, I noticed it resisted leaning with counter-steering effort, especially as compared to my '96 Nighthawk 750. After riding it for several weeks, as I got used to it, it didn't improve. As I am heavier that the previous owner, I decided to adjust the rear suspension to raise the back of the bike. I remember reading about steering geometry, that the more vertical the forks, the quicker the steering.

I turned the rings on the Progressive rear shock about a half-inch higher on the shock itself, which raised the rear of the bike, but I'm not sure how far the bike itself raised. I can tell you that the steering improvement was immediately noticeable. The steering was neutral and easy to control, and provided confidence and predictability. It's easier to make small adjustments of applied force when you're not having to apply great force.

 

[Edmund Kean]

If I may, when I bought my '01 ST1100, I noticed it resisted leaning with counter-steering effort, especially as compared to my '96 Nighthawk 750. After riding it for several weeks, as I got used to it, it didn't improve. As I am heavier that the previous owner, I decided to adjust the rear suspension to raise the back of the bike. I remember reading about steering geometry, that the more vertical the forks, the quicker the steering.

I turned the rings on the Progressive rear shock about a half-inch higher on the shock itself, which raised the rear of the bike, but I'm not sure how far the bike itself raised. I can tell you that the steering improvement was immediately noticeable. The steering was neutral and easy to control, and provided confidence and predictability. It's easier to make small adjustments of applied force when you're not having to apply great force.

Thanks for your input.

 

[dduelin]

				Thanks Dave, I wouldn't have known to perform this complete check of sag. So having just done it, I can report the free sag was showing at about 7-8mm (I used quite a broad tipped marker pen). Considering I have very little fuel, I can only presume the measurement would increase slightly towards 10mm. So it appears I'm lucky to have a spring which is more or less suitable, unless of course I were to carry a pillion. Just curious Dave, you mentioned rider sag between 25-35mm. On the other forum, I read a range of 30-36mm. Now, the reason I performed this check is because a few years back, I owned a ST1300 and I used to be able to easily U-turn in the pushing style. Unless it's my confidence at the moment but the bike (or me?) doesn't feel so willing to be pushed. A few years back when I rode with a pillion quite a lot, I used to keep the preload wound right up and wouldn't touch it when solo or practicing in car parks. So, in attempt to get that feel I thought about the preload to maybe sharpen or speed up the steering. Any thoughts... Edmund, I wasn't that clear in that post. A better turn of phrase could have been "the preloader can easily produce as little as 25 mm of sag" (at least with my scrawny body). I agree a range of sag could be said to be aproximately 30 to 40 mm or 25 to 33% of travel. These are suggestions and individual likes or dislikes impact what is "best". As Larry Fine pointed out in the post above and you allude to, rear sag can significantly change steering geometry. In my case, working on the forks alone I raised the fork ride height 11 mm, significantly slowing steering inputs and allowing the bike to run wide on corner exits, and I was able to recover 5 mm of that by sliding the tubes up in the clamps. To help restore the light, neutral steering characteristics I preferred to set rear sag to the lower end of the 25-33% range. IIRC 7 - 9 clicks of preload set my rear sag to low thirties, 12-14 clicks to high twenties sag.

 

[Edmund Kean]

				Edmund, I wasn't that clear in that post. A better turn of phrase could have been "the preloader can easily produce as little as 25 mm of sag" (at least with my scrawny body). I agree a range of sag could be said to be aproximately 30 to 40 mm or 25 to 33% of travel. These are suggestions and individual likes or dislikes impact what is "best". As Larry Fine pointed out in the post above and you allude to, rear sag can significantly change steering geometry. In my case, working on the forks alone I raised the fork ride height 11 mm, significantly slowing steering inputs and allowing the bike to run wide on corner exits, and I was able to recover 5 mm of that by sliding the tubes up in the clamps. To help restore the light, neutral steering characteristics I preferred to set rear sag to the lower end of the 25-33% range. IIRC 7 - 9 clicks of preload set my rear sag to low thirties, 12-14 clicks to high twenties sag.

Thanks for all the input, I’m fairly squared with it all now.