Rebound adjustment help please

[MidLife]

Oddly enough, no. The shock's pre-load setting does not change the shock's spring compression/extension rate. One would change the rebound setting if 50 or more pounds (22kg) weight (mass) was added or subtracted, though; more for more, less for less.


Marshal

If 50 lbs or more were added, wouldn't you also crank up the preload to maintain nominal sag?

 

[Marshal_Mercer]

If 50 lbs or more were added, wouldn't you also crank up the preload to maintain nominal sag?

On the stock ST's shock, yes.

But the question was about the rebound damping, the only adjustable damping on the stock ST. I would not adjust the damping because of the pre-load adjustment. I would increase it because of the increased mass. Remember: rebound damping is independent of the spring compression (it works on spring extension), so spring pre-load does not enter into the damping question.

The problem here is that as the stock ST's shock spring is too weak for the bike in the first place, so one has to make both adjustments. It seems as though one setting affects the other because of this. It does not. Point in fact: I have an after-market shock with a spring adequately strong (1,300 pounds) for a passenger, a rider, and gear. The sag has been set, both front and rear with this in mind. I do not need to adjust the shock spring's pre-load, even when adding a passenger. I do need to change the compression damping, though: more for more mass, less for less. Not much, mind you, but some.

As the rebound damping was adjusted for the spring rate and passenger + rider + gear mass, the rebound rate generally stays the same. Unless I want to go "bonkers" in the mountains. Then the rebound damping goes up one click. It goes back to the prior setting for freeways.

Hope that this make sense,

Marshal

 

[dduelin]

On the stock ST's shock, yes.

But the question was about the rebound damping, the only adjustable damping on the stock ST. I would not adjust the damping because of the pre-load adjustment. I would increase it because of the increased mass. Remember: rebound damping is independent of the spring compression (it works on spring extension), so spring pre-load does not enter into the damping question.

The problem here is that as the stock ST's shock spring is too weak for the bike in the first place, so one has to make both adjustments. It seems as though one setting affects the other because of this. It does not. Point in fact: I have an after-market shock with a spring adequately strong (1,300 pounds) for a passenger, a rider, and gear. The sag has been set, both front and rear with this in mind. I do not need to adjust the shock spring's pre-load, even when adding a passenger. I do need to change the compression damping, though: more for more mass, less for less. Not much, mind you, but some.

As the rebound damping was adjusted for the spring rate and passenger + rider + gear mass, the rebound rate generally stays the same. Unless I want to go "bonkers" in the mountains. Then the rebound damping goes up one click. It goes back to the prior setting for freeways.

Hope that this make sense,

Marshal

We could just say that preload only affects sag. It does not change the way the spring reacts after being compressed and released - as in hitting a bump.

Sag is a subjective figure, some bikes like more or less, some riders like more or less so there is no one number that fits all bikes and riders but sag is objectively changed by weight. Adding a passenger increases sag. It's simple - the spring is compressed a little more by the extra weight right over the ST's rear wheel. Either the extra sag doesn't bother you, it quite likely doesn't, but it does affect the steering geometry and if you wanted to keep the handling set up you like then you probably would add a little preload to keep the sag you originally dialed in. No? Then your sag changes when you add a passenger. Just having a stiffer spring wouldn't change this.

The 900 (?) in/lb rear spring is adequate for light riders that do not carry passengers or much cargo. The relationship of free sag to static sag for rear springs found in any number of suspension uning guides bears this out. The rear spring is inadequate for heavier riders though and anyone that carries a passenger no matter the weight is too heavy.

 

[Marshal_Mercer]

We could just say that preload only affects sag. It does not change the way the spring reacts after being compressed and released - as in hitting a bump.

Sag is a subjective figure, some bikes like more or less, some riders like more or less so there is no one number that fits all bikes and riders but sag is objectively changed by weight. Adding a passenger increases sag. It's simple - the spring is compressed a little more by the extra weight right over the ST's rear wheel. Either the extra sag doesn't bother you, it quite likely doesn't, but it does affect the steering geometry and if you wanted to keep the handling set up you like then you probably would add a little preload to keep the sag you originally dialed in. No? Then your sag changes when you add a passenger. Just having a stiffer spring wouldn't change this.

The 900 (?) in/lb rear spring is adequate for light riders that do not carry passengers or much cargo. The relationship of free sag to static sag for rear springs found in any number of suspension using guides bears this out. The rear spring is inadequate for heavier riders though and anyone that carries a passenger no matter the weight is too heavy.

Right you are, on all counts.

I purchased the spring that I did based my worst-case scenario, then set sag based upon my average use. To change my bike's for-to-aft bias, I use my rear shock's height adjustment feature. I do not change the sag. That way I can maintain the springs' loads as relatively balanced, as they were before adding or reducing mass.

I realize that the stock-bike owner cannot do this, but it can be done, and IMHO should be discussed.

Interesting topic, huh?

Cheers,

Marshal

 

[dduelin]

I purchased the spring that I did based my worst-case scenario, then set sag based upon my average use. To change my bike's for-to-aft bias, I use my rear shock's height adjustment feature. I do not change the sag. That way I can maintain the springs' loads as relatively balanced, as they were before adding or reducing mass.

I realize that the stock-bike owner cannot do this, but it can be done, and IMHO should be discussed.

Interesting topic, huh?

Cheers,

Marshal

Yes, very interesting. It isn't important to the enjoyment of being on two wheels but some technical aspects of machine design and operation hold my interest nearly as much.

I wish I had the ride adjustment feature even though I don't often need to make such a change. I have seen a riding friend make such adjustments quick-quick on his Ohlins spec Ducati while for me it is laborious to slide the fork tubes up in the clamps which can't easily be done on the side of the road.