[SylentK]

Actually, I just watched it. You got me curious....

Per Flooks, you want to "just" get the tire off the ground before suspension tops out. This is assuming your spring rate, oil height, oil weight, etc. is all correct. I think I run mine a little bit slower than that.

 

[Slater]

Another thing to consider:

Slowing down your MoCo boxxer to match the rear shock will not feel good, because of the nature of that damper. I suspected it would pack up in the chatter, and it sure did. This is because the stock rebound damper is ported, not a shim stack type. This means the rebound curve is never regressive in high speed, the amount of damping always increases with the increased shaft speed. Because of this, in order to not have to much damping at higher velocities, you need to have it pretty much like a pogo stick at lower speeds, in the parking lot.

Also keep in mind with regards to the Flooks video that he's only talking about low speed rebound, the less important of the two. For high speed you really need to get on the trail!

 

[The Breaker Man]

Another thing to consider:

Slowing down your MoCo boxxer to match the rear shock will not feel good, because of the nature of that damper. I suspected it would pack up in the chatter, and it sure did. This is because the stock rebound damper is ported, not a shim stack type. This means the rebound curve is never regressive in high speed, the amount of damping always increases with the increased shaft speed. Because of this, in order to not have to much damping at higher velocities, you need to have it pretty much like a pogo stick at lower speeds, in the parking lot.

Also keep in mind with regards to the Flooks video that he's only talking about low speed rebound, the less important of the two. For high speed you really need to get on the trail!

But the real question is: can you make a MoCo Boxxer pack up as bad as your old Dorado??

 

[Slater]

Absolutely nothing can pack up worse than that 8lb hunk of crap!

 

[MarkDH]

Another thing to consider:

Slowing down your MoCo boxxer to match the rear shock will not feel good, because of the nature of that damper. I suspected it would pack up in the chatter, and it sure did. This is because the stock rebound damper is ported, not a shim stack type. This means the rebound curve is never regressive in high speed, the amount of damping always increases with the increased shaft speed. Because of this, in order to not have to much damping at higher velocities, you need to have it pretty much like a pogo stick at lower speeds, in the parking lot.

Also keep in mind with regards to the Flooks video that he's only talking about low speed rebound, the less important of the two. For high speed you really need to get on the trail!

That's some good knowledge right there, I hadn't even considered that they are different damper circuits (assuming Vivid is shimmed rebound?). I think I may still slow down the front end slightly though as I get a bit of a 'springy' almost undamped feel when I use a root as a small kicker or something. Just tame it down ever so slightly, I think I have it a little too quick.

Also thinking about the Vivid, it appears to me to be essentialy position sensitive rebound adjustment, like high speed when returning from deep in the travel and slower speed when returning from just a little bit into the travel? Would an 'ideal' set-up have a completely linear rebound speed throughout the entire stroke, achieved by more a more heavily damped high speed and a lighter damped low speed rebound?

 

[Viv92]

Would an 'ideal' set-up have a completely linear rebound speed throughout the entire stroke, achieved by more a more heavily damped high speed and a lighter damped low speed rebound?

Other way round... more LSR less HSR. Read Sockets post again. Too much HSR and it will pack up over repeated hits.

 

[bsphere]

Also thinking about the Vivid, it appears to me to be essentialy position sensitive rebound adjustment, like high speed when returning from deep in the travel and slower speed when returning from just a little bit into the travel? Would an 'ideal' set-up have a completely linear rebound speed throughout the entire stroke, achieved by more a more heavily damped high speed and a lighter damped low speed rebound?

The Elka Stage5 rebound is speed sensitive, resulting in a more predictable ride than position sensitive rebound (according to Elka).

 

[MarkDH]

Other way round... more LSR less HSR. Read Sockets post again. Too much HSR and it will pack up over repeated hits.

Viv, that's not quite what I meant. I don't mean slow HSR overall, relative to other set-ups. What I mean is higher amounts of damping force within the HSR 'region' when spring force is strongest, then when it gets into the LSR region where the spring force drops off, have relatively lower amounts of damping to compensate and (I think) maintain a constant rebound rate. Im just wondering if a rebound rate as close to linear as possible throughout the complete stroke is something that should be aimed for, or if the rate should vary depending on position?

 

[Slater]

Yes the Vivid has a shimmed rebound stack.

As stated previously, with rebound position and velocity have a relatively high correlation. With compression there is no correlation between the two, because the shaft speed is completely dependent on external forces (the trail). For rebound it is dependent on Spring force trying to extend the damper. At 15mm of shock stroke, there is simply not enough spring force stored to extend the shock at high velocity. However at full bottom out, there is a massive amount of force stored in the spring, so you can easily attain high shaft speeds, and always will when returning from bottom out.

A "linear" feeling rebound is not technically the ideal, but it may be what you prefer. For maximum traction and tracking your ratio of spring force to damping should increase throughout travel, but at a non-constant rate. Meaning that as your spring force is increasing, your damping is as well, but not as quickly.

 

[djjohnr]

For rebound it is dependent on Spring force trying to extend the damper. At 15mm of shock stroke, there is simply not enough spring force stored to extend the shock at high velocity.

There is a good amount of discussion about this farther back in the thread, previously rebound being mainly a factor of spring rate had been my assumption as well.

x'' = − k⁄m x
where x = position, x'' = acceleration, m = mass, and k = spring stiffness.
http://www.myphysicslab.com/spring1.html

This shows the relationship between spring position and acceleration.

My take on it -

Mass is the mass that the spring is pushing against, and it has an equal say in acceleration compared to spring rate. If there is nothing but air under your back tire mass is simply your swingarm/wheel etc. However if it's encountering resistance from the ground that acceleration force needs to be taken into account.

If you play with the spring calculator on there it becomes apparent that depending on where you place the knee you could get HSR rates fairly shallow in the travel.

 

[MarkDH]

Yes the Vivid has a shimmed rebound stack.
For maximum traction and tracking your ratio of spring force to damping should increase throughout travel, but at a non-constant rate. Meaning that as your spring force is increasing, your damping is as well, but not as quickly.

Took me a minute to get my head round that, but I think I know what you mean. So if the damping force and spring force both decrease throughout the rebound stroke, but not at directly comparable rate (damping force decrease not as great), then overall the shaft velocity will decrease towards the end of the rebound stroke, yes? This leads me on to another question, which is this slow recommendation from PUSH and apparently WC pro's, does this refer to slowing down the LSR, HSR or both? From what I've read so far, I would plan to set my HSR so that I don't get any bucking, then slow down my LSR more than I normally would for the benefits of increased traction and chassis stability that people have noted. Am I along the right lines here?

Apologies for the 'rebound for dummies' questions, but before my Vivid I just had an RC with a blue and a red dial, easy.

 

[Slater]

Yes if you place the knee at a very low velocity you could get a HSR event sooner, as you are just redefining what a HSR event is, and controlling the LSR for a shorter period of time.

Of course if you consider unsprung mass the results change slightly, but the underlying principles still hold fairly well. It is of course completely dependent on the amount of mass, you are correct.

Mark: exactly. It should start rebounding relatively fast, but slow so that there is no oscillation at the end of the stroke. The damper will actually go from LSR for a split second, to HSR, and back to LSR when returning from a big hit or deep in travel. This is of course somewhat of a simplification and generalization, but for understanding the principles, it should suffice.

 

[MarkDH]

Thanks a lot for the help Slater, I will have to set aside a day for getting my settings, eh, set now. Knowledge is power as they say.