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I've got a (I believe to be) kinematics related question, specifically with regard to anti-rise and tuning for different steepness tracks. I recently bought a SC Vala, which switches to 4bar from VPP, and compared to the other SC bikes, one of the traits that stands out is that the AR stays consistently lower (~70% iirc) as opposed to dropping from high to low depending on travel (~100->60 on a Nomad iirc). I'm using the same suspension on all 3 of my bikes, and set up on my home trails they all feel pretty similar most of the time. But on the Vala, when I am riding the brakes on steep chunky trails, or doing a step down into brake bumps (braking after landing to make a corner after), I notice it feels like it see-saws a little bit. Is there a single compression setting I can change before I ride these trails? It feels really good aside from that, and it's not bad in those situations, just not ideal. I'm thinking that I'd want to add HSC to the fork to fight the extension of the rear.
With they way you describe it it might be more an unbalanced front/rear rebound damping and either your rear rebound is too fast or your fork is a bit slow.
There’s not really a single setting, the other issue of that you can change the feel of the bike in every other area of the trail. I would slow down the shock rebound, stiffen the fork HSC and speed up the fork HSR.
High AR and low AR have different feels and it might just be something you need to get used to and how to use it. I’m in the opposite postion where my DH bike has low AR and ebike is high AR. So I get such a stiff feel from shock when braking.
I would add more low speed damping to the rear - rebound will slow that extension, but you might find adding compression damping helps too. Bracket both of those individually and see what helps.Increasing the fork damping won't prevent the rear from trying to extend
Ok, makes sense what both of you are saying. One follow-up: I assume by what you're saying that speeding up fork rebound will not really help? I ask this because I've learned in setting up suspension on my bikes that if, say, the rear feels like it's kicking on lips that speeding up the fork rebound is usually the better solution. I try to err on running rebound faster rather than slower, but OTOH it would make sense that if I know I like rebound 3 clicks faster than the RS shocks on a VPP, maybe I only need to go 2 faster on a lower AR 4-bar.
I don't have a ton to add here to the suggestions you already got. One thing I would say, is that I have found pretty big variance from one grip x2 fork damper to another with regards to rebound settings. Also, I find that I cannot run rebound quite as open as santacruz suggests on the vala/bullit setup pages. In contrast, I run the float x rear shock rebound faster then what they suggest. Compression settings I run largely what they are suggesting more or less.
My guess is that your fork rebound is quite a bit more open then your rear shock. Have you checked the volume reducers in the fork? IIRC santacruz was shipping the vala with 3 tokens in it, which can make the deep stroke rebound feel a bit frantic.
I took the Fox stuff off and am running a Zeb and Vivid air, which I am also running on my other SC bikes.
In that case, I'd check the tune on the rear shock. Within my group of folks with both vala's and bullit's, there have been a few attempts at fitting aftermarket shocks with off the shelf medium tunes. Those efforts were not successful and only when the tunes were changed to the santacruz specified float x2 and dhx2 tunes, were those aftermarket shocks an improvement.
Obviously, the vivid is going to be a different animal, but I only mention that santacruz did a pretty decent job with their oem specified tunes, and that aftermarket off the shelf tunes may not be suited perfectly.
RS does a C37/R25 tune for the SC VPP bikes where you can buy retail bike-specific tuned shocks. I've got that C37 tune in my Nomad 6 and Heckler SL. My Vala's shock is C34/R25, and am running a little bit more compression damping than I do on the other bikes to compensate. I bumped up from the stock 1 volume band to 2 just like on the other bikes have.
One thing to keep in mind is that, because both rebound and compression damping exert a force proportional to the shaft speed of the shock/fork, all changing these will do is alter the amount of time that it takes for the fork to dive and/or the shock to extend under breaking. During sustained braking, all you can do to prevent the fork from compressing more is add volume spacers and the only thing that can prevent the shock from extending is anti-rise.
Honestly the key thing is that there is never one "right" answer every time - it's always best to note your settings and bracket through different changes yourself. What worked on one bike might not work on another. You can work out what might probably be the best thing to change but I would still try both more and less of that adjustment, and be prepared to move on to the next change if it doesn't help. Start with spring rate, then move on to compression an rebound.
Generally, any kind of instability/pitching needs more damping to reduce that feeling but it could be due to the spring as well
As a rough guide, you can think of the spring changing how quickly (in time) the bike returns to sag/steady state, and damping changes the number of times it bounces before reaching that point. So a soft spring with lots of damping will only bounce once but take a long time to get back to sag, whereas a stiff spring with no damping could take less time to reach steady state but will bounce more times before it gets there. The best setting is somewhere between that
Got it, that makes a lot of sense now (more damping to reduce oscillation). If the rear end is extending too rapidly for my preference, then (barring being able to change the kinematic) I need more rebound damping. Then maybe I'll try a click more fork HSC to similarly slow down oscillations up front. I feel like spring rates are pretty dialed in (bike feels pretty balanced in other situations). The sensation isn't too pronounced, but I can think of a couple spots on local trails that I can use to use to test changes on - like a small step down into brake bumps right before a shallow catch berm.
How does overall progression affect rebound speed? assuming that you make zero adjustments to a shock, will a more progressive setup have slower rebound speed deep in the travel, and faster rebound speed at the top of the stroke? Or, does overall progression not really affect rebound speed one way or another? Is it super complicated because it depends how position vs speed sensitive the damping is in a given shock?
I closed the shock rebound 1 click and it felt better on a quick power hour after work - more stable in braking situations. Thanks guys, good learning experience.
That’s a good question about rebound and leverage rate: From Google search;
Yes, the leverage rate of a suspension system can influence the rebound speed. A high leverage ratio will generally result in a faster rebound, while a lower ratio will result in a slower rebound. The leverage ratio determines how much force the suspension system transmits to the shock, affecting how quickly the shock moves.
With a higher leverage ratio, the shock experiences a larger force for a given wheel movement, leading to a quicker extension (faster rebound).
There currently aren't really rear shocks with position sensitive damping in the world of bikes, so shaft speed is the only factor in damping force shock tune aside. There are a couple of things to look at to get a feel for rebound speed. One is the wheel force plot. That factors in spring force which is important because higher spring force deeper in travel promotes a faster rebound speed. The other thing, obviously, is leverage ratio. Leverage ratio is important alongside the wheel force plot because of how it impacts damping force as you feel it would be felt at the wheel, but it's a little more than just 1:1. The damping force at the wheel is inversely proportional to the leverage ratio squared. So while the shock might be pushing for faster rebound deeper in travel at a lower leverage ratio, the damping is able to do more to slow rebound than at top of travel. To me, the big takeaway from this is that if you compare a setup that gets a certain wheel force plot by using volume spacers or progressive springs and then compare it to a setup that gets the same wheel force plot but by adding progression with a linkage, you get a more consistent rebound speed across full travel with the linkage version.
Very interesting, thank you!
Sag doesn't always equate to supple/not supple and harsh can come from blowing through travel too quickly with too low of a spring rate, wrong tune for terrain and riding style, both, neither, etc and so forth just as much as harsh can be from running a 600 pound spring and being too light to get that sucker to compress.
Adding to this and tying back into damping force as you feel it at the wheel being inversely proportional to leverage ratio squared, if you are riding too deep in travel it’s easy to find yourself in a spot where you get spikes in damping force more often.
Thanks for all the discussion on this. I tried a few things since last posting.
I didn’t have a heavier EXT spring but I tried opening the rebound most of the way, completely opening HSC, and almost closing LSC. It seemed better. Poppier, less “wrong” but still harsher than I’d like. Previously it just felt bad in so many ways it was hard to describe, but now it felt better all around. More predictable. In my mind, closing LSC and opening rebound would get me higher in the travel. So maybe a stiffer spring is the way to go…
Then I put on a DHX2 with a 325 spring (300 on the ext). It immediately felt better. Travel felt deeper, less harsh, way poppier, more supple. Pushing on the suspension in my garage, the EXT felt like it hit a wall at 20 ish percent travel. The Fox felt more linear and smoother all the way through.
I’m going to try a sprindex on the fox. I’d sell the ext in a heartbeat if the fox is just that much easier to set up. It was tuned for a medium mach 6, so probably the right ball park for me.
Maybe I don’t like the over damped feeling (?) of the ext. still not dialed though.
It takes time to get things set up, be aware the sprindex will add some progression to the end of the stroke,
Of course. With the dhx2 it seems possible, with the EXT I couldn’t see light at the end of the tunnel. Thanks for the note about the sprindex.
Question about air shocks on highly progressive suspension systems - in my mind i can see no issues with large volume air shocks on progressive systems, it just seems like you would be gaining more sensitivity for similar bottom out resistance, or same sensitivity for greater bottom out resistance; Is there a percentage point say 30% 35% or 40% progression where you believe an air spring is no longer a viable option? or is the progression of the air spring negligible and over hyped and simple fear mongering by “big coil”.
Yup very much can be an issue, depending on the exact shock and also stroke length. Large volume shocks like the X2 are OK up to about 35% but something like a Megneg doesn't work very well when you go much past 30%. The smaller neg chamber RS shocks work OK though. This is especially noticeable on short travel <55mm stroke bikes, since the larger negative volume gives a vague feeling around sag so they will tend to sit very low in the travel.
So its not a simple answer but it is a factor in anything over 25-30% progression
I'm running a Vivid with 2 bands & HBO still maxed out on my Heckler SL using a Cascade link, which puts it at ~35% apparently. It's great, no desire to take band(s) out after putting the link on. I love never having hard bottom outs.
Large volume air shocks like the X2 and Vivid arguably work better on higher progression layouts, as they lack mid-stroke support compared to coil shocks and have minimal ramp at the end of travel. See Sram's graph for reference:
Thank you for this!
Thoughts on chainring size and suspension performance?
What percentage change does going from a 32t to a 34 or 36t make to anti squat and does that make a noticeable difference in downhill suspension feel? I’ve heard it’s not much of a difference but have never seen numbers put to it.
There is no general answer, it depends on bike to bike. But as far as pedal feedback, the decrease in kickback angle is proportional to the percentage change in chainring size, so 32/34-s of the pedal kickback when you go to a 34T from a 32T and 32/36s going from 32T to 36T (and 34/36s in the third case obvs).
Pedal kickback is a factor of how much chainstay length increases and thus how much the chainring has to turn to compensate for that.
The rear cog you are in will make a much bigger difference than the front chainring. I always try and descend in the smallest rear cog.
Try the difference between biggest and smallest to see if you can feel the difference
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