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If anyone has Z2s and thinks they are a bit rough over small bumps, I have found the solution and it is:
2.5wt damper oil
That is all. I needed to add a couple of tokens of course, but now it's a lively active fork as it should be,
Surely that's just trading compression damping for spring rate? Which means it'll use more travel for a given energy. Which means more energy for the rebound to absorb, so it'll feel more active. Which isn't a bad thing if you're lighter than average, you want the spring and the damper to be a balance, but at the same time you want the damper to be doing work absorbing the energy, otherwise it's a pogo stick.
It's why position sensitive damping is preferable to volume adjusters, it's just more difficult to implement.
FWIW I just smeared some suspension grease on the inside of the seals which made a massive difference as they don't have foam rings (and use cheaper seals). So it might also just be the service that helped!
Surely that’s just trading compression damping for spring rate? Which means it’ll use more travel for a given energy. Which means more energy for the rebound to absorb, so it’ll feel more active.
Yes, but it's over-damped from the factory, IMO. It's not active enough. I was running rebound and compression fully open and it was still over damped for trail riding.
The design of the compression circuit is that turning the knob pushes the shim stack closer to the ports. So when the knob is far away the damping effect is determined by the size of the ports and the viscosity of the oil only. When you hit a bit enough bump it starts to interact with the shim stack. So essentially, low speed compression is determined by the oil, and the knob determines when high speed damping control kicks in and how strong of an effect it is. But in my view the specced 5wt oil still results in too much damping at low speed. I've used lighter oil but then increased the rebount, and I might run a little more on the compression knob depending on the trail. I still get lots of control, but it's much more active and supple.
Interesting, mine seem to have firmed up a but lately, I was about to do a lowers service
what 2.5wt did you use? fox 5wt teflon infused is recomended?
Also are you just undoing the topcap, pulling it out, tipping away the oil and replacing with 2.5
Yes, but it’s over-damped from the factory, IMO.
Be interesting to see the experiences of others, but that might just be your fork. I'm fairly skinny (64kg) and hate a fork that doesn't have decent small bump compliance (I have a habit of swapping to coil springs), and my Z2 has been grand
but at the same time you want the damper to be doing work absorbing the energy, otherwise it’s a pogo stick.
I think too many folks worry that they'll turn their fork into a pogo sticks when in fact they're probably running the fork too hard/slow. I think most folks could afford to run their forks softer/faster and they'd have a better time.
what 2.5wt did you use? fox 5wt teflon infused is recomended?
Not many people make 2.5wt, it was a toss up between a litre of something for £30 or two little bottles of Rockshox oil which I think is for Reverbs? They can be had for a fiver if you shop around.
As for pogo stick - yes, in theory if you don't have enough damping you get a pogo stick, but my view is that there was too much damping and reducing it has put it about right. For me, and my bike at least. It was to the point that when going fast down a slightly rough fire road it felt like a rigid bike, and it was terribly uncomfortable at trail centres. It was good on big technical stuff though. However, that was with rebound fully open. Now I've got lighter oil, I've put the rebound damper about half way, which gives the same rebound so the same sort of control, but the low speed has been improved.
but that might just be your fork
Interesting but I cant' see how. I honed the bushings, I've added foam rings, I've serviced the lower legs, I even experimented with the shim stack but nothing helped. I can't see that there was much else to change, it's not a complex fork.
Also are you just undoing the topcap, pulling it out, tipping away the oil and replacing with 2.5
Yes, although I used a tube and a syringe so I didn't even have to take it off the bike. I measured 157ml back in.
Interesting but I cant’ see how. I honed the bushings, I’ve added foam rings, I’ve serviced the lower legs, I even experimented with the shim stack but nothing helped. I can’t see that there was much else to change, it’s not a complex fork.
Indeed it is not. My experience to get my sorted involved putting it on the bike, setting sag, finding the rebound setting (somewhere in the middle) and forgetting about it. Only thing left with yours sounds like making sure that everything (external and internal) is straight
I've found mine to be very active and had to add some damping with the dial.
I'm running 115psi, one token, 150mm travel and I'm about 95kg.
I did change the air spring though, and cleared out all the excess grease. I think it blocks the holes that allow air into the narrow shaft that bolts onto the lower legs, as that acts as part of the negative spring these days.
Only thing left with yours sounds like making sure that everything (external and internal) is straight
It works really well now so I dunno.
Maybe it's a question of expectations?
I'm also ~95kg and run it with a bit of compression too.
I do prefer my suspension on the firm side though, I like it to be there to maintain control if I smash into something too hard, rather than something that gets in the way the other 99.9% of the time.
I need to strip my bike at some point though as I'm not getting anywhere near full travel (not that I expect to), but I suspect there's probably tokens in there.
Maybe it's preference then as I tend not to smash into things hard, I float over stuff 🙂
Maybe it’s a question of expectations?
My other fork is a Vorsprung coiled Lyrik, so I don't think it's that. Of course the Z2 can't hold a candle to the Lyrik, but it makes a good go of it
Trutune works well on my Yari
What does small bump compliance mean?
Loads of grip?
Less feeling of bumps through the bars?
Moves lots?
It's a pretty subjective term, right?
Overused?
Is it something you even need or want?
I had these forks in my giant trance and the small bump compliance was awful . Doing some reasearch and found that they dont come with foam wiper seals ! Crazy !! I bought and fitted with suspension fork oil and it was night and day difference . Silly cost cuttting
What does small bump compliance mean?
Loads of grip?
Less feeling of bumps through the bars?
Moves lots?
It’s a pretty subjective term, right?
Good questions, but I think it's like that famous quote about pornography - you know it when you see it 😀
But seriously, for me it's literally the fork overcoming its stiction easily on small bumps, pitter-patter kind of stuff. Not any significant or abrupt hit.
Anyway, sounds like OP has used a smart solution to get the result he wanted. Good work.
But seriously, for me it’s literally the fork overcoming its stiction easily on small bumps, pitter-patter kind of stuff. Not any significant or abrupt hit.
That’s all I’ve ever seen it described as - trail chatter/buzz
Yeah, and anyone who's ridden a decent coil fork will have a benchmark on what "good" looks like.
What does small bump compliance mean?
In this case, it means going fast down stony trails was actually quite uncomfortable as the fork wasn't really moving fast enough so it felt rigid. So too much low-speed compression. Low speed in this case meaning from the fork's point of view, i.e how fast the lowers are moving. On small bumps they don't move as fast because the tyre soaks up some of the first impact, I think. I can still feel the stones in the trail but it's a lot more comfortable on my hands.
Also with new oil it moves around a lot more which is a matter of preference as I like being able to move my weight around and compress or lift the suspension according to the trail. The fork now broadly matches the rear suspension feel for in this respect. I can imagine that if you were on a hardtail this would be terrible,
By changing the oil you are changing the small bump/low speed damping - you can adjust the knobs to bring rebound and high speed compression back to where it was. Even if I dial in more compression damping with the knob it gets less pogo-ey but small bump comfort is still better.
Maybe it’s preference then as I tend not to smash into things hard, I float over stuff 🙂
I'd like to think I do, but my waistline says otherwise 😂
You sure low speed compression is the culprit and not low speed rebound?
When were they last serviced?
Also got conflicting here amongst the thread, some are pinning "small bump compliance" on sticking, others on damping?
What's your sag+token setup? Sure the faster rebound isn't just getting you off of a wall of spring progression?
Also got conflicting here amongst the thread, some are pinning “small bump compliance” on sticking, others on damping?
Think of the stiction as a constant.
OP's lighter damping is helping his fork overcome it more easily.
When were they last serviced?
These are 6 months old, I did a lower leg service and added foam wipers soon after I got them as it was bad out of the box.
Changing sag or tokens didn't so anything to solve the issue. Adding wipers and honing bushings certainly improved stiction, but still just felt overdamped.
Rebound is similar because whilst I changed the oil I also wound the knob back in.
Also got conflicting here amongst the thread, some are pinning “small bump compliance” on sticking, others on damping?
Both can affect the 'plushness' feeling i.e. small bump compliance, but stiction feels different. It's most noticeable on say stony fire road but when you are on big hits it's not a factor so you are feeling damping. If your stiction is high then it feels dead on rough surfaces so you dial down the compression then when you hit big things you end up blowing through travel.
Rebound is similar because whilst I changed the oil I also wound the knob back in.
Anyone know what sort of Reynolds number these dampers operate at? I hypothesized that they might be operating in the laminar region and the transition to turbulent flow is what makes compression dampers spike and rebound dampers pack down. If that's the case then lowering the viscosity and reducing the orifice to match at one velocity, won't necessarily corelate to others.
Is that a serious question or are you showing off? :). The size of the holes and the speed and pressure of the hits, I wouldn't expect the flow to be laminar, in fact I'm sure you'd want it to be turbulent to get more damping effect. Perhaps the low/high speed transition depends on this, although you'd arrive at the correct port size/shim stiffness by trial and error I expect.
It's not a precision system, all I know is that it feels better to me, it cost a tenner and 10 mins.
Perhaps the low/high speed transition depends on this, although you’d arrive at the correct port size/shim stiffness by trial and error I expect.
am I right I. Thinking that there isn’t a mathematical formula for calculating what these things should be?
An interesting thread
Am I correct in thinking that all the above applies to Fox Rythm?
Interestingly I really recognise the effect the OP describes. Uncomfortable on a bumpy fire road. I’ll have to investigate. I had been wondering if it was the 35mm handle bar
I dunno if it applies to the Fox equivalent. I'd assumed that they had a more sophisticated damper. I don't know if it's as easy to replace the oil on a Fox but it shouldn't be hard. Worth a try IMO.
Hmm
A bit of googling suggests that it’s not the damper that’s the same
My question are a prod towards critical thinking, that's my goal.
The push towards critical thinking is due to -
1. I do think small bump compliance as a concept is subjective
2. I do think when people are make small bump compliance a priority, what ever it is in their minds, theyre probably ignoring the compromises theyre making elsewhere
3. even with really good suspension you still feel bumps, to not ever feel bumps should never be a goal
4. it is probably something other than the suspension making your arms tired and it doesn't necessarily have to be the bike
^Should be pretty straight forward to "ball park" the Reynolds number for the flow, you know the oil volume displaced from rebound shaft Cross section x displacement at a given velocity, I've seen velocities banded about by tuners in forums of up to 8m/s in extreme cases, so you'd be safe playing around with numbers between 1m/s and 6m/s as a thought experiment.
Aftermarket seals 🦭 are one answer.
Now, what was the question…?
mine are great, not quite in coil Helm territory but pretty good, after replacing the seals and adding foam wipers.
78kg and they are at 120mm on a steel hardtail.
I will get the aftermarket seals at some point.
I do think when people are make small bump compliance a priority, what ever it is in their minds, theyre probably ignoring the compromises theyre making elsewhere
I love a bit of critical thinking.
It's not like I'm prioritising small bump performance and making compromises elsewhere. Why would you think I'd be unaware of that? I just want to tune my fork until I like the way it rides, and that's what I've done. Sure it might be a compromise on big bike park jumps, but I don't do those. And if I decide to, I can simply change the oil back. I don't see a compromise.
3. even with really good suspension you still feel bumps, to not ever feel bumps should never be a goal
4. it is probably something other than the suspension making your arms tired and it doesn’t necessarily have to be the bike
I didn't say my arms were tired, I said my hands were uncomfortable. These are the same trails I've ridden for decades, on all sorts of different bikes. I'm also an obsessive bike fettler, as you can see from my other threads on this subject, I've tried many things and this change, in my view, makes the biggest move towards what I want the fork to be. I posted it because others may appreciate the tip.
I thought that changing damper oil was an acceptable tuning option for suspension, you seem to be against the idea for some reason 🙂 I do accept that generally you want to keep your gear the way that the manufacturer intended, but this is a budget fork and compromises were made; plus damping setup is a personal thing anyway. It's quite possible that they put 5wt in it because they already have however many thousand litres of it arriving at the factory and it cost too much to order in 2.5wt which is much less common - I don't know. Or they are expecting the forks to be flying high into the air at bike parks.
78kg and they are at 120mm on a steel hardtail.
Yeah I am not sure I would make this change on a hardtail. Mine are on a FS with 160mm rear.
The Fox 34 Rhythm and Z2 share the same air spring, but the Z2 has cheaper steel bushings, no foam rings, cheaper seals, and an open motion control style damper where the oil pours in the top cap.
It's quite possible that the different Z2's don't feel the same, through manufacturing differences, or tuning for OEMs. They do appear on lots of SUV ebike type things designed for touring, maybe they are OEM version tuned for that??
and an open motion control style damper where the oil pours in the top cap.
More like a Novyparts Splug than the plastic MoCo horror.
Shame they didn’t go proper Marzocchi with an open bath
Shame they didn’t go proper Marzocchi with an open bath
You mean a full open path lower? Why would you want that?
You mean a full open path lower? Why would you want that?
All the lubrication, maintenance can almost be forgotten about (if in both legs), seal failures can be spectacular. Basically I’m harking back to a Z1 BAM/Dual
I have some 66SLs on my Patriot (that I'm selling), which are open bath. The small to medium bump sensitivity is good generally because it has separate low and high speed circuits, but the stiction isn't great. On fire roads the fork locks until a slight bump gets it moving again. Not really an issue, but it irritates me a bit. This is because the requirements for damping oil are different to those of lubrication. When I went from Fox green to Fox gold oil (the thick sticky stuff) in my 32s the plushness was another level altogether.