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As I understand the TruTune, what it's doing (at least in part) is reducing what I think is called adiabatic compression. Based solely on some googling, if you compress the air spring really fast, the heat doesn't have time to transfer and the spring ramps up. Alternatively, if you compress is more slowly, it's more linear. I think air springs are referred to as speed-sensitive for this reason. TruTune supposedly reduces adiabatic damping, so theoretically it has more support when compressed slowly but less when compressed very rapidly t, so it doesn't spike at high shaft speeds and you can use more travel.
Hopefully someone who actually knows what they're talking about will come along and clean that up a little.
Noken way simpler. Just a little more positive spring volume. What that does is pretty straightforward.
I can't say whether my tire is bouncing off the ground or not, but I can assure you that my ride feels much, much less harsh with the rebound opened up. That's why I run it fairly open, along with 90% of World Cup DH racers.
Sounds like a VERY viable business plan to me if you get enough people on board with the idea 😂
I'm not a suspension pro by any means, but could that be a sign of packing if speeding up the rebound solves the harshness? @The Enginerd
I'm also not sure what very very fast rebound is exactly, but I typically setup my bike to be a click slower than the tire bouncing in the parking lot test, and then adjust on trail if the tire feels skittish on turns. (Basically, trying to run my rebound as fast as possible as long as I feel i have control)
I was also making an estimate based on a statement over the internet- I could be wrong. I've just seen similar things in the past where people keep backing off the damping because the ride is harsh, when ultimately, going the opposite direction solves the problem.
IIRC, truetune stated a recommended service life of 100 hrs at launch. The said that was a conservative estimate and have since abandoned that 100hr service life.
In theory activated carbon inside the truetune will absorb oil, but I believe there is a membrane to limit oil contact in the insert.
Another note about tru tune. I like their short insert better than a regular volume reducer in my 36. It provides about the same ramp up as a single token, but feels like the progression adds up more linearly. I don't like the sudden "wall" of progression from regular tokens, and find the tru tune short insert to be a better feel.
I usually run 0 tokens, maybe add one if i get too fat over the winter rather than upping pressure.
Using data acquisition over the last few years, but be rarely seen anyone with with rebound too fast. We used it on Teamrobot bike in Laguna and I don’t remember it being too fast. (I can check the recordings)
It’s a balance between compression speeds and rebound speed is where the key is, parking lot test doesn’t really mean much in my opinion. If you are hitting chatter at 30mph vs a steep trail with lots of grip, the bike setup will change dramatically.
I know this is veering off topic, but I was more so looking for feedback on my heuristic - is it inherently wrong to try to run rebound as fast as possible given a riders ability to maintain control?
There’s so many variables, so I don’t think there’s a blanket setting to say “run it as fast as can to hold on” but typically like TeamRobot mentioned the ride is much less harsh with the rebound fast. I’m running my zeb all the way open and it’s still not that fast. So far the only forks that have rebound damper in stock form that can go “too fast” is the manitou Dorado and Suntor DH fork.
But the higher spring rate you run and the harder you hit things the faster the rebound will react
"Run rebound as fast as possible given a riders ability to maintain control" is basically my heuristic, too. Until it actually throws me off, it's not too fast. So, for instance, I will slow it down a little if I'm going to be riding exclusively lower speed trails, especially if they're slick. But otherwise, yeah, I think suspension packs up a lot. Yes, it's true that running firmer suspension can help keep you from getting bogged down in the more progressive/higher spring rate zone of your travel (as Enginerd alluded to with his comments on compression damping), but so does running faster rebound. In my opinion, a lot of people are packing up a lot of the time because whenever they've tried faster rebound it "felt weird" in the parking lot or on the first lap.
This is the correct take.
Run it as fast as you can until either it top outs or it responds too fast for you and you lose a bit of control.
Riding a fast track where your getting faster each run on it, you can open rebound a click each time and notice performance will get better and better, provided you have the energy to keep up with it.
Also Robots method of using LSC primarily and then maybe using a tiny bit of HSC is also the best option with his dampers, LSC on a charger damper shifts the entire damping curve, and therefore affects HSC rates, so it's always LSC first, then HSC if you really need it after
My add to the faster rebound bandwagon: if the rear kicks when going off a lip, start by speeding up fork rebound rather than slowing down shock. If it feels balanced off lips after that but too active to hang onto, that's when you'd close both fork and shock rebound 1 click.
So where are folks at with sag on zebs?
Others on here know more, but maybe I can spare you an onslaught of lectures about all the problems with relying on sag as anything other than a starting point. I actually just measured my sag because I was swapping in the current gen air spring for the prior gen. Chasing a less divey midstroke, and counting on a TruTune to address the new spring having more ramp up.
I'm at 18ish%, but I also have burnished bushings, the Diaz lower alignment treatment, and new SKF dual compound seals. Sag can tell just as much or more about friction problems as spring rate.
I think the best use of sag is what I did: use it to compare spring rates between different springs. Otherwise, I generally put more stock in starting with the trailhead app or similar recommended pressure and going from there based on feel, how much travel I'm using, front-rear balance, etc.
It'll take you a minute to find and digest, but there are some great threads on this site and other places that have really helped me.
Appreciate it but I’m well aware of not relying too much on sag. Mainly just curious where folks have ended up.
Depending on the trail I’d be 20-25% in the parking lot, static. 180mm of travel. This will translate to 22-27 maybe 28% dynamic while riding
So here comes what will probably be a thoroughly confusing and contradictory reply - yes, your rebound can definitely be too fast and some rebound control is very important. However when I set up a bike it might feel quite fast and hit some high numbers in data too.
"packing" or the perception of packing can be several things-
spring rate too low - rides low and there isn't enough spring force to return to a reasonable ride height
too little compression damping - wheel compresses too far which either dives or overshoots the bump, then has to travel farther than it should to get back to sag.
too much low sped rebound - "ratchets" the bike in to its travel, even on smooth ground or smaller bumps, also quite pronounced on rear suspension with high anti rise that also compresses the shock.
too much high speed rebound - shock hangs up when trying to return from the end of the travel.
If the rebound is too fast it can do a few things - the bike will return too fast and overshoot sag which feels unstable, particularly low speed situations. Or it can return so fast it bounces off the ground, reducing grip.
Rebound only needs to be fast enough to get back to sag in the shortest possible time - any faster than that doesn't achieve anything, and is mostly dictated by your spring rate so continually winding the adjuster out might not be increasing the speed since the spring can only extend the mass of the wheel or the rider at a certain rate, even with no damping at all.
Thinking the wheel needs to return as fast as possible only works when looking at a single bump or impact- an underdamped bike will continue to bounce up and down which means it might not be in the best place for the next bump - its doesn't "know" when to stop, so your damping is the only thing that can respond in a way thats proportional to the impact.
personally I like relatively light low speed damping (comp and reb) which allows the wheel to flutter over bumps, with enough high speed damping to control big bumps. on rebound thats linear to slightly progressive, while compression might be slightly digressive. This usually gives something that "feels" fast, and will hit some high numbers on the data logger but there is still control there and for most people the dials don't need to be wide open either - I feel like whenever someone recommends fast rebound they instantly mean winding out the dial, which often doesn't increase the max speed at all - and if it helps its more like a band aid on some other issue
Same. I haven't actually measured it in a long time, but the last time I did, the TrailHead recommendation was giving me about 18% static sag running Motion Instruments. When I finished tuning with that, I tended to end up with around 27-29% dynamic sag front, 30-32% dynamic rear. For my forks at this point I just start with whatever TrailHead says based on a realistic riding weight (like, actually step on a scale with gear and check), and maybe add like 1-2 psi. Rebound I usually run about 3 clicks faster than TrailHead says.
I'd actually totally agree with all of this. In guess my advice should have been caveat-ed with more info about spring and compression damping setups.
I disagree personally with low LSC, or at least that isn't possible with the forks I use, in my opinion there is a minimum amount of LSC required for stability, then final tweaking with HSC and or tokens.
Rebound only needs to be fast enough to get back to sag in the shortest possible time
This is 100% true and how i always try setup my suspension.
Yeah I also agree on the LSC thing - I realise I over-generalised the comment about "ideal" tunes, and there does need to be sufficient control of pitching/stability from the low speed compression damping. I personally hate the feeling of an unsettled bike too
It's something I was giving a lot of thought to over the weekend at the Crankworx DH - there is a large overlap between the fastest "low speed" scenario and the slowest "high speed" (ie bumps) impacts but what I think happens with some digressive dampers is the "low speed" section of the curve is very steep but blows open too early which makes it very harsh on the small bumps (high frequency chatter is usually too short for the damper to accelerate very far) but also feeling like it lacks support. I see a lot of shocks with what I would call an extremely soft tune but riders complain thats its too hard on bumps
Oh yeah I keep using quote marks because the speeds which a typical low speed event happens at, the speed the damper moves at and the speed the adjusters work at can all be very different, which is fun!
The Noken was the inspiration for my latest project. The Suppos-air-tory™️
https://www.instagram.com/p/DG5dHgsP1YZ/?igsh=MW9kZmk3YjNlM2cybw==
Thanks for the comments. "Rebound only needs to be fast enough to get back to sag in the shortest possible time" is definitely something I'll add to my mental model when setting up the bikes.
Do you have any thoughts about how air spring progression plays into this discussion?
I know for my self, I have a zeb at 180 with a lift damper ridden with and w/o a noken. With LSC fully open, and air pressure near the recommendations from rockshox and mrp, I'm only getting ~155mm of travel. The fork rides incredible, and feels balanced on a 170r/180f bike, but some of the other stuff I'm reading suggests I should be trying the older zeb air spring (more linear). Appreciate any thoughts on trying to get closer to full travel or just enjoying the bike, thanks.
The previous Zeb air spring would be one step forward (more usable travel) and three backward (worse quality of travel. Hollow mid stroke and harsh initial travel)
This is super cool! How does it work in the field?
***checks calendar, it's not April 1st***
I'd buy it on name alone.
The ghetto proof of concept worked quite well. Hoping to get out this week after work for a more expansive test.
On the ghetto setup I ran the same pressure in the main (low pressure) chamber as I was running previously. Definitely softer off the top and still plenty of support through the mid stroke.
My first thought is that's a little over 85% of your travel. I tend to look for 90% or a bit more on the gnarliest stuff I'll hit on the bike, with the 5-10% in reserve for when I f' up. But if I was running LSC wide open and the fiork didn't feel overly active and unstable, then I'd be working on the assumption something is off.
- Did you put a more than the recommended bath oil in there because, you know, more is always better?
- If your seals are old or you haven't sprung for some SKF seals, I'd pop everything out, check alignment. If it's sticky, you could find a friend with a burnishing tool (opinions differ; definitely don't overdo it) or send off to Diaz. Put some dual compound seals in there. Unless you're a 20-something park rat or live in England, they'll last you a couple of years.
- Stick the stock damper back in there (ughh, I know) and see if you're getting 90%+ with the same spring pressure. If so, could swap to the next lower compression tune on the Lift.
- Stick a TruTune in there. I think it might open up travel more than the Noken. This is the easiest, spend $125ish and see if does what you want option.
For context, I've got a Lift in a Zeb at 170mm with a TruTune. 210 lbs running a blue tune. Hazzard with a f/f tune on the back. The biggest weakness of the Lift is the lack of a good solution for the rear. Adding a bunch of compression damping to the front while still being spring forward on the rear can be weird. A similar tune on the shock will really make the fork sing.
Good luck and hope this helps.
I would second this - even when it came out that generation of air spring was clearly a backwards step or 2. The current air spring is pretty good.
If you're not getting all the travel - a) its not a target, so as long as you get more than about 80% of the travel and it feels fantastic everywhere then thats fine IMO
b) Bushing friction plays a big part - the clearances are quite small and the Zeb has very long bushings so any extra friction from old oil (or lack of, ie sitting at the bottom instead of on the stanchion) can cause them to bind as they get near the end of the stroke. Thats not ideal so worth adressing if thats the case
I would often only use 80% of the travel nearly every ride, but things like jump tracks would slam the o-ring all the way to the bottom on take offs
Post a reply to: Attn Fellow Suspension Nerds - 180mm Zeb won't get full travel?