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Fox Grip 2

Katz

Monkey
Jun 8, 2012
371
788
Arizona
I was only trying to point out where some of the confusion seems to come from, but it sounds like I confuzed it moar..
It's all good. These posts will be useful for some other confused individuals at some point... hopefully, haha.
 

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,987
1,352
SWE
without enough preload on the high-speed shim stack, the shims start deflecting prematurely and some of damper fluid ends up totally bypassing the low-speed orifice
That's been my understanding as well, that some preload is necessary.
My experience is that preload is not always necessary. Preload will for sure increase the range of the low speed compression but my somehow limited understanding is that lack of low speed damping can be misunderstood as lack of high speed damping at the early shaft speeds opening the shimstack from the piston. As @Steve M explained in one of his newsletter, some piston have such large ports that just lifting the shimstack a tiny bit will create a huge flow area, or a least too big to create any damping.
Maybe he can explain it better than I do or tell me what I didn't understand ;)

I have been playing with the ABS damper of my Manitou fork. It came with preload on the shimstack. Now, without preload, the fork is more responsive, like if it reacts faster to bumps. The downside was that it made the shortcomings of the air spring more obvious: I run relatively low pressure and a small positive chamber which gives not much midstroke support. I will go with higher pressure and less token next.
I have the same experience with a DHX RC4, I had first a rather weak stack with plenty of preload and went for almost no preload and a much stiffer stack which gave me a much more responsive rear end.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
1. Damping is damping
There's a few people missing this simple fact.
Whether oil is flowing through a static orifice (i.e. port), a dynamically variable orifice (i.e. shim stack and/or coil spring preloaded shim/s), whether the primary flow path is the LS port or HS port/s, none of these definitions mean anything when it comes to actually riding. LS/HS are merely names given to adjusters which control arbitrary parts of a curve, often with huge overlap. What does matter is the resultant curve, and depending on the damper geometry, a myriad of different setups can give a similar shaped curve.

Unless you're comparing different valving preferences on a geometrically identical damper, you're only serving to confuse. Nothing much in the world of passive oil dampers (at least for MTB purposes) has changed in the last few years: so for those chasing/claiming some "magical new way" of setting up a conventional damper that's made improvements in leaps and bounds, well... either you're delusional, or your setup sucked before.

2. Travel matters
In my experience, there's a lot of people on mtbr (and increasingly, here) riding bikes with incredibly small amounts of travel and getting overly pedantic about suspension setup. While there's no reason to not optimise every amount of travel / every type of bike, if you're on a 130mm travel bike then you've created a pre-handicapped scenario where you need to run a higher spring rate (directly in proportion to the travel reduction) to not bottom out. If you increase the spring rate in proportion, your suspension performance (traction, bump absorption) will suck compared to a 170mm+ travel bike. If you don't increase the spring rate in exact proportion, you now have to compensate for the undersprung setup with damping, and your fantastic unicorn setup is actually just a terrible web of compensation inapplicable to anyone else.

The same tuning concepts should apply regardless of travel, however in reality, larger travel magnitudes (170-203mm+) favour bump absorption and traction - leaving chassis stability (particularly pitching) as a key problem that needs to be managed. Smaller travel magnitudes (<160mm) inherently have far less problems with stability, and far more problems with bump absorption and traction. These are competing (and often opposing) factors - which means the compromise you've made for your bike may be the complete opposite of what is appropriate for someone else's.

Here's what I propose:
If you're going to discuss suspension tuning and suggest great new ideas, start by detailing the front and rear travel on the bike you're riding, and some details of the terrain and riding you're tuning for. Body weight and F/R spring rates, along with an average rear LR would be good additions. Then detail the problem you had, and what you believe fixed it. That way people can decide if there's any crossover or relevance to their own application.
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,454
10,089
AK
I don't find those mutually exclusive, a good example was a Fox Performance FIT fork from something like 2013, 100mm XC fork. Used it for a season or at least a partial season. Because it had no low-speed stability, I had to run a crazy spring rate in that thing, which made it suck at absorbing bumps too, it could have just been a massively over-stacked main piston, but even at the 100mm level, I was faced with crazy pitching and no stability, or having to jack the spring rate way up to provide that stability, which was ultimately the better solution, despite the poor bump performance. It was a shitty situation though.

I do see that this can get magnified with bigger-travel bikes, but I don't see it as the last word either. The damping still matters significantly on both. I recently had a 34 that I was trying to overcompensate for a crazy over-damped high speed circuit, it was stable enough, but I was having to run crazy low pressure to try and get it "soft enough". It simply had to be revalved. I have a virtually identical 32 (not the same one above, a 2018) that runs better, more controlled, etc. Again, these damping problems aren't exclusive to 170mm+ bikes.
 
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Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
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I didn't say they were mutually exclusive, and certainly didn't say the same issues can't apply to both travel brackets. However if you're experiencing significant issues "from the other bracket", then chances are you have a significant setup error - for example, what's "a crazy spring rate"? When you only have 100mm of travel, the correct spring rate is going to be very high compared to even a 150mm travel fork (like I said, the spring rate increase needs to be directly proportional to travel decrease to avoid bottoming out) - so in these cases there's a high chance that what you think is firm is still undersprung. The mention of "crazy pitching and no stability" with just 100mm of travel reinforces this.

It doesn't help that often shorter travel = inferior dampers (the examples you gave fit this category unfortunately), but in a scenario where you're considering the same damper in correctly sprung suspension with lower travel, what I say does indeed apply.

Anyway, if everyone fills in travel and problem details like you just did, the applications which solutions might be relevant for become clearer.
 

Jm_

sled dog's bollocks
Jan 14, 2002
19,454
10,089
AK
I didn't say they were mutually exclusive, and certainly didn't say the same issues can't apply to both travel brackets. However if you're experiencing significant issues "from the other bracket", then chances are you have a significant setup error - for example, what's "a crazy spring rate"? When you only have 100mm of travel, the correct spring rate is going to be very high compared to even a 150mm travel fork (like I said, the spring rate increase needs to be directly proportional to travel decrease to avoid bottoming out) - so in these cases there's a high chance that what you think is firm is still undersprung. The mention of "crazy pitching and no stability" with just 100mm of travel reinforces this.

It doesn't help that often shorter travel = inferior dampers (the examples you gave fit this category unfortunately), but in a scenario where you're considering the same damper in correctly sprung suspension with lower travel, what I say does indeed apply.

Anyway, if everyone fills in travel and problem details like you just did, the applications which solutions might be relevant for become clearer.
Pressure well above recommended and barely any sag (if any, maybe 10mm?). Some of those older fox forks blew through travel like Rob Ford on a cocaine binge.
 

Katz

Monkey
Jun 8, 2012
371
788
Arizona
Anyway, if everyone fills in travel and problem details like you just did, the applications which solutions might be relevant for become clearer.
I'm going to add this as a data point. I'll outline everything that I think is relevant to the overall balance of a rider/bike assembly but since this thread is about Grip2, I'll focus on changes I've made to the fork.

Bike:
  • Nomad V3, size L. The catalog specs show 438mm reach/609mm stack and 433mm CS.
  • 780mm 15-mm rise handlebar, 50mm/0 rise stem with a 5mm spacer underneath
  • Everyday tire combo: E13 TRSr classic (rounder profile and longer lasting than the new one) @ 23 psi up front and CST Rock hawk EPS (88% as good as Aggressor, which makes it 12% unrideabru, but I get longer life at 50% price) @ 26 psi rear, Cushcores both ends, 27mm inner width rims. IOW, quite a bit of front bias in terms of friction coefficient & mechanical grip to mitigate understeer on loose surface
  • 32.3 lbs ready-to-ride

Suspension:

  • NA1 36 set at 175-ish mm travel, roughly 40% more negative chamber volume over stock NA1 using a combination of NA1 air shaft, NA2 top out bumper and negative plate, MRP Fulfill, Grip2 damper cartridge
  • Float X2, no mod. Code C975. 2017 model, rebuilt by Fox in September 2018. They advertise that they upgrade to the latest valving upon rebuilding, but I really have no way of verifying it, Running 175 psi with 3 vol. spacers (max. recommended by Fox). N. V3 has a typical VPP parabolic LR curve, averaging about 2.37 throughout 165mm
The hack behind the bar:
  • 5'10", 32-inch inseam pants, 175-ish lbs naked, flabby but not fat with XL head on semi-broad shoulder (forward weight bias)
  • Not fast but not a total Joey - managed to get within top 5% on a few Strava segments with large pool (1200~2700 specimens) in Sedona and Las Vegas when I didn't take beer breaks (Guinness Nitro FTW). However my jumping skills are at the average dentist level
Primary riding terrain:
  • Loose kitty litter pebbles over packed kitty litter pebbles, with many pointy lava rocks and granite poking out of ground. We don't really have dirt, sucky.

Problems/complaints

  • My left hand suffers from carpal tunnel syndrome, and I severely jacked my right wrist last August. With the air pressure/damper settings favoring stability on high-speed janky sections, the fork was feeling a bit harsh when riding at casual pace (70% of the time) and my hands were going numb every ride
  • Understeer in the latter half (apex to exit) of flat turns. I could get the bike to turn just fine as long as I employed proper techniques, but the front tire always started to wash out before the rear tire, often in very unpredictable manners because of our Loser “dirt” or whatever you want to call the opposite of hero dirt. *this wasn't really a complaint as I learned to deal with it, but adjusting compression damping ended up having positive effects
The fork settings as of October 2018 (Grip2 installed, but prior to the latest air spring mod):
  • 76 psi in positive chamber, 85 psi in negative chamber, one blue vol. Spacer cut down to 9mm thickness.
  • HSC 20 out (all way open and then some, I learned later), LSC 12 out, HSR 6out, LSR 13 out
I began keeping track of damper setting after I installed the Grip2 in September 2018. This was the last input on my spreadsheet before modifying the air spring, so this was as good as I thought I could make it, with commonly-accepted "LSC for support, HSC for big hits" mindset. My hands were still getting numb mid-ride, and the front tire washed out easily if I weren't careful.

Not happy with the result, I looked further into improving the fork's sensitivity. I started to look for ways to increase the negative chamber volume on budget (I'm cheap)

The fork settings as of December 13, 2018 (post-spring mod):

  • 76 psi in positive chamber, 85 psi in negative, one Neopos
  • HSC 10 out, LSC 8 out, HSR 7 out, LSR 13 out
The spring mod greatly improved bump sensitivity. It allowed me to run the HSC/LSC settings recommended by Fox without beating up my hands too badly, but I still ended up backing off LSC by additional 2 clicks. There wasn't any perceivable improvement in handling over the previous settings, which really wasn't a part of my objective at that point. So I was satisfied with these settings, even though the bike still understeer'ed, often coming too close to grazing cactii and other pointy desert vegetation towards the exit of turns.

The current fork settings:
  • 81 psi in positive chamber, 85 psi in negative, one Neopos
  • HSC 8 out, LSC 12 out, HSR 7 out, LSR 14 out (all way out) *I mentioned I ride with HSC 7 clicks open, but I misspoke.
I'm guilty of changing too many things at the same time, I had a custom piston from @92SE-R up until this point, but I went back to the stock piston as I was unable to use full travel of the fork. Hence the bump in positive chamber pressure. The piston increases negative chamber volume at the expense of reduced positive chamber volume - works great for shorter forks, but it was a bit much for 170+mm travel and my body weight.

After reading this post by @Udi outlining how he adjusts Fox RC2 damper, I started experimenting by closing HSC all way, doing figure 8, hopping, etc in my backyard. The aforementioned loose pebble soil makes drifting effortless at low speed.

Exhibit 1
IMG_1718.PNG

I noticed the front tire's cornering traction (in the latter half of turns) got proportionally better with more preload on HSC. My WAG is increased HSC slowed down the compression of the fork as I brake/get low into a turn, so that the fork carries the compression/preload deeper into a turn before it starts rebounding (release of weight stored in the spring = extra traction), whereas it sprung back to the sag point by mid-turn previously with less HSC and very little rebound (which I prefer). Or something like that, I don't know :confused::) Whatever the explanation may be, it worked well in my particular case.

Once I got the bike on the trail, I found HSC 5 clicks open was about as much preload my hands could tolerate without getting numb. So I left it there for a couple more rides. No perceived decrease in support, even though I backed off LSC to 12 from 8, and my hands were happy.

All was well until the bike nose-dived enough to make me pucker up when I tried to pop off a small lip at 20+mph. Tried few more times at various locations with the same result. Backing off LSC didn't seem to have much effect. My LSR was already all way open, with HSR 7 out (only 1 click left to full open). After a few more rides, I settled on HSC 8-out as a good compromise of bump sensitivity, cornering traction, and pop. I realize this is largely a rider problem, but for the time being, it's better for the well-being of my aging body to back off 3 clicks while I attempt to improve my skills.

I'll keep adjusting the balance between HSC and LSC to see if I can find better overall balance.. If that fails, I'll consider trying 2W damper oil, since I'm running less HSC than what I actually liked in an effort to make the front end pop better and rebound circuits are at the end of adjustment range.

Summary/My take-away (at this moment - learning never stops):
  • Lots of people overlook compression damping and run too little of it in an effort to make the fork supple, which I now know is a wrong approach. If you have sensitive/injured hands like I do, getting the spring sorted is the first step so it won't interfere with compression damping adjustment. Lots of options available these days (coil, Luftkappe, retrofitting NA2 guts in a NA1 chassis like I did, etc)
  • Forget that "LSC for support, HSC for big hits" non-sense.
  • The primary focus on MTB damper tuning revolves around bump management and stability, but the effects on transient handling characteristics shouldn't be ignored. Except for big berms at bike parks (more or less steady-state turns), the majority of corners you encounter while riding an MTB are short and quick. In my case, increasing HSC had far greater effect than lowering the bar/stem by 5~15mm (which did help a little).
tl:dr
Moar negative chamber volume cures ailments your paws suffer from so you can run moar preload on HSC shimz, which makes you feel like a pro under all kinds of conditions. YMMV.
 
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Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,987
1,352
SWE
@Udi
I would say that the need for preload increases with the size of the HSC area, the bigger the area, the more the need for preload. I have no theory or explanation for that, it just comes from observations/experiments I have made. And Steve mentions it in his video about hsc/lsc! :brows:

Fox with its RC2 and RS with its Charger have rather large high speed flow areas on their pistons compared to some of the upgrade kits I have seen from Novyparts and Fast Suspensions which do not use preload. I use one of the french kits in my fork (150mm) and I am very pleased with it. FWIW.

The experiment I did with the RC4 going in the same direction was filling the 0,2mm of dish with a stack of 0,1mm shims with 13,5mm diameter so that it covers most of the openings. It leaves just a 0,5mm gap for the oil flow as long as the shims don't bend. I quite suspect they do... :D (my next plan is to replace the 2x0,1mm shims with a 0,2mm which should be 4 times stiffer) above that I placed a much stiffer stack and got a bike that was loosing less speed on rough downhill sections and achieved better low speed support despite having very little HSC.
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Congratulations, you successfully missed virtually every point I made. :)
 

Happymtb.fr

Turbo Monkey
Feb 9, 2016
1,987
1,352
SWE
Congratulations, you successfully missed virtually every point I made. :)
Ok, thanks anyway! I don't want to get into more trouble ;)

Just one question: what is the relationship between the support you get at the rear wheel, the LR and the shimstack stiffness? In other words: how much more stiff has the shimstack to be if the LR is boosted from, let's say, 2,5 to 3 in order preserve the same level of support from the hydraulic at the rear wheel?
 

Udi

RM Chief Ornithologist
Mar 14, 2005
4,917
1,211
Just one question: what is the relationship between the support you get at the rear wheel, the LR and the shimstack stiffness? In other words: how much more stiff has the shimstack to be if the LR is boosted from, let's say, 2,5 to 3 in order preserve the same level of support from the hydraulic at the rear wheel?
In order:
  1. A good relationship, loving and supportive
  2. Infinitely more stiff, I recommend zero preload and infinite shims
Sauce: I once watched a Tuesday Tune
 

slyfink

Turbo Monkey
Sep 16, 2008
9,575
5,356
Ottawa, Canada
That thread is pure gold!

Who has got the longest...
























... suspension dyno plot in the southern hemisphere? :D
that thread is a gong show, but (I think) there's some really interesting bits of info in there. at least for me. I have a 2016 Pike with a Luftkappe that needs some service. I'm thinking of sending it to Steve to work his magic. I figured I'd get the re-valving done too (I think that's what he does), but now I wonder, based on what Darren posted in his video, whether it's worth the $. Will I feel a difference?

On the other hand, I've been told that shims wear out over time. So maybe a revalve is necessary anyways?

Though I never felt anything wrong with the fork, I never got full travel from the fork (or even close) after I installed the Luftkappe. But then again, I didn't really have any complaints about my Monarch, but my world was rocked with I had him do the Tractive Tune on it. So much stability. I'm thinking (hoping) the same would happen if he tunes the fork....
 

FarkinRyan

Monkey
Dec 15, 2003
611
192
Pemberton, BC
That thread is an absolute abomination interspersed with moments of pure internet gold. I'm glad that someone has finally dispelled the nonsense about the check valve shim in the Charger at the very least. @slyfink I would say that if you liked the Tractive tune you will likely appreciate the difference that the V-Spec valving will make to the Charger.