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FOX 40 (29) - Grip 1 Damper Upgrade / Improvement

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Discussion starter · #24 ·
Not sure to be honest, but changed something within the shim stack and the valve. I believe this from the parts he returned back with the fork.
 
#26 · (Edited)
Hi,
let me share my experience on grip 1 tuning.
I have fox 34 SC 2022 with grip 1 damper remote; air side at 60psi with no volume spacers; 120mm of travel. Rebound fully open. My weight is lowish at 64kg and do not make jumps or big drops.
Stock: feels harsh and rebound is too slow. Remote lock is stone hard. Not able to use more than 80% of travel; sag at 25%
1st tune:
  • base valve from valve face: 8x6x0.1 + 2x 13.6x6x0.1 + 12x6x0.1 + 8x6x0.1; (stock was 4x 13.6x6x0.1)
  • mid valve: changed the thickness from 0.15 to 0.1mm (this is more than 3 times stifness reduction). I cannot tell the isulated effect from this change, but it alligns (and extrapolates) with the overall trend at fox fork to reduce the midvalve shim stifness.
  • rebound: stock was 5x0.15; changed to 17.25x6x0.15 (face) + 8x6x0.1 + 2x 17.25x6x0.15. Note this stack is now progressive; the target is to have fast recovery from small bumps, but to prevet fast recoil after drops. I am not sure whether the face shim touches the progression shim stack.
  • reclocked the remote dial by 35° in open direction to acheieve less LSC
  • rebound was open at 12clicks from closed (almost fully open). Now, rebound needle adjuster has small effect becasue face shim opens quite easily and provides low resistance oil path.
This tune is much better than the stock - much less harshness, rebound is about right. I can use about 80% of the travel. (I realize air spring progression is too much for me, but no spacers to remove). I tried to reclock the remote dial by ~120° - the LSC was too low and fork was oscilating a lot, while not helping with bigger hits.

2nd tune:
  • base valve from valve face: 8x6x0.1 + 13.6x6x0.1 + 12x6x0.1 + 2x 8x6x0.1 (removed one more 13.6shim). The different diamter of the two shims helps distribute elastic energy in larger volume and decrease stress peaks, and increase fatigue life. I would have choosen lower shim thicknesses to increase fatigue life, but such are not available.
  • reclocked the remote dial by 35° in open direction to acheieve less LSC (same as tune 1)
  • increased pressure to 62psi to imporve mid stroke support
Going through rough rock garden is definetly smoother, due to the decreased HSC from the base shim. Lock is not rock solid due to the lower base shim stack stifness, but OK for my weight. Now I am able to use 90% of travel. I tried running the fork without reclocking the compression dial, but LSC seems to be too much and the fork felt harsh on small bumps, which were not able to bent the base shim stack.

future tunes:
  • add carbon air insert like carbon air. This is expected to reduce progression and reduce adiabatic stiffening from the air spring.
  • base valve: move one of the 8mm spacer shims to the face of the valve. This would mitigate the need to reclock the compression dial afterwards. The expected effect is equal to 36° reclocking. (this change will not allow me to have more LSC by reclocking, if needed)
  • decrease the stifness of the rebound stack. Mostly the LSR by changing the shims to the valve face; I may increase the distance to the HSR shims. I plan to use thinner shims of 0.1mm, to increase fatigue life. I still want to keep the rebound needle adjuster quite open to reduce mid valve compression damping as much as possible; this might be chalanging to achieve from one try.
  • I may increase the float of the mid valve shim by 0.1mm, but do not have the reasoning to do so - compression is fine now.

I am attaching a schema of the changes. I would be happy if this knowedge sharing helps someone. And do not forget this tune is aiming not aggresive, light riders.
Image
 
#27 ·
I have a 2020 49 grip1 on a DH bike I bought used. I liked the fork so much I bought a 2023 40 grip2 for my kenevo to replace the boxxer.

They are so different and I prefer the 49.
49 0 tokens and 70psi.
40 4 tokens and 90psi.

The seller did say he had the 49 tuned but I have no further details on what was done or by who. Same really as I would send the 40 off for the same treatment.
 
#28 ·
mcozzy29 said:
I have a 2020 49 grip1 on a DH bike I bought used. I liked the fork so much I bought a 2023 40 grip2 for my kenevo to replace the boxxer.

They are so different and I prefer the 49.
49 0 tokens and 70psi.
40 4 tokens and 90psi.

The seller did say he had the 49 tuned but I have no further details on what was done or by who. Same really as I would send the 40 off for the same treatment.
Click to expand...
GRIP1 has very little compression damping open and gets really firm as you close it, GRIP2VVC has more compression when fully open but not much when closed.
They are both harsh on sharp edges. Both need modifications to tune up properly.

Stock GRIP feels better riding sedately but gets out of control ridden faster.
Stock GRIP2VVC feels harsher ridden sedately and has a bit more control ridden faster. The HSR/LSR rebound gets most people lost.
 
#29 ·
Made a test with the setup, I described a few posts above. I closed the rebound needle. This has little effect on rebound, as the HSR is low due to the changed shim stack. But, the LSC increased significantly, adding harshness even on small bumps. I start to think the helical spring on the midvalve has too much preload.
 
#32 ·
I opened my grip1 revound assembly. Surprysiling, the valve is not plastic, but metal (maybe metal injection molding). Pushing the midvalve seems it has no hardstop machines in the shaft, but it's travel is limited only by the solid height of the spring. Still not sure, had to pay more attention when it was dissasembled. Anyway I added a copper ring between the valve on the shaft at OD 6mm to raise the valve position and increas the midvalve stroke by 0.2mm. First ride impression is the fork fells much better when going thrugh rockgardens; most noticebly isolating you from high speed impacts.
Image
Image
 
#33 · (Edited)
chehlarov said:
I opened my grip1 revound assembly. Surprysiling, the valve is not plastic, but metal (maybe metal injection molding). Pushing the midvalve seems it has no hardstop machines in the shaft, but it's travel is limited only by the solid height of the spring. Still not sure, had to pay more attention when it was dissasembled. Anyway I added a copper ring between the valve on the shaft at OD 6mm to raise the valve position and increas the midvalve stroke by 0.2mm. First ride impression is the fork fells much better when going thrugh rockgardens; most noticebly isolating you from high speed impacts.
View attachment 2091826 View attachment 2091831
Click to expand...
So you increase the float of your midvalve, I did the opposite but used a 0.1mm thick shim instead of default 0.15mm, resulting in more lsc, less hsc and faster response, not letting any hits go undamped and it feels awesome everywhere. Fox is doing the exact same thing for their new grip x2 and also grip2 2024 tune, but I have even less float than 2024 tune.
 
#34 ·
Jukis said:
So you increase the float of your midvalve, I did the opposite but used a 0.1mm thick shim instead of default 0.15mm, resulting in more lsc, less hsc and faster response, not letting any hits go undamped and it feels awesome everywhere. Fox is doing the exact same thing for their new grip x2 and also grip2 2023 tune, but I have even less float than 2023 tune.
Click to expand...
I think you mean 2024 mid valve stack. So how does your midvalve look? What about the choking that Dougal keeps talking about?
 
#35 ·
dartroom said:
I think you mean 2024 mid valve stack. So how does your midvalve look? What about the choking that Dougal keeps talking about?
Click to expand...
Yes I meant 2024.
The choking happens on high speed hits, so a lot further than where float applies, actually when it floats the curve isnt consistent and the spike can be seen in simulation. But really you just need to use a thin enough oil for these dampers to work, just like you can see Fox changed to a thinner, higher VI oil for 2025.

My midvalve has 18x0.1 + 11x0.15 shims instead of 17x0.15mm shim, so I have 0.1mm less float
 
#36 ·
To clarify, I already have changed the mid valve from 17.35x0.15 to 16.6x0.10 to decrease HSC. The last change increased the float by 0.2mm. I am 66kg and aim for less damping.
In one post Dougal clearly says "The midvalve really needs more stroke." (see few posts above for link). I guess, the increase in midvalve stroke, imporves the choking issue. I followed his advice and I am happy with the results.
p.s. On the next service will try to see/measure what is the actual float.
 
#37 ·
The float is 0,35mm stock, so now you have 0,4mm + if you increase it by some other spacers you have 0,6mm.. stroke doesnt mean float.. the midvalve doesnt have enough room to bend open, actually with more float it gives more hsc because of how the shim bends when it collides with the bolt.. I really suggest you to try less float, but first you would need a proper functioning basevalve to go with it. I have sanded my basevalve piston flat and drilled the basevalve bolt to have a real lsc bleed adjuster. Then I put enough spacers to have 6x8mm clamp with 3x 13,6mm shims, its perfect for 75-85kg rider. For your weight I would use only 2x 13,6mm shims.
 
#38 ·
I agree, I should have 0.6mm float, as described.
I cannot understand how the midvalve shim could collide with the bolt, during bending - kindly, could you sketch it?

My basevalve is modified by using (piston side)2x 8x6x0.1 + 2x13.6x6x0.1 + 1x 8x6x0.1. I am using remote lock, which provides very little verical movement (rotation range is about 90°), compared to non remote lever (rotation range ~270°). I need the two 8mm face shims to set the hardstop of the adjuster. The locked position is not hard solid, but enough for me. In open mode LSC is adequate. I agree with you 2x13.6 provides good basevalve damping. I can fine tune the bleed in the different modes, by reclocking the adjuster knob and wire fixation point. So far the two 8mm spacers are OK. It is quite strange why FOX designed the remote and non-remote versions with such big difference in tunability range.
So, you have basically converted the shim preload adjuster to LSC bleed adjuster?
 
#39 ·
I could but I won't. I have already told you too much. I have simulator data on how it collides, but it's not my data. It collides because there is a huge flow and the shim bends a lot.

It's completely different damping on basevalve when you are still using perimeter piston instead of 4 port when piston is sanded flat. Yes my adjuster is now lsc bleed adjuster.
 
#40 ·
Thank you for the input!
Let me try to summarize the effects happening on the mid-valve:

Low shaft speeds
The stock float of 0.35mm is consumed, providing very little (insufficient) damping. During the shim float, the damping isn't consistent and spike can be seen (in simulation). Is the inconsistency due to rotation of the shim (tilting the shim left/right)?
The improvement is to reduce the float. Practical way is to add spacer shims below the main shim.
Is there a way to improve the inconsistency?

High shaft speeds
The float is consumed, the shim bends so much it collides with the bolt. Oil flow gets restricted producing too high HSC. Thinner shim will reduce the HSC to certain extend. How can the HSC be reduced after the shim colision with the bolt?

Very high shaft speeds
The float is consumed, the shim bends so much it collides with the bolt, the piston ports are not large enough to allow enough oil flow. Chocking happens, damping is too high.
How can this HSC be reduced?
 
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