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Anyone changed the oils in a Fox Fit 4 damper for a lighter oil? I'm very light and find the damper too harsh in colder temperatures. They're fine in the summer with the compression fully open. I think they have 5wt oil as standard and wondering how much lighter I could go.
I had an older (2016) fit4 36 retuned by TF for my then <70kg weight, it transformed the fork. I spoke to them about just using a lighter oil, and they said it could have some undesired consequences without a reshim as well, so recommended it being much better to do the shim stack anyways. I reckon it's the best £150 odd I've ever spent on suspension.
Different types of damper behave differently with oil weight changes vs changes to the damper. e.g. shim stacks are less dependent on oil weight than orifice ports / needle valves.
It might work, and it's cheap to try. I'd be inclined to give it a go and see if it works for you.
Anyone know the simplest way to change the oil? Or at least remove some of the stock 4wt and add in some 2.5wt.
I've just changed the damper oil in my fox 38 grip 2 forks.
It had the 5wt Teflon oil in it and now fox use motorex 4wt oil.
I had to disassemble the damper assembly in order to do a complete change over.
Not for the faint hearted if you've never done them before.
I've got an older fit4 in mine, jtech fitted the andreani piston kit they offer for me and it did "unchoke" the damper usefully, I understand it's not as big a change for newer forks as Fox basically made some similiar changes.
But it was still quite damped, because I weigh nowt, and switching to 3wt has been great for me. Maybe it's just a little bit too far, I will probably switch to a 4wt mix, but the novelty of actually having adjustable damping that I don't pretty much roll all the way off has been great. So many forks just don't deal well with people on the end of the weight scale.
As others say it's cheap to do and fairly easy on most forks so it's pretty much always worth experimenting.
Not a FIT4, but have had 3W in a GRIP2 a couple of times, and just put 2.5W in a GRIP damper...
It's not difficult... Just need a shaft clamp for the damper tube. Fork lowers off, remove the damper from the CSU, damper in the shaft clamps in the vice, unscrew the compression assembly, drain old oil and cycle the rebound rod several times to make sure it's fully drained, back in the vice clamps, refill with desired oil to around 50mm below bleed hole, cycle rebound rod a few times, fill oil up to the bleed hole, cycle rebound rod a few more times, top up oil to bleed hole again, refit the compression assembly carefully, refit damper to the CSU, lowers back on the forks, squirt correct amount (and weight, making sure damper side is the same oil as you've just used to fill the damper) of oil into the lowers before then pushing them all the way on and tightening up the bottom nuts...
I'm 92kg so more like 95-96 ready to ride, and almost every Fox damper ever has been overdamped from stock even for me!
The 2.5W in the GRIP damper is a revelation! First ride this morning, doesn't choke under compression any more and I can actually use the compression adjust lever (found half way round is ideal as stops a fair bit of low speed dive) and the rebound adjust is still very useable without reshimming the rebound stack. I thought for the price of some shaft clamps off ebay (£15) I'd give it a go before stumping up for a GRIP2 or GRIPX2 damper (both of which I know I can get the setting I want from, albeit with a lighter than stock oil)... Consider me impressed enough (for now at least) that I will be rocking the basic GRIP damper for a while longer...
It had the 5wt Teflon oil in it and now fox use motorex 4wt oil.
From memory, Fox 5wt and Motorex 4wt (which is basically what Fox use now instead) are almost identical cst rating wise... I'm sure new oil will have made a difference over old oil, but if you want a meaningful change, drop to a 2.5W oil and the compression adjusters will become much more useful!
But it was still quite damped, because I weigh nowt, and switching to 3wt has been great for me. Maybe it's just a little bit too far, I will probably switch to a 4wt mix,
At your weight, you could switch to water... 😂 You'd certainly be better off still with 2.5W over 3 or 4...
So many forks just don't deal well with people on the end of the weight scale.
Fox make some great products, but for longer than I can remember, if your name wasn't Jared Graves or Richie Rude then the stock tune would be WAY too harsh for you regardless...
The Grip is a perfect example, it's really pretty good <if> it works for you but it just doesn't work for either really small or big people. But it's also targeted mostly as an OEM part so loads of people end up with a damper that doesn't work for them and is tricky to make better without throwing cash around. Sucks tbh
The 2.5W in the GRIP damper is a revelation! First ride this morning, doesn't choke under compression any more and I can actually use the compression adjust lever (found half way round is ideal as stops a fair bit of low speed dive) and the rebound adjust is still very useable without reshimming the rebound stack.
Is this a 38 or 36?
I am 79kg and find this is the case on my 38 Performance anyway, I run the compression a bit over halfway closed most of the time and it doesn't choke/spike/feel harsh.
But another recent thread on here seemed to suggest my fork may not be typical. Perhaps I got one with a bit looser bushings or something.
Sorry for the tangent, I've just been intrigued that it doesn't ride how the internet led me to expect.
The Grip is a perfect example, it's really pretty good <if> it works for you but it just doesn't work for either really small or big people. But it's also targeted mostly as an OEM part so loads of people end up with a damper that doesn't work for them and is tricky to make better without throwing cash around. Sucks tbh
A little knowledge (and there's a lot of it on t'internet if you look for it) goes a long way though... It's a super easy damper to work on... Shaft clamps for it were £15 off ebay, a chamferless 28mm socket is about £10 typically, and that was all the dedicated tools needed to work on it...
I do agree with you that due to it trying to be all things to all people, there's a lot of people out there riding on them in a completely unsuitable tune... But as I've just proven to myself, it really isn't difficult or expensive to make it work a whole lot better for yourself IF you're prepared to accept some limitations compared to throwing in a more expensive damper (lack of HS/LS separation on both compression and rebound for instance)...
Is this a 38 or 36?
I am 79kg and find this is the case on my 38 Performance anyway, I run the compression a bit over halfway closed most of the time and it doesn't choke/spike/feel harsh.
But another recent thread on here seemed to suggest my fork may not be typical. Perhaps I got one with a bit looser bushings or something.
Sorry for the tangent, I've just been intrigued that it doesn't ride how the internet led me to expect.
Good point well made... This was on one of the £250 "paint damage" special 36's from Merlin Cycles... My experience of 38's with this damper actually mirrors yours, albeit I've only ridden E-Tuned versions so can't compared directly...
My experience so far of 36's vs 38's, both with this damper and in general, is as follows...
38's tend to have quite a bit tighter bushings than 36's from what I've seen/felt, obviously there will be exceptions, but that's been the general rule. In fact I had one 38 that the bushings were so tight from the factory that even with barely any rebound dialled in for my 95kg riding weight, it still wouldn't rebound quick enough on repeated hits! A bushing hone makes a huge difference on a 38 typically, less so on a 36... The 38's on my eBike were "pretty good" as far as 38's go the guys @ Sprung said (Zeb's are horrendous apparently stock!), but were still causing quite a lot of stiction until they were correctly honed. Took my 36's apart myself and was ready to run the lowers down to Sprung to hone the bushes, but to be honest, they felt good enough not to bother.
The 38 GRIP damper (at least in the E-Tuned versions) does seem to behave as you've suggested, it doesn't spike as much and you can actually use the lever as a compression dial, where even fully open a stock GRIP damper on a 36 I get compression spikes through my hands (95kg riding weight remember!!!). I couldn't tell you what internal differences there are, or if the E-Tune itself is responsible though. The one thing I will say is that though it feels better "stock" than the GRIP in a 36, it still doesn't offer enough damping support as I'd like without introducing spiking... I added a GRIPX2 to my 38 and it's superb (though not cheap obviously!).
The 36 chassis is noticeably flexier having spent time on 38's... We all got used to 36's being stiff and bombproof some years ago, 38's have changed this (at an obvious weight penalty), and I have to say that I agree with Fox as to where they now aim both forks at the market... In fact, as a heavier than average rider, I wouldn't want to run a 36 @ 160mm travel and would run a 38 at that travel instead (and am doing), keeping a 36 for 150 or shorter... Lighter riders will I'm sure still be fine with a 36 @ 160mm travel.
Speaking of chassis flex in 36's... I picked up a 150mm "Glidecore" NA3 airshaft off ebay cheap last week, just to see what the hype was about... OMG WOW!!! I had wondered if it was a bit of a triumph of marketing over substance, but no it absolutely is not! The fork is WAY more active when you're actually pushing it hard, and recovers far more quickly as a result... Last 2 rides, I've had at least 3 front end slides on each ride that would have resulted in me lowsiding and eating dirt as my front tyre lost grip leant quite hard over, and in each case the fork recovered (deep in its travel and banked over, so chassis twisted) just like it would with no side load and my front tyre recovered grip and I rode it out! It was quite surprising being able to push so hard on the front tyre like that, to find the limit, but then for the fork to bring you back from it without eating dirt! I suspect my air pressure was a touch low (seems you need to run 5-10% more air in the fork with the NA3 shaft) hence causing the slides in the first place (that and a new bike I'm still getting used to), but the way which the fork recovered was impressive!
FWIW my £250 Merlin Special Fox 36 with 2.5W oil in the damper, an NA3 air shaft and a Diaz Runt air cartridge would absolutely destroy any previous generation off the shelf Fox 36 Factory fork performance wise at 150mm travel on a trail bike... Would it be even better still with a GRIPX2 damper? Of course it would, but I'd suggest that's not as important as the other steps on a mid travel fork at least... For a longer travel fork, then yes absolutely you want the larger stanchions of a 38 and a damper with separate low/high speed damping controls.
For a longer travel fork, then yes absolutely you want the larger stanchions of a 38
It depends. It's more about the rider than the travel I suspect. The loss of a 170mm 36 for lighter riders is a shame.
and a damper with separate low/high speed damping controls.
Truth.
But shorter travel, the simple Grip damper, with the sweep compression dial ran fully open for most folks, is still a brilliant option.
Cheers for the detailed response Mboy - I suspect I'm in the sweet spot for the Grip damper as an average weight, average speed rider.
I've not been on a Fox fork for years and I'm pleasantly surprised TBH. No mods needed on mine, but I will swap in my Zeb Ultimate (with Trutune) at some point to see how it compares.
I also grabbed one of those £250 36s, it's waiting to go on one of my trail bikes if I can't get a spring rate that works for me on my Z1 coil.
The loss of a 170mm 36 for lighter riders is a shame.
Same with the Lyrik eh.
I have a 38 PE. It's brilliant, as long as I don't touch LSR (more than about 2 from open). That somehow turns the whole damper to shit.
Maybe something different but similarly weird happens with other fox models?
I have a 38 PE. It's brilliant, as long as I don't touch LSR (more than about 2 from open). That somehow turns the whole damper to shit.
Thats just the typical Fox 38 problem of tight bushings… Get them serviced and bushings honed to tolerance, and be amazed at just how good the fork is once manufacturing tolerances are dealt with (on a £1200 fork… Yes really!!!)…
Nah, just run it open and get on with riding.
Well, in this case it costs money to find out... so save the money and just ride the fork as is. When it comes to a service... as an add on, it could well be worth it.
Same with glidecore. Small gains. Might be worth it. Probably not a necessary spend. Oh, suspicious that there's still no glidecore for the 38... and Fox have done a "same old fork, new colour" update to the 38 this month... how far off is a properly updated 38 still...? Surely it's the longer travel forks that glidecore could make the most difference to?
Just as an aside, Slick and Slide do a bushing sizing check as part of a service - I asked before I sent my Zeb in 🙂
He didn't mention that they were particularly tight, but I think it was the air spring that was the "problem" anyway, as the fork worked sooo much better with a Trutune widget to tweak that.
Sorry, bit of a tangent again.
Thats just the typical Fox 38 problem of tight bushings… Get them serviced and bushings honed to tolerance, and be amazed at just how good the fork is once manufacturing tolerances are dealt with
@mboy Fair enough ... though please can you explain why LSR (soz, typed LSC initially) affects the fork but nothing else does? I'm not a suspension guru by any stretch but it feels unlikely to me
I had an older (2016) fit4 36 retuned by TF for my then <70kg weight, it transformed the fork. I spoke to them about just using a lighter oil, and they said it could have some undesired consequences without a reshim as well, so recommended it being much better to do the shim stack anyways. I reckon it's the best £150 odd I've ever spent on suspension.
Same here on a 2022 36. The minute I said to TF Tuned I was 68kg and the fork felt chattery/harsh they knew what to do. I also bought oneup bars that improved the front end even more
@mboy Fair enough ... though please can you explain why LSR (soz, typed LSC initially) affects the fork but nothing else does? I'm not a suspension guru by any stretch but it feels unlikely to me
OK... You're familiar with the difference in HS and LS damping I take it?
Well simply put, tight bushings are adding a load of friction damping to your fork... Both LSC and LSR will be affected, but it will be more noticeable in the rebound damping circuit than the compression, because if anything you're likely to run little or no compression damping unless you blow through your travel too easily, when you might actually add a little. When you get your bushings resized, you'll be able to set your LSR where you would expect to need it, but you'll also be surprised that you need to add quite a few clicks of LSC too owing to the fact that you now have a lot less friction in the fork...
So what's happening is that the fork isn't extending as quickly as it should do in the low speed rebound events because of the extra friction. High speed events won't really be affected too much, the forces involved are much greater in a high speed event and hence the friction forces from tight bushings will be a much lower % of the overall damping force compared to the low speed events.
Tight bushings really manifest themselves as a fork's inability to recover grip in a corner say, or the feeling of packing down over repeated hits. So you reduce the clicks on the LSR damper to compensate, and it starts to feel better, but the problem is that the friction damping from tight bushings is very inconsistent (it can be WAY higher when the fork is side loaded for instance, and also why Glidecore is going to be quite a big thing!) which is highly undesirable... The fork can feel fine when rebounding over bumps that don't side load the fork, but will rebound FAR slower for a given damping setting when side loaded because of the extra friction from the tight bushings.
Basically, friction between the bushings and the stanchions in a suspension fork is the enemy of consistent performance... Likewise friction in an air spring system is not ideal, and why coil springs offer inherent benefits here but also why there's been such continual efforts to reduce friction in air spring systems given the weight and tunability benefits that they bring to an MTB suspension system too... Remove the friction, the more you can get the damper doing what it should be doing and consistently controlling the performance of your fork...
Just as an aside, Slick and Slide do a bushing sizing check as part of a service - I asked before I sent my Zeb in
He didn't mention that they were particularly tight, but I think it was the air spring that was the "problem" anyway, as the fork worked sooo much better with a Trutune widget to tweak that.
Sorry, bit of a tangent again.
Great stuff... The air spring issue is one of the manufacturers putting WAY too much grease on the piston during assembly (it really only needs a little), and the grease then blocking the transfer port, which then leads to the fork packing down into its travel, compounding the lack of recovery over repeated hits... The fact this is considered normal for £1k+ suspension forks and manufacturers don't bat an eyelid that their QC is absolutely dogshit here, is incredible! Fortunately there's quite a few good suspension tuners out there now that know what they're doing, and for about 10% of the retail value of the fork can actually get it working like it should do in the first place!!!
Well, in this case it costs money to find out... so save the money and just ride the fork as is. When it comes to a service... as an add on, it could well be worth it.
It never ceases to amaze me that people will spend £thousands on bling carbon wheels and other trinkets that don't actually add any performance to their bike (in fact, can often detract from it), but won't spend £100 or so on actually getting their suspension to work as it should... OK, so I agree, it should work well from the factory and you shouldn't need to spend that £100 or so on it, but the reality is that it doesn't, and as performance per £ ratios go, getting your stock forks stripped, bushings honed and everything setup to you as an individual, is by far the best money you will ever spend on your bike!
Same with glidecore. Small gains. Might be worth it. Probably not a necessary spend. Oh, suspicious that there's still no glidecore for the 38... and Fox have done a "same old fork, new colour" update to the 38 this month... how far off is a properly updated 38 still...? Surely it's the longer travel forks that glidecore could make the most difference to?
I'll give it to Fox, they know how to price things so that they are hard to justify experimenting with to see what the benefits might be... I was lucky, I scored a brand new Glidecore shaft on ebay out of a fork that the owner changed up from 150 to 160 from new, and it cost me £50 (RRP on these shafts is £140!!!)... But by christ, does it work!
As for why it hasn't been rolled out to 38's... Well I had a good think about this last night as it happens... And I think there's 2 big reasons that it hasn't been so far and one smaller reason as to why it would be far less effective for a 38 than on a 36... They are as such...
-Firstly, the 38 chassis is FAR stiffer than the 36 chassis, and Glidecore is aimed at reducing friction in the air spring due to fork chassis deflection, something the 38 doesn't suffer with to anywhere near the same extent.
-Secondly... The 38 air spring is a separate cartridge unit, it doesn't rely on the air shaft piston maintaining a good seal with the inside of the fork stanchion like a 36, there's more tolerance built into the system in the first place...
-Thirdly... The 38 runs higher pressures for a given rider weight, owing to its smaller air piston displacement (34 sized, inside a separate air chamber unit independent of the inside of the fork stanchion), and as I mentioned above when talking about how friction affects LS damping much more than it affects HS damping events, the higher pressures inside a 38 mean they're less affected by friction than the 36, which compounds my first point here too...
Does that mean that Glidecore for 38's isn't on the Horizon?!?! I honestly couldn't tell you, I don't work for Fox... I suspect if and when it does come, there'll be all sorts of huge claims about it and how well it works too. But the reality is that given the architecture of the 38 vs the 36, it would make far less difference in a 38 than it does inside a 36, where my first 2 rides on it have been really quite a revelation to the point of "why didn't they come up with this before" being the main question on my mind...
Thanks mboy - kinda makes sense, though I doubt it's all due to packing down in my case
I'm away on holiday currently and for some reason can't log in while on my phone, so only brief periods when I can connect the laptop & actually post replies.
While I was googling yesterday I did find some comments on pinkbike that seem to echo my experience re LSR. Poster seems to own a suspension business in NZ but may be a bullshitter pretending to know what they're on about instead. Talks about needing to machine out some of the valving 😮 😬
I found this from the front page article. You're completely correct in your observations. The GRIP2VVC damper used in the F38 is harsh and lacks support. The harshness comes from the mid-valve choking. This gets worse the more you close the LSR dial as the LSR ports are a significant oil flow path during compression.
The total compression damping available is low even with HSC and LSC fully closed. But the harshness from the mid-valve choking leads everyone to run compression more open and try to compensate with more air pressure.To fix it requires significant modifications (i.e. cutting metal and adding new parts). I think I'm the only one worldwide doing this.
https://www.pinkbike.com/forum/listcomments/?threadid=246914
While I was googling yesterday I did find some comments on pinkbike that seem to echo my experience re LSR. Poster seems to own a suspension business in NZ but may be a bullshitter pretending to know what they're on about instead. Talks about needing to machine out some of the valving
I suspect he knows what he's talking about... Certainly I know enough to describe what's going on with your suspension and how to pull it apart and put it back together again, but not enough to know what to do to start modifying internals... I do know people who know that stuff though, so would always ask them for their input before modifying anything (as i did with Jake @ Sprung, before I pulled my cheap 36 apart to tune it)...
I did a few days "work experience" for Tim Flooks way back when he'd only just started TF tuned, and at the time the "Black Box" tune to the original 7" travel Cherry Red Boxxers was all the rage, and he showed me what was involved... To be honest, it was very rudimentary, but did involve removing material from the compression piston (made of plastic, so you had to be careful, though shortly after someone on the aftermarket did come up with an aluminium replacement pre-modded iirc) to stop the compression choking and make the adjuster dials more useable...
Is it necessary though...? That's another question...
To be honest, with the GRIP2 damper, my experience (as someone the wrong side of 90kg at least) has been that with a thinner oil than stock, the compression spiking harshness goes away and you can use the adjusters a little more, albeit I'm actually that rider that prefers to support the fork a little more on the spring than the damping anyway... GRIPX2 seems to have solved this issue internally, though obviously at a significant expense if you're already running a GRIP2 damper, and from speaking to Jake and others I respect in the suspension business, you'll get 99% of the performance of a GRIPX2 damper from a GRIP2 damper with a slightly lighter oil in, and possibly a mess about with the damper shim stack if you're on the lighter side... Something that he can do on an existing fork for a fraction of the price of buying a GRIPX2 damper outright!
Thanks mboy - kinda makes sense, though I doubt it's all due to packing down in my case
Happy to (hopefully) help... It won't all be due to packing down, but I guarantee that if your bushings haven't been resized and the air spring hasn't been opened and all the excess grease removed from stock on your 38's, that the fork will be packing down a LOT regardless of what you do to compensate... Even without messing with the damper, doing these 2 things will yield an enormous performance improvement on a stock Fox 38 that you're experiencing the issues you describe with...
Removing and re(de)greasing the airspring and getting the oil amounts correct makes a huge difference, and is easy to do yourself with only a few tools. Worth getting those tools for lower servicing anyway.
I did a lower leg service and changed the oil in the Fit 4 damper this afternoon. Was quite tricky getting the tiny circlip out the top.
The hard part now is getting all the air bubbles out. The damper is currently held upright in a clamp with a large open top sirynge full of oil. I'd read about massaging the bladder while slowly moving the damper rod up and down and leaving for 30 mins for any air to settle before repeating. Well, I've been doing that since 4pm and still got tiny air bubbles coming up into the sirynge. I've tried opening and closing the compression and adjusting rebound to try and dislodge any remaining air. It did start to feel right with no air then it made a slurp noise and more air came up. I'll leave it as it is overnight and try again before work tomorrow.
Any tips?