Fox Factory 38 - missing travel

[Cb750stu]

Ooh handbags at dawn

 

[Evolution Stu]

I never said we don’t need sag I said all the other settings can be more important you can run the perfect amount of sag & the fork still run poor if you don’t adjust rebound, & low & high speed compression correctly. Rebound is the biggest one that is not setup correctly on most forks. I did used to do all warranty work for BOS suspension so know quite a lot thanks but yes you have yourself a lovely day

Lets agree to disagree on how the argument started then.
Its better for all concerned as arguments make boring reading.

I agree with you on rebound, watching a rally car quickly drop from 200mm clearance to 60mm clearance live on the telematics in a rough section and not recover again until the track smoothes a little is the kind of real world data that shows us the car has way too much rebound damping for the spring rate / vehicle weight combination and needs to be opened up again so the car can recover faster. (saves money on body parts too as these get ripped off when this happens)

We have to deal with for and aft as well as side to side on cars too. Surprising the difference we will run one side to the other on some circuits. (Oval racing is a great, simple example) So bikes just being for and aft feels a little basic, yet in reality its still complex due to the fact the sprung mass is so much more of the overall percentage and the center of gravity changes so damn much. (Due to my crap riding no doubt)

I would guess most MTB riders run the rebound far too closed (slow) as the manufacturers will send them that way as its arguably safer to do so... And in doing so, it feels harsh as it packs down and stays there.

 

[RickBullotta]

While I don't want to jump into the "sag lives matters" debate here, anyone who has setup a dirt bike fork (and shock) knows that it matters quite a bit. But is just one of many tuning characteristics of the suspension, and that the suspension needs to be considered as a whole system if you want optimal performance (mismatched dynamics front and rear can lead to a horrible feeling bike). At the pro level, they're using some pretty advanced telemetry to track what happens (I am an investor in a company called Motion Instruments, along with Greg Minaar and others) and an experienced tech can interpret that data to make whatever mods are needed. Clearly track conditions matter as well - what might be ideal setup for a dry day could be a traction fail for a wet one. We haven't even talked about things like changing shim stacks, tweaking oil/fluid weight, and all of the other things that could be done to change suspension behaviors. It's a black art to some degree.
Anyway, the setup that works is whatever setup that works - and experimentation is key. And personal preferences can lead to very different setups as well. Find a starting point, and make small mods one at a time (and in both directions) as you find your sweet spot. You'll know it when you find it. A well setup bike just "feels" right (though sometimes the stopwatch might disagree).

 

[Shjay]

I would guess most MTB riders run the rebound far too closed (slow) as the manufacturers will send them that way as its arguably safer to do so... And in doing so, it feels harsh as it packs down and stays there.

Yes correct majority run it too slow!! Setup starting point 2/3rds open if 18 clicks then start 12 & fine tune from there

 

[DaveG01]

F*ck me, this thread is full of keyboard worriers (didn't mean warriors)

 

[Evolution Stu]

F*ck me, this thread is full of keyboard worriers (didn't mean warriors)

I wouldn’t worry about it pal.

 

[Dano78]

**Update - Fixed **
Decided to nip home at lunch and have a play with it as it was bugging me.
And its now fixed.

Since this might be of interest to other owners of any fork, I will detail the procedure I used here:

Step 1: Depressurise the fork slowly whilst equalising as you go down.
Step 2: Remove the air cap completely.
Step 3: Remove wheel and refit axle.
Step 4: Stand on axle and pull up hard, to extend the fork as far and as fast as you can multiple times.

The theory is, the huge depression caused in the lower chamber will suck through any grease blocking the transfer port.
I certainly didn't hear anything happen, but i was huffing and puffing as its hard to pull up against the depression there

I then repressurised as normal and found the fork hits full extension about 75psi now.
Happy days.

Thank you I'm having the same issue as you will give this a try

 

[steve_sordy]

Just found this thread searching for "lost 10mm travel on my Fox 38".
I will get back out to the garage and follow what @Evolution Stu recommended.

Step 1: Depressurise the fork slowly whilst equalising as you go down.
Step 2: Remove the air cap completely.
Step 3: Remove wheel and refit axle.
Step 4: Stand on axle and pull up hard, to extend the fork as far and as fast as you can multiple times.

 

[steve_sordy]

Just found this thread searching for "lost 10mm travel on my Fox 38".
I will get back out to the garage and follow what @Evolution Stu recommended.

Step 1: Depressurise the fork slowly whilst equalising as you go down.
Step 2: Remove the air cap completely.
Step 3: Remove wheel and refit axle.
Step 4: Stand on axle and pull up hard, to extend the fork as far and as fast as you can multiple times.

I did all that and heard the squelching/sucking sound but only once. After that the compression and pull up felt a lot looser and easier. Great stuff! I reassembled and inflated the fork in stages as required. No change, still got the lost travel!!

The fork has been serviced by TFTuned twice, the last time 384 miles ago. Suggestions?

 

[ebikerider]

I did all that and heard the squelching/sucking sound but only once. After that the compression and pull up felt a lot looser and easier. Great stuff! I reassembled and inflated the fork in stages as required. No change, still got the lost travel!!

The fork has been serviced by TFTuned twice, the last time 384 miles ago. Suggestions?

Zip tie down the stanchion to release excess negative pressure. Google it.

And/or get it serviced again.

Why did the internet start my day with this thread ffs. So much crap in it. Disappearing grease.....blocked transfer ports....stop it.....just stop it

 

[steve_sordy]

Thanks @ebikerider. The fork is a Fox 38 and it has the pressure relief valves on the lowers that are supposed to obviate the need for the zip tie trick. But it's so easy to do I might as well give it a go, it worked on a Pike 5-6 years ago.

 

[steve_sordy]

As I suspected, the zip tie trick had no effect, as the pressure relief valves are supposed to negate the need for that. So, I had another go at the deflation, wheel off, yank up and down technique.

No squelching noise this time (did it last time), but when the fork was fully compressed, I pressed the pressure relief valves on the fork. To my surprise, they let out quite a hiss! I repeated the yanking up and down several times, and pressed the valves a couple of times at either end of the stroke until I got no hisses. That must have had an effect I thought and it was with some anticipation that I reassembled the bike and pressurised the fork.

No effect! The fork is still sucked down by the same amount.

 

[steve_sordy]

I took the bike to my LBS and the top guy agreed that it shouldn't be doing that. It had only been about 400 miles since the last service by TF Tuned. He spoke to them and they agreed to take a look at it. It came back having been given a full service. Their written report said that everything was in good condition and working as it should. They did not make any comment about the lost travel. They had set it up with 100psi and changed all my suspension settings. (they had "set it up for me" - but without knowing anything about me). And no charge. All very nice of them. But as I demonstrated to the LBS guy, with respect to the lost travel, nothing had changed! I compressed the fork a few times and let it settle. It pulled up 10-12mm.

The LBS guy is on hols next week, but when he gets back, he will have a chat with Adam at TFT. I want to know whether this is "lost travel", "stiction" or something else. Nobody I have spoken to, read on here, or elsewhere on the 'net has suggested that this lost travel is anything other than a fault. Nobody has said it is "normal". (Edit: @robbydobs said it was normal three and a half years ago, but nobody agreed with him and some said that Fox 38's were different.....)

Meanwhile I will be riding the bike. I will get back to you.

 

[Bones]

Mine actually had a faulty air damper so all my earlier comments are about a faulty fork!
But the fact is that the forks will sag under the weight of the bike if you don't have at least 100psi in them to counteract the battery and motor weight. I have always had to lift my front wheel off the ground when measuring sag.
To me 10mm or so is normal unless you have a shit load of air to hold it up.

 

[Mikerb]

Mine actually had a faulty air damper so all my earlier comments are about a faulty fork!
But the fact is that the forks will sag under the weight of the bike if you don't have at least 100psi in them to counteract the battery and motor weight. I have always had to lift my front wheel off the ground when measuring sag.
To me 10mm or so is normal unless you have a shit load of air to hold it up.

I think it does have to do with the air pressure although not sure it necessarilly needs "a shit load"! If you use tokens/spacers it reduces the volume of air and therefore invariably leads to setting a lower air pressure. That is likely to allow the fork to settle rather more just under the weight of the bike ...........and that will also depend on the geo of the bike, for example how much of the bike weight is forward of the BB.
It might also be worth measuring the total stancion length to see if the fork is nevertheless allowing the 150/160mm travel or not.
I have 2 Fox 38 forks. A 160mm non ebike fork and 180mm ebike tuned fork .....both settle a bout 6 under bike weight but when I pull them up the 160mm fork is 164mm from seal to crown and the 180mm is 180mm!!

Try setting the fork up with fewer or no tokens??

 

[steve_sordy]

@Bones I suppose so. Let's do some very simple sums.

Let's assume that the bike weighs 24kg and the rider weighs 96kg, total 120kg. Let's also assume that the weight is evenly distributed between front and rear wheels, for starters

Later Edit: The bit I missed is that the front wheel and half the fork is unsprung. Let's assume that bit weighs 4kg

So 12kg 8kg of bike weight on the front wheel and 48kg of rider.

If 12kg 8kg of bike weight generates 10mm of travel, then another 48kg should add another 40mm 60mm. Yes, I know that air springs are not linear, but another 40mm 60mm seems is a lot. Especially when setting the fork, I move my weight forward from the central position to get my target fork sag. Anyway, staying in the central position that's 50mm 70mm on a 160mm fork, ie 31% Not too bad! 44% dreadful!

But once I move my weight forward, the fork will sag more.

I am not too concerned about the measured sag, whether I should pull the fork brace upwards or not. I set the target sag and then ride the bike before adjusting pressure up or down according to how it feels. I know it's an iterative process involving changes to the suspension settings other than air pressure, but eventually I become happy.

But what I can't avoid is that others have fixed the missing travel problem by a variety of methods (zip ties, furious riding, deflating and jerking the fork......). I too have fixed lost travel on previous forks (a Pike actually) with the zip tie trick. And none of those bikes exhibited lost travel once fixed.

I can't help feeling that the fork is not working the way it should. It will niggle away at me until I either get a convincing answer that will not only satisfy me, but others on this Forum. I want to be able to say to someone when they report lost travel that it is either definitely a fault that is fixable in a certain way, or it is not a fault and needs no action. It can't be normal, yet be fixable.

The other point to mention is that the missing travel was 10mm when I had 60psi in the fork and it is still 10mm with 100psi and after a TF Tuned service. If it was a "normal" sag under bike weight then I would have expected the missing travel to have reduced to about 6mm. It didn't.

 

[steve_sordy]

I think it does have to do with the air pressure although not sure it necessarilly needs "a shit load"! If you use tokens/spacers it reduces the volume of air and therefore invariably leads to setting a lower air pressure. That is likely to allow the fork to settle rather more just under the weight of the bike ...........and that will also depend on the geo of the bike, for example how much of the bike weight is forward of the BB.
It might also be worth measuring the total stancion length to see if the fork is nevertheless allowing the 150/160mm travel or not.
I have 2 Fox 38 forks. A 160mm non ebike fork and 180mm ebike tuned fork .....both settle a bout 6 under bike weight but when I pull them up the 160mm fork is 164mm from seal to crown and the 180mm is 180mm!!

Try setting the fork up with fewer or no tokens??

I will measure the stanchions.

 

[Mikerb]

I will measure the stanchions.

your fork will compress quite easilly at the top of its travel because as you said air pressure is progressive not linear. The more plush your fork at the top of its travel the easier it will settle under bike weight. If the 38 is the Ebike version it also has a damper tune that allows it to be plush at the top of travel but ramp up quickly in mid travel.....more so that the standard tune. Why mention the damper??? The rebound setting also has an impact on SAG which is why it is best to first set airpsring pressure with all compression and rebound settings fully open/fast, and then set rebound ( still with compression settings fully open). It is likely the air spring will need more air pressure the slower you set rebound so it is a balance. Unlike RS forks which I find easier to set up,, it has been my experience the Fox 38 is sensitive to the balance between damper settings and air spring settings.

So another thing you could try is setting you rebound to full fast (initially) to see what impact that has.

An unrelated point maybe............when setting sag I think it best to be in the ready position up on the pedals. Depending on the reach etc of the bike that may or may not have your chin over the stem but the important thing is ( in my opinion) if that is how you position yourself when riding up on the pedals, so that is how you should set SAG.........ie dont lean further forward over the bars. Any average reach coupled with less that 66 degree head angle will already have you forward enough.

 

[steve_sordy]

....................
An unrelated point maybe............when setting sag I think it best to be in the ready position up on the pedals. Depending on the reach etc of the bike that may or may not have your chin over the stem but the important thing is ( in my opinion) if that is how you position yourself when riding up on the pedals, so that is how you should set SAG.........ie dont lean further forward over the bars. Any average reach coupled with less that 66 degree head angle will already have you forward enough.

I agree with that @Mikerb it's how I do it normally. As for set up I will try the settings from TF Tuned (just in case) and then start from scratch again. which will be pretty much what you recommended anyway.

 

[Bones]

I still reckon you don't have enough air pressure in your forks.
You say 30% sag, but fox recommends between 15 and 20% sag as that's what they are designed for.
If they are ok at 100 PSI on a Dyno without the gravity effect of an ebike on them. Then it suggests more air is needed than you are running.
May I suggest that you stick about 120 psi in them and see if they are fully extended. Then start dropping pressure to the recommended 15% and see what they ride like. Assuming 120 is enough.
They might be awful for you but if there's no lost travel then they are working as designed.

 

[steve_sordy]

I still reckon you don't have enough air pressure in your forks.
You say 30% sag, but fox recommends between 15 and 20% sag as that's what they are designed for.
If they are ok at 100 PSI on a Dyno without the gravity effect of an ebike on them. Then it suggests more air is needed than you are running.
May I suggest that you stick about 120 psi in them and see if they are fully extended. Then start dropping pressure to the recommended 15% and see what they ride like. Assuming 120 is enough.
They might be awful for you but if there's no lost travel then they are working as designed.

I will try anything. When I first got it, I set up the fork according to the Fox recommendations and it felt awful. It was like riding over broken bricks the whole time (big ones). So I slowly changed the settings.

When I compared the settings that TF Tuned set up for me (how the hell do they know me?), they weren't that far away from what I have anyway, apart from the air pressure. I will be giving that a go on my next ride.

Good idea to see how high the pressure has to be to get full extension.

 

[Bones]

I will try anything. When I first got it, I set up the fork according to the Fox recommendations and it felt awful. It was like riding over broken bricks the whole time (big ones). So I slowly changed the settings.

When I compared the settings that TF Tuned set up for me (how the hell do they know me?), they weren't that far away from what I have anyway, apart from the air pressure. I will be giving that a go on my next ride.

Good idea to see how high the pressure has to be to get full extension.

I have mine at 110 psi for 82kg and that gives me 35mm sag. Which is 20%. HSC and LSC open.
If I run them at 95 psi it makes a softer fork but I have to have HSR fully open because I've not enough air pressure to bring the forks back up and it ends up a harsh ride and I loose that 10mm from the travel.
That's with a factory tune, but that only effects the damping.

 

[RickBullotta]

I will try anything. When I first got it, I set up the fork according to the Fox recommendations and it felt awful. It was like riding over broken bricks the whole time (big ones). So I slowly changed the settings.

When I compared the settings that TF Tuned set up for me (how the hell do they know me?), they weren't that far away from what I have anyway, apart from the air pressure. I will be giving that a go on my next ride.

Good idea to see how high the pressure has to be to get full extension.

In any case, open both compression circuits all the way (zero compression damping) and go from there.