Fox Factory 38 - missing travel

[Mikerb]

Keep in mind the Fox 38 Factory is their top of the range full enduro fork, and not many of us are likely to be riding it as hard as pro riders.
I set SAG as 25% with all compression and rebound open/fast. Thereafter I use factory recommended settings as a start point and adjust until I am happy. If I cannot find the performance I am looking for I then either increase or decrease PSI depending which way I want to go.....only by a few PSI at a time. What SAG I end up with I have no idea!!
If I need to start from scratch and the recommended settings starting point is way off the mark I take a different approach.
Set SAG..........with settings fully open/fast
Set low speed rebound at middle setting...............everything else still open/fast.
Do a short trail run, adjust LSR until it feels right
Set LSC at middle setting.............short trail run.......repeat adjusting LSC up or down as required.

I usually then leave HSC open and HSR at 2/3 open.......................and go ride. I add one or 2 clicks of HSC for rails with drops and jumps but otherwise leave it open.

 

[RickBullotta]

Me again
Being retired and bored shitless I decided to have another play with my forks. Now everytime I check my sag it's at a different psi to get 34mm!
So I have spent an hour or so at different pressure's and tokens to give me some idea of where I need to be with my forks.
The photo might be of some use to you guys?
View attachment 119382

Makes sense. Spring rates with different #'s of tokens don't vary that much for the first 25-30% of travel, which is of course where sag typically is. And I notice (I think?) that your ideal pressures for hitting your sag target are considerably lower than Fox's specs. And Fox's specs are rather silly, because they don't tell you which sag target (15% of 20%) they used, and of course bike geometry and weight balance come into play. I say use what works for you! The one thing I have noticed with most Grip 2 Fox forks though is that they tend to perform better on trails (vs in a bike park) with almost no compression damping (HSC or LSC)

 

[Oakhills]

**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.

Worked for my forks! I didn’t take off the wheel though, just was a lot of work to extend the forks All the same. the Forks were totally sucked down after letting the air out, and when I felt the transfer port become unblocked with that grease, the forks would cycle up and down, rather than staying sucked down. I’m getting the full 160mm travel now and they feel much better!

 

[Planemo]

Any fork sat 6-12 months won’t perform so well. They put in extra grease to ensure there’s some in 12months time.

Evaporating grease? New one on me...

For used forks, I do wonder whether some stick-downs are simply the result of air gradually passing the piston due to wear rather than blocked ports.

 

[irie]

Evaporating grease? New one on me...

Me too.

 

[Evolution Stu]

Worked for my forks! I didn’t take off the wheel though, just was a lot of work to extend the forks All the same. the Forks were totally sucked down after letting the air out, and when I felt the transfer port become unblocked with that grease, the forks would cycle up and down, rather than staying sucked down. I’m getting the full 160mm travel now and they feel much better!

Nice.
Glad my topic was of value to you mate, enjoy it.

 

[Evolution Stu]

Your spending too much time worrying about sag. It doesn't matter other than a check at the end to make sure you are not completely screw up with your settings.

You want the least amount of tokens you can run without bottoming. Remove a token and and air until you don't bottom out. If you don't have any sag, add tokens and reduce psi until you find the sweet spot of compliance and end stroke support.

I tend to prioritize very fast rebound and add compression to help with bottoming vs adding a tokens and getting a harsh ramp.

Its probably worth you rewording that a little pal as the sag is by FAR the most important part of any suspension system.
It simply doesn't work without it.

 

[Shjay]

Me too.

Never said would evaporate, if left for long time will reduce in performance compared to fresh stuff, not by much so their solution is stick more in. Especially as everyone used to complain of no grease or oil on forks things have gone the other way.

 

[Evolution Stu]

Evaporating grease? New one on me...

For used forks, I do wonder whether some stick-downs are simply the result of air gradually passing the piston due to wear rather than blocked ports.

Me too but I was too busy to reply last week.

Air leaking past the seals is definitely a thing, but the idea of the transfer port is that its slightly wider than the top seal and therefore as the top seal wipes past it, any differential pressure quicky equalises.

So if the lower chamber lost pressure, the upper should add it back until its equalised, and vice versa.

The rider would just slowly notice more sag over time as this happens.

 

[irie]

Never said would evaporate, if left for long time will reduce in performance compared to fresh stuff, not by much so their solution is stick more in. Especially as everyone used to complain of no grease or oil on forks things have gone the other way.

You said ...

They put in extra grease to ensure there’s some in 12months time.

... so what happens to the grease so that in 12 months time there might not be enough? Modern synthetic grease does not degrade in static assemblies.

 

[Shjay]

greased with the correct amount of grease, and put the right amount of the right oil in the damper

You don’t even know what the right amount of grease is! It’s just your guess. & you certainly wouldn’t know how much oil to put in the damper. You mean the lowers, see it’s easy to get things wrong!

 

[irie]

You don’t even know what the right amount of grease is! It’s just your guess. & you certainly wouldn’t know how much oil to put in the damper. You mean the lowers, see it’s easy to get things wrong!

Of course I meant the lowers, but you know this of course.

This is what I said:

Decided to do a lower leg service on my new ZEB Ultimate A2 forks. Found far too much grease on the airshaft. Cleaned off all the grease, re-greased with the correct amount of grease, and put the right amount of the right oil in the damper and airshaft sides. Now work very nicely.

And btw, I do happen to know the correct amounts of oil and grease to use for both my Zeb A2 Ultimate forks and my wife's Pike Ultimate Forks, it's written in the RS service instructions and shown in the RS videos.

 

[Alexbn921]

Its probably worth you rewording that a little pal as the sag is by FAR the most important part of any suspension system.
It simply doesn't work without it.

Fork sag can vary by 10% depending on how you measure it. Standing straight up on the pedals vs full attack position. It's one of the last things you should worry.

I tune for bottom out and quality of travel, then look at sag. And yes you need sag.

 

[Cb750stu]

I've never bothered with sag , I always run coil front and rear so if the spring weights feel good I just go with that

 

[Shjay]

Its probably worth you rewording that a little pal as the sag is by FAR the most important part of any suspension system.
It simply doesn't work without it.

It isn’t, sag is important on the Rear shock as it’s a recommendation by the manufacturer for the bike kinematics but sag isn’t so important on forks the other dials are far more important to be set up correctly. You can have sag set up as you think perfectly & it still ride like a bag of spanner’s

 

[Mikerb]

I commented earlier that I believe the viscosity/ overall consistency of grease can change over time and a lot of forks can spend months or even longer unused and in a variety of temperature/humidity environments. That grease is after all captive within a metal tube which is more or less a sealed environment. I doubt any blockage of the transfer port is due to the volume of grease used but rather the consistency of that grease over time.

Lots of data on google describing the decline of "shear stability" of various greases over time.

 

[Evolution Stu]

It isn’t, sag is important on the Rear shock as it’s a recommendation by the manufacturer for the bike kinematics but sag isn’t so important on forks the other dials are far more important to be set up correctly. You can have sag set up as you think perfectly & it still ride like a bag of spanner’s

Sorry, but with all due respect you are wrong.

All sprung suspension systems are designed to work primarily from the sag point. The sag is the only aspect of the setup that enables the spring to be able to react to a negative terrain change and still leave the vehicle in a stable condition.
Most people think of suspension as only absorbing positive terrain changes (that’s what the rest of the travel is for) but negative terrain changes are dealt with into the sag space and those make up around 50% of your movements.
To help explain this to the non technical folk. Imagine riding along a perfectly flat piece of tarmac at high speed and then riding over a 2cm pothole. Your fork should extend into that pothole rapidly, never leaving contact with the tarmac, thus leaving your bars and seat virtually at the height they were in space… that’s its job.

Without sag, your whole bike and you would have dropped down 2cm into the pothole and then as you exited the pothole the positive movement would be absorbed by the spring, leaving you actually lower in space than you started for however long it takes the rebound circuit to ramp you back up.

I stand by my statement that sag is the most important base setting and shouldn’t be overlooked.

 

[Shjay]

Sorry, but with all due respect you are wrong.

All sprung suspension systems are designed to work primarily from the sag point. The sag is the only aspect of the setup that enables the spring to be able to react to a negative terrain change and still leave the vehicle in a stable condition.
Most people think of suspension as only absorbing positive terrain changes (that’s what the rest of the travel is for) but negative terrain changes are dealt with into the sag space and those make up around 50% of your movements.
To help explain this to the non technical folk. Imagine riding along a perfectly flat piece of tarmac at high speed and then riding over a 2cm pothole. Your fork should extend into that pothole rapidly, never leaving contact with the tarmac, thus leaving your bars and seat virtually at the height they were in space… that’s its job.

Without sag, your whole bike and you would have dropped down 2cm into the pothole and then as you exited the pothole the positive movement would be absorbed by the spring, leaving you actually lower in space than you started for however long it takes the rebound circuit to ramp you back up.

I stand by my statement that sag is the most important base setting and shouldn’t be

Sorry, but with all due respect you are wrong.

All sprung suspension systems are designed to work primarily from the sag point. The sag is the only aspect of the setup that enables the spring to be able to react to a negative terrain change and still leave the vehicle in a stable condition.
Most people think of suspension as only absorbing positive terrain changes (that’s what the rest of the travel is for) but negative terrain changes are dealt with into the sag space and those make up around 50% of your movements.
To help explain this to the non technical folk. Imagine riding along a perfectly flat piece of tarmac at high speed and then riding over a 2cm pothole. Your fork should extend into that pothole rapidly, never leaving contact with the tarmac, thus leaving your bars and seat virtually at the height they were in space… that’s its job.

Without sag, your whole bike and you would have dropped down 2cm into the pothole and then as you exited the pothole the positive movement would be absorbed by the spring, leaving you actually lower in space than you started for however long it takes the rebound circuit to ramp you back up.

I stand by my statement that sag is the most important base setting and shouldn’t be overlooked.

That’s rebound not sag ffs you adjust your REBOUND when travelling over rough ground to compensate the movement of the fork & how fast it returns to its original position it’s not SAG

 

[Redders473]

Sag is a good starting point but dynamic sag is what you need to know but you need telemetry to tell you how much your dynamic sag is.

Some forks like ohlins you don't always use the full length of the fork so you may think your not using full travel but you are.

I've ran a zeb on my levo for 6 months and done loads of testing with telemetry and getting that to use full travel has been a LOT of trail and error.

 

[Alexbn921]

Sorry, but with all due respect you are wrong.

All sprung suspension systems are designed to work primarily from the sag point. The sag is the only aspect of the setup that enables the spring to be able to react to a negative terrain change and still leave the vehicle in a stable condition.
Most people think of suspension as only absorbing positive terrain changes (that’s what the rest of the travel is for) but negative terrain changes are dealt with into the sag space and those make up around 50% of your movements.
To help explain this to the non technical folk. Imagine riding along a perfectly flat piece of tarmac at high speed and then riding over a 2cm pothole. Your fork should extend into that pothole rapidly, never leaving contact with the tarmac, thus leaving your bars and seat virtually at the height they were in space… that’s its job.

Without sag, your whole bike and you would have dropped down 2cm into the pothole and then as you exited the pothole the positive movement would be absorbed by the spring, leaving you actually lower in space than you started for however long it takes the rebound circuit to ramp you back up.

I stand by my statement that sag is the most important base setting and shouldn’t be overlooked.

Sag is important. You need it.

But you don't setup your suspension around it. Only after you set the string rate, ramp and damper settings you check to make sure it's in an acceptable range. Then if it's outside a good range you modify the other much more import settings.

Set your sag to X% is easy for a manufacture to say. It gives a ballpark for a starting point. The problem is that people take it as gospel. Having sag is absolutely necessary, but shooting for a arbitrary number is a fools errand.

For example, the steeper your mountain, the less front sag you end up with. If you tried to get to 20% you would never have enough support without a crazy spring ramp. It's also based on riding style and how you use the brakes.

17, 20, 23% on a fork, it doesn't matter as long as it rides good. How do you measure sag? On the pedals, on the seat, attack position? Are you reducing your damping to get the right bounce? There are too many factors for it to be anything but a ballpark, yeah that's about right setting.

I've used telemetry to measure dynamic sag and it's never the same as static sag.

 

[Ark]

I lost 10mm on my zebs and had to go through the whole slowly de/re-pressuring the fork in increments palaver.

what a faff took me about 30 minutes...

Now I have 160mm of stanchion showing instead of 150mm.

I had an annoying sound on each pedal stroke for the past dozen or so rides that I've been trying to narrow down.
I guess it was the sound of negative pressure in the air spring sucking the fork on each pedal stroke.

 

[Evolution Stu]

That’s rebound not sag ffs you adjust your REBOUND when travelling over rough ground to compensate the movement of the fork & how fast it returns to its original position it’s not SAG

No, rebound for a start is in the damper, not the spring.
And that controls the “speed” that the fork can extend. But where is the fork extending too in my example above, (seated, level smooth ground, sudden 20mm pothole)?

It’s extending into what you set as the sag space…
So imagine you had set it with no sag, and your fork is near to or at the top of its stroke, what would happen as you rode into this pothole?

 

[Evolution Stu]

Sag is a good starting point but dynamic sag is what you need to know but you need telemetry to tell you how much your dynamic sag is.

Some forks like ohlins you don't always use the full length of the fork so you may think your not using full travel but you are.

I've ran a zeb on my levo for 6 months and done loads of testing with telemetry and getting that to use full travel has been a LOT of trail and error.

Indeed you do, the problem with telemetry is that it’s only really of true value to you on a one trick pony As that’s all you can set most things up “perfectly” for. For example It would be great to set a vehicle up for just climbing or for just descending tough terrain, as those two disciplines require very different settings, but the riding most of us on this forum are doing requires massive compromise in suspension settings.

I am a massive fan of telemetry, and spend 8hrs a day working with it.

My business tagline is:
”Without data, all you have is an opinion”

 

[Evolution Stu]

Sag is important. You need it.

But you don't setup your suspension around it. Only after you set the string rate, ramp and damper settings you check to make sure it's in an acceptable range. Then if it's outside a good range you modify the other much more import settings.

I've used telemetry to measure dynamic sag and it's never the same as static sag.

Agreed.
My only point here is ”you need it”.

As Shjay said it’s only important on the rear and I didnt want folk to start dialling up the air pressure to the point of virtually no free movement because they read it on one of my topics and nobody challenged it.

 

[Shjay]

Indeed you do, the problem with telemetry is that it’s only really of true value to you on a one trick pony As that’s all you can set most things up “perfectly” for. For example It would be great to set a vehicle up for just climbing or for just descending tough terrain, as those two disciplines require very different settings, but the riding most of us on this forum are doing requires massive compromise in suspension settings.

I am a massive fan of telemetry, and spend 8hrs a day working with it.

My business tagline is:
”Without data, all you have is an opinion”

Sag is important if you know nothing about suspension but most run 10-15% sag. If you ride Loic Bruni’s fork you would think it’s was broken you would struggle to use 40% travel am sure his mechanic knows about sag but is not running 30% like I expect you do. But loci uses all his suspension to its full potential, people get too wrapped up in SAG there are other adjustments on the fork, we all set sag just not as specific as some….

 

[Evolution Stu]

Sag is important if you know nothing about suspension

Sag is important no matter how much you know about suspension.
The fact you made that specific statement shows that you don’t know as much as you think about it.

 

[Shjay]

Sag is important no matter how much you know about suspension.
The fact you made that specific statement shows that you don’t know as much as you think about it.

Thanks but know more than enough about fork suspension! let’s just say my forks will be set up very differently to your forks, mine are for how I like to ride at speed through rocks & roots at chunk, yours maybe for the more mellow bimble neither is right or wrong we all need sag but your a little be too fixated on it, maybe learn also what the other dials on your forks do

 

[Evolution Stu]

Thanks but know more than you on fork suspension

You are very welcome. Have a great day

 

[Evolution Stu]

we all need sag but your a little be too fixated on it, maybe learn also what the other dials on your forks do

**I see you have edited after my reply, so I will reply to your new comment... **

Who's fixated on it?
I only commented on it because "you" said its not so important on a fork. And since then, in between telling me about rebound damping and Loic Brunis dynamic compression ratio you have also just said "we all need sag"...
Only one of us has reversed his stance in this discussion. And its not me...

As for the other settings, well, I adjust, advise and monitor the telemetry on this kind of stuff for a living on motorsport vehicles and they seem to place just fine thanks.

So unless you are going to educate me on how bicycle suspension is different to Ohlins, Bilsein, Eibach, BCRacing etc used on rally and tarmac racing cars (Aside for the sprung/unsprung mass ratio of course) then I guess my knowledge will translate across to Fox etc just fine.

 

[Shjay]

**I see you have edited aftre my reply, so I will reply to your new comment... **

Whos fixated on it?
I only commented on it because "you" said its not so important on a fork. And since then, in between telling me about rebound damping and Loic Brunis dynamic compression ratio you have also just said "we all need sag"...
Only one of us has reversed his stance in this discussion. And its not me...

As for the other settings, well, I adjust, advise and monitor the telemetry on this kind of stuff for a living on motorsport vehicles and they seem to place just fine thanks.

So unless you are going to educate me on how bicycle suspension is different to Ohlins, Bilsein, Eibach, BCRacing etc used on rally and tarmac racing cars (Aside for the sprung/unsprung mass ratio of course) then I guess my knowledge will translate across to Fox etc just fine.

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