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DHX Air Tuning - How to get more mid stroke compression?

Rick205

Monkey
Jun 20, 2006
200
0
Im sorry if this has been posted before, a search found nothing.

My bike came with a DHX air, and i want/need more mid-stroke compression, it bottoms too easily (even with above suggested air pressure) - and im light, and it sits into its mid-stroke too much.

Does anybody know how i can achieve more mid stroke compression?

Oh, and dont just say buy a coil - that is not an option right now.

Rick
 

rosenamedpoop

Turbo Monkey
Feb 27, 2004
1,287
0
just Santa Cruz...
DHX airs inherently lack mid stroke compression damping. Just the way it is with that shock.

But, bottoming-out has little to do with this. You might try turning your bottom-out knob in a bit. Go in stages with this, or you'll have it ramping too sharply at the end and limiting travel.

You also might want to increase your boost psi incrementally as this will effect both compression and rebound.

Also, read the set up guide and owners manual thoroughly!
 

Rick205

Monkey
Jun 20, 2006
200
0
Thanks to the replies, thats a link to my own thread a while ago so im well aware of it :busted:- the grease trick diddnt help much.

I dont have a manual so ill have a look on the fox site, i was wondering if anything can be altered (valving as in a coil shock)

If it is famousley poor in the mid-stroke i wonder why its specced on this frame - with my romic coil over (sold) it was wallowy and blew through mid-stroke too - so the frame design coupled with this characteristic of the shock makes the problem worse.
 

norbar

Turbo Monkey
Jun 7, 2007
9,554
339
Warsaw :/
Rick does it bottom out on jumps only or also while riding? Cuz I didn't feel it that much on mine lapierre. It felt linear in the middle but the progression in the last part of the stroke saved my ass every time. I'm starting to worry cuz I didn't to much hard riding on it yet.
 

Rick205

Monkey
Jun 20, 2006
200
0
Just jumps/ drops and hard compressions.

The harder i ride the worse it feels to be honest - when not pusing on its great, very plush etc.

I think im going to get a coil in the future and get it tuned for more midstroke compression by mojo or someone.
 

norbar

Turbo Monkey
Jun 7, 2007
9,554
339
Warsaw :/
hmm on mtbr there was some talk about replacing the canister with an rp23 but I don't have acces to rp23 and I'm scared of doing that(and I don't know how the shock feels on hard stuff for me).

But if you wanted to change manitou evolver air seems to have much better mid stroke.
 

jamesdc

Monkey
May 6, 2007
469
0
heres the solution,









Buy a coil shock, sorry man, its a common problem with dhx airs, you can up the air pressure more but then it isn't as sensitive, I could never find a solution on the one I was running so I just ran it too stiff. I'd replace it with a coil when you can.
 

pelo

Monkey
Jun 11, 2007
708
0
I removed a shim and added pressure on my RP23, I had about the same problem. I´ve never had a DHX air, but I like to share my experiences.
It works how I like it now.
 

frorider

Monkey
Jul 21, 2004
958
6
cali
get a piggyback roco air WC or TST. i have only one ride on mine (had some fork warranty issues recently) but so far it appears not to blow thru the mid stroke like the dhx airs (including mine) are famous for doing. maybe others have more time on their piggyback roco airs and can give some useful info.
 
Oct 8, 2003
202
0
I have heard people who had problems with this and mine did seem to be a little light in the mid stroke compression when I first got it and all I did was put the bottom out adjuster in (just past the second line so only one line is showing) and this took care of all my mid stroke problems. It is pretty stiff at the end of the travel but I prefer it to be kind of stiff then kind of soft (since this is not my race bike it is on) I have this on my specialized enduro and with 190 PSI in the air chamber (boost pressure is not adjustable on the enduro's 5.0 the valve would hit the frame so it is filled to a set amount and plugged off) and the bottom out where I said it is. It rides plush and pedals really well. The thing about air shocks is that they ramp up naturally so I can honestly say I have never felt mine bottom out and I have been using my enduro for DH while waiting for my new DH bike to come and I have hit plenty of large drops at least 10ft with no issue. The leverage ratio on the enduro is pretty low 2.4:1, it has a 2.5 in stroke and 6 inches of travel. depending on your bike if it has a high leverage ratio this could have alot to do with your problem and there may not be a good fix to your problem if you dont want it to be stiff and the end of the travel, if this isn't your race bike though I see no problem in having it ramp up at the end its easy to see if you are still getting full travel.
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
You can't really make a shock lack midstroke compression, especially when it uses a nearly identical compression damper to the DHX coil. I've explained this before but I guess I'm wasting my breath again - any midstroke dropoff will be due to the springrate. A positive/negative air spring is always going to have a curve, you can't really get it perfectly linear like a coil spring, and often the curve is something like regressive to progressive hence the falloff.

If you have a bike with a crappy suspension curve (especially regressive), air shocks are going to feel like **** period.

IMO it works pretty well in something like a sunday which has a curve that is progressive to linear or progressive to *slightly* regressive, hence at least somewhat counteracting any springrate falloff in the middle of the stroke.

Anyway, the best tip I can give is play with adjustments - there's so much you can do with that shock before you write it off. There are guys here running them pulling times as fast as anyone else so if you're using it as an excuse you're a wanker.

You can change the springrate curve by playing with oil volume in the air chamber, hot tip for that is - remove the air valve core (shock body) with small pliers or valve core remover, and with a small tube + syringe, add some amount of oil. Play with the oil volume until the shock feels more like you want it to. I'm running 14ml at the moment, probably a good starting point.

Messy post I know, I could post up something so much more thorough but I figure if I'm wasting my breath anyway I might as well save the rest for myself. :/
 

norbar

Turbo Monkey
Jun 7, 2007
9,554
339
Warsaw :/
Evolver isix -6 . Preferably the double barrel version.


Udi. Thx for the info. I'll see how much it is an issue in my dh-230 yet I don't think the susp there is crappy ;) I think it works better than maestro.
 

Rick205

Monkey
Jun 20, 2006
200
0
UDI - thankyou for basically calling me a wanker and saying your wasting your breath on me, very nice of you.:clapping: - I have never read this previous post where you describe spring rates etc......

I asked for HELP - i did not say i was blaming the shock for not riding well or anything, i just asked to see if anybody had any tips.

I gather from other posts you have experience with shock tuning internally etc - i dont, so sorry for my lack of knowlege!

Ok if im going to alter oil levels:

1- What grade/type of oil do i put in there? i have 2.5, 5, and 7wt lying around in the garage from fork rebuilds.
2- How do i measure how much oil is in there in the first place - and where would you start with adding oil, just one/two ml at a time - ride and retry?

So, i wouldnt mind your help as you seem to be the one person with experience - i dont know why you think your wasting your breath though - you dont know me so dont assume im not listening or that im an idiot!!

Rick
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
Rick - my rude words were not at you, just the multitude of generic replies to your thread that always greet any question of this variety. Interestingly enough, 90% of users posting these responses haven't spent more than 5 minutes on the shock, let alone taking the opportunity to tune it correctly to themselves and the bike they are riding.

Clearly you were just regurgitating something you had heard here in your question, through no fault of your own. So yeah - that wasn't directed at you! :)
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
I saw a bunch while I was watching the race at buller last weekend, but if you're after QLD names - the last bike I saw one on was one of the murrell kids V10's (not sure which). Clearly the worst bike to put it on ever, but he's faster than you, and faster than me - you're seriously delusional if you think gear has that much affect on times/speed - you should see some of the setups socket showed me last weekend. There's guys near the top of elite running "custom tuned" shocks that literally don't rebound. You push them up and they take 15 seconds to return again.

It's a big eye opener really - guys on here (me included!) are being overly pedantic over the most unimportant crap, and as fun as it is, the fast guys are out there ripping it on setups varying from decent to oh-my-god-are-you-serious and doing just fine.

But yeah - the point I was trying to make was, if you want to win on a DHX Air, you sure as hell can do it. It can be made to work pretty sweet with a bit of playing around (and an open mind), and provided it's working correctly and not busted - it's very likely NOT your limiting factor.
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
1- What grade/type of oil do i put in there? i have 2.5, 5, and 7wt lying around in the garage from fork rebuilds.
2- How do i measure how much oil is in there in the first place - and where would you start with adding oil, just one/two ml at a time - ride and retry?
Okay - the shock's air chamber runs a small amount of oil from factory to keep the seals lubed.

Firstly, depressurize the main air chamber of the shock (but leave the boost/piggy valve pressurized). Once you've removed the valve core from that valve (main air chamber), drain any remaining oil out - like I said there's a small amount. If you can, drain it into a medicine cup or something so you can see how much was in there in the first place.

Assuming about 5ml came out, I'd try the shock with 15-20ml in there. Let's say add 10ml on top of whatever came out to start off with, so if you drained 5ml, put 15ml in. As for oil weight, something thick is beneficial as apart from taking up volume, the other purpose is just lubing the seals. I use silkolene pro-RSF 10wt, from your oils just use the 7.

Do some runs, see how it rides etc. Try adding say 5ml at a time after that to see if it helps your issue at all, you might need to back off the bottom out adjuster as you do this to stop the shock ramping up too much. Remember if you change the bottom out adjuster that you also need to reset the boost valve pressure.

Feel free to play with boost valve pressure and propedal settings too, listing your current settings would probably be a good starting point - but after you've attacked the springrate as much as possible, the second point of tuning WILL be compression damping so some will indeed be beneficial.

My only other findings on the shock so far are:
a) You can bleed them incredibly easily, like a brake - which makes trying different oil weights in the damper very easy compared to conventional shocks. I'll post a how-to at some stage with pictures when I can get around to it.
b) The rebound on some of them plays up (doesn't sound like you have this problem though), some people incorrectly assume that it's to do with heat - heat has nothing to do with it (in fact I don't find heat has a noticeable effect on performance at all, at least in the 2.6:1 leverage frame mine's on), rather I believe it's something to do with a return valve/shim on the main piston - will check mine out when I open it up and post my findings too.
c) Unrelated - but make sure your shock is bled right, if it's overly noisy / making really loud sucking noises etc it might have a poor bleed (generally quieter is better) and a poor bleed WOULD indeed mean damping inconsistencies. From what I've seen, fox shocks are generally bled reasonably well though.

Well that's everything I know - hopefully you get it working to your liking, but yeah like I said keep an open mind and you'll probably wind up liking it.
 

Rick205

Monkey
Jun 20, 2006
200
0
Thanks for taking the time to make that detailed reply - sorry for coming back at you, looked like it was directed at me no the airshock hater groupies.

Im going to to shopping today and pickup some 10wt oil and have a go at this tmrw.

Did you ever try the grease in the main chamber thing? or will that just add additional stiction to the shock?

No, my rebound is fine and the range of adjustments work fully.

I believe my frame is a 3:1 ratio, its the lapierre dh230 - so is a quite high ratio when comparing it to the sunday.

Thanks again, ill post up how i get on.

RIck
 

DirtyMike

Turbo Fluffer
Aug 8, 2005
14,217
807
My own world inside my head
Udi, This is the first time I have seen that info posted here, good stuff. Myself and teh other guy I work with at the bike shop have been playing with oil levels in the air chamber for years. Its a wonderfull trick, and I am glad to hear I am not crazy for doing it, seeing how someone else belives in it as well, thank you. And very good description By the way!!!
 

slowracer

Chimp
May 14, 2006
18
0
Udi, I'm interested with the shock rebuild guide/instructions. I'm happy to do a dhx coil but havent done an air yet. Was gonna work on mine but waiting for a step by step first coz i cant figure out how to bleed it without special tools.

BTW i also done the oil in the main chamber tune on my dhx air and it works well, with much better midstroke damping. cant remember how much i put in coz wrote it down at the workshop.

Thanks in advance.
 

norbar

Turbo Monkey
Jun 7, 2007
9,554
339
Warsaw :/
Udi great info. I heard about it but seen no specific info. If I will feel the same issues on jumps as Rick (and probably will as it is the same bike and the lack of midstroke is noticible) definately gonna use it.
Probably you saved some money for some ppl ;)

But I still want a Bos shock :P
 

Rick205

Monkey
Jun 20, 2006
200
0
Right, got my bike out today, (been about 2 months since its last ride) - the shock sounds like crap, sucking squelching noises and inconsistant rebound - wonderfull! :busted:

Looks like i have more problems than tuning then, i expect this means i need a rebuild , or do i just need to get/ do myself a bleed to get rid of air that is mixing?
 

dhkid

Turbo Monkey
Mar 10, 2005
3,359
0
Malaysia
its weird, i have heard of so many dhx airs having air in the damping bit of it. anyways, i have tried one of my friends when it was in that state, hardly gives any comp damping, but still works alright in rebound. makes the shox feel crap, bottoms out in the parking lot with the right sag.

get it bled properly, it makes a world of difference.
 

Rick205

Monkey
Jun 20, 2006
200
0
UDI/ any others who have done this - is the re-bleed easy enough to achieve myself or should i just send it out to mojo or similar?

You said that bleeding this shock was as easy as a brake, if thats the case then i would rather have a go myself first.

Rick
 

OGRipper

Turbo Monkey
Feb 3, 2004
9,707
145
NORCAL is the hizzle
Udi is the man on this one.

How about if we petition Fox or Push or someone to make an AVA-style adjustable main air chamber for the DHX air? Seems that would help, because you could "tune" the rate with a combination of pressure and volume...? Similar effect as changing the oil level? Messing with the boost chamber volume and pressure is pretty much a band-aid.
 

VMARTINEZ

Monkey
May 23, 2005
285
7
Your Shock issue may just be an Out of Box Failure from Fox. They had lots or issues with there air shocks last year. VM
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
Udi is the man on this one.

How about if we petition Fox or Push or someone to make an AVA-style adjustable main air chamber for the DHX air? Seems that would help, because you could "tune" the rate with a combination of pressure and volume...? Similar effect as changing the oil level? Messing with the boost chamber volume and pressure is pretty much a band-aid.
Cheers, but I reckon while it's a good idea it'd just add weight. The cool thing about the DHX air is that it offers a significant enough weight saving to be worth switching over (unlike say the Roco Air WC which is 80-90g heavier and therefore not heaps lighter than a Ti sprung coil shock). Adding/removing oil from the air chamber isn't that hard anyway, and alternatively (as you probably already know) you can fit the RP3 canisters on there too. :)

Right, got my bike out today, (been about 2 months since its last ride) - the shock sounds like crap, sucking squelching noises and inconsistant rebound - wonderfull! :busted:

Looks like i have more problems than tuning then, i expect this means i need a rebuild , or do i just need to get/ do myself a bleed to get rid of air that is mixing?
It's hard to say - I didn't want to post up anything about rebleeding until I figured out the rebound thing, can I ask you to explain what your rebound is doing in a little more detail? Mine just seemed to work intermittently (when cranked up) - damping sometimes / not others.

I suspect a faulty return valve/shim/spring and plan on finding out + solving it if at all possible. I have to get a strap wrench to remove the air canister first though - does anyone know if there's another way to remove it that won't wreck anything?

Anyway if yours is within warranty I'd sent it away for a rebuild (or if mojo doesn't charge tonnes) and mention the rebound thing to them so they can be responsible if it doesn't work when you get it back. I'll write something up about bleeding within the next few weeks but yeah not until I get an opportunity to figure out the rebound thing. Obviously rebleeding won't fix whatever the damper is doing (just get rid of the air/squelching) so it's probably not your complete solution right now anyway.
 

Rick205

Monkey
Jun 20, 2006
200
0
Well, upon looking at it, rebound control is limited, its very fast up until the last few clicks that would be slowest - but it is very slow on full rebound. It can be inconsistant in that it will rebound slowly deep into the stroke then very quickly later on.

My shocks not under warranty now and a mojo service is £95 plus postage!.:shocked:

Do you not think re-bleeding could solve my problem, its only been ridden 10-12 times really. - If i do bleed it i have read somewhere that someone just opened the bleed port near the rebound adjuster and cycled the shock in a bath of 2.5wt oil - could this work?

Rick
 

Udi

RM Chief Ornithologist: “I Brake for Birds”
Mar 14, 2005
4,726
819
Sounds like your rebound isn't too messed up. You can try the cycling under oil if you want, it probably won't do a great job.

My method - long story (very) short involves:

- Open main bleed port on shaft (under a bath if you have one handy)
- Thread in boxxer rebound bolt (hollow, 8mm) 3/4 turn
- Attach full syringe + tubing to bolt head
- Open secondary bleed port, near rebound adjuster
- Blast oil through

There's a bit more to it but I'd rather explain it properly with some pics later. Opening the main bleed port involves removing the white nylon plug, which is a pain - just be careful. Once removed, it exposes a 4mm allen key slot.

Oh yeah, and use a highend oil - this time because it's in the damper you need the real deal. Something with a high viscosity index to ensure minimal viscosity change over a temperature range. I use + recommend Silkolene Pro RSF (5wt would be good), the other option is Redline (Medium/Red).
 

Rick205

Monkey
Jun 20, 2006
200
0
Ok, i got the nylon plug out.

I have removed the secondary port plug and oil 'fizzed' out into the container i have, it was full of air - i dont know if this is normal but i suspect not.

Just a few Q's before i continue tomorrow and have a go bleeding:

- Do i remove the black plastic cap/membrane under the main bleed bolt or is this depressed when i screw in the boxxer bolt?

- Is the process ended under a bath when you remove the boxxer bolt submerged as this may allow air into the system if not?

- Finally, i assume i do this with no air in the boost valve?

Thanks very much for your help UDI - very much appreciated and sorry for all the Q's.

RIck
 

dhkid

Turbo Monkey
Mar 10, 2005
3,359
0
Malaysia
udi, the air cannister can be undone by hand. and its meant to be tightened by hand too, not sure if you were aware of that. i have never had problems opening them up.
 

Rick205

Monkey
Jun 20, 2006
200
0
Yes, the air canister came apart by hand for me too so no need for the strap wrench there.

Rick
 

toodles

Turbo Monkey
Aug 24, 2004
2,655
817
Australia
I have removed the secondary port plug and oil 'fizzed' out into the container i have, it was full of air - i dont know if this is normal but i suspect not.
Stupid question - but you depressurised the boost chamber first right? if not, the piston depth will need to be reset.