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Discussion Starter · #1 ·
I've recently heard that the DHX air is not a very sophisticated shock. I've heard that it has virtually no compression damping and is basically just an undamped air spring on compression.

I haven't had this verified yet, but it would tend to explain the wallowing and lack of mid-range support that users have been posting.

Apparently, the RP3 is a more sophisticated shock with real compression damping. I wonder if this is why Push will work on RP3s but not DHX Air shocks. You can't tune compression damping if none exists.

Apparently, the DHX Air is not a technological advancement ..... It's a marketing breakthrough!

Discuss
 

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Time is not a road.
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Doesn't it have Pro Predal as a compression damper? Perhaps is the lack of smooth rebound that the DHX-Air suffers from? Not the biggest suspension guru...
 

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Discussion Starter · #3 ·
chad1433 said:
Doesn't it have Pro Predal as a compression damper? Perhaps is the lack of smooth rebound that the DHX-Air suffers from? Not the biggest suspension guru...
I believe that it does have some form of propedal, but that is not the same as compression damping.
 

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Groveland Trail Heads
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Are you working

Blue Shorts said:
I believe that it does have some form of propedal, but that is not the same as compression damping.
today? You sure seem to have a lot of free time... hey maybe we should just call it a day and go ride! Ha, ha..... Are you talking smack about the DHX air? I could comment if I owned one but my RP3 is working just fine.
 

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Outcast
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Blue Shorts said:
I've recently heard that the DHX air is not a very sophisticated shock. I've heard that it has virtually no compression damping and is basically just an undamped air spring on compression.

I haven't had this verified yet...
So you are running away with unverified heresay and second hand info and starting a thread just to talk smack? Man, you must be bored.
It has a lack of mid range support. Many riders actually LIKE that, you may be suprised to know. The lack of typical mid range support does not equate to unsophistication in the product.
Why don't you ride one for a while, and then come back here and provide some feedback based on first hand experience, rather than unsubstantiated heresay?
 

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No, that's not phonetic
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I think the PP mechanism in the RP3 has changed quite a bit recently too, so making comparisons is a bit difficult.

If tuning options = sophistication, then the DHX A is more "sophisticated" than the RP3. Does it work better? I find them to be quite similar in use in the sense that you can set the DHX A up to feel a lot like the RP3. If you don't like the RP3, then you may not like a DHX A. I like 'em both.
 

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Bodhisattva
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As memory serves me,
high speed compression damping on both coil & air DHX are done through the boost valve. The DHX air incorporates a non-piston type of rebound mechanism which is a departure from previous Fox shocks.
 

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Discussion Starter · #9 ·
The tuning options are nice, no doubt, but when I referred to sophistication, I meant regarding the compression damping. Sure, the DHX Air has a BO adjustment, which is nice. It has Propedal level settings, which is also nice. What it's missing, is a compression damping circuit in the active range like the DHX Coil has (not the low speed pp damping).

Most of the DHX A complaints that I've heard about relate to 2 items. One is the large pressures required by the shock. The other is the lack of mid-range support, or wallowing, which is tied directly to the lack of a compression damping circuit.

Many people thought that the DHX A was the same as the DHX C, except it used an air spring instead of a coil spring. They're similar, but the lack of a compression damping circuit makes them behave very differently.

I'm not trying to bad-mouth the DHX A. I was just "shocked" :D to find out that the compression circuit is basically an empty can of air.
 

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carpe mañana
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Correct me if I'm wrong, but seeing the DHX air apart, and seeing its innards, there's clearly a piston with shims on both sides, meaning the compression and rebound are shimmed, leaving bleeds for slow speed and opening up at high speed. Furthermore, the boost valve is a oil metering valve which is acted upon by the force of oil flowing through and the air pressure on the other side of it. It is actually a position sensitive damping as the deeper in the stroke the shock is, the more air force acts upon the metering valve, resisting futher progression with more force than in the initial portion of the stroke. Pro pedal has very little to do with compression damping, other than in the initial portion of the stroke as the force of the spring that propedal is gets quickly overcome by the force of air in the boost valve. The lack of mid stroke support is simply the nature of the air spring. There's a large "flat" section of the spring rate curve in that portion of the stroke, so there's little spring force to support further progression of the shock. Damping only controlls the speed of the shaft movement, spring is what stores the energy of the impact and releases it on rebound.

_MK
 

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Discussion Starter · #11 ·
I'm not trying to talk smack. I got this information from someone that is usually highly reliable. He kknows a lot about shocks, particularly Fox shocks.

I posted this information to get people to discuss it. If I'm wrong....... fine. At least there will be discussion about the subject.
 

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Discussion Starter · #12 ·
I was led to believe that the piston is only in the circuit during rebound. I thought that the lack of a compression circuit was the primary reason that Push wouldn't work on DHX A shocks.

Hopefully Darren will sign in and clear things up here.
 

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PP is a function of the compression damper

I suppose that by using the PP adjust AND the compression you could deaden the compression...
 

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"El Whatever"
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Blue... _MK is in the industry too (at least part time, the last time I knew).

He said he teared one open and actually saw its innards. All he describes later make perfect sense too.

Now on the DHX's behaviour... the damping curve you get is partly due to the inherent charateristics of air springs. The rest is a "trend" of the industry of providing an initial high compression damping and then decrease it during mid-stroke and then ramp up by the end of travel.

Different mechanisms but the result is kinda the same. With SPV you have high initial resistance to slow/little obstacles, then the valving opens wide and then the increased hydro pressure on the SPV valve closes it preventing bottom out.

Fox does it in a similar way but thru different means.

What you can accuse Fox for is for providing too little mid-stroke damping. Which I would like in a shock and some people like too. Depending on your bike linkage and leverage, it might be the right shock or a perfect lemon.

As for the high pressures... I dunno. Maybe to overcome the stiction of the increased area of the seals you need a higher negative pressure which in turn increase the main spring pressure of the shock thanks to Fox negative/positive spring design???

Maybe someone can explain it. But I find weird that a platform shock with increased volume chambers would behave just like that. Both parameters should make the pressure to drop. But I'm no expert by any stretch of imagination.
 

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Bodhisattva
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I just clarified the innards

If you were to take apart a DHX air you would indeed find shims on both the rebound & compression part of the piston.

But while the compression shims are there, they don't function on the DHX-air like they do with other Fox shocks and the compression damping really takes place at the PP & BV.
 

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"El Whatever"
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The Squeaky Wheel said:
I just clarified the innards

If you were to take apart a DHX air you would indeed find shims on both the rebound & compression part of the piston.

But while the compression shims are there, they don't function on the DHX-air like they do with other Fox shocks and the compression damping really takes place at the PP & BV.
Shims are what are called "valve quality" surfaces and are rather expensive. Being them steel, a couple grams they do weigh... you don't put them in a shock if you're not going to use them.

So, what is the use of the shims of the compression side of the piston? Do they do the high-speed damping job? If so, maybe you'll not notice much its work.

You hang around a lot with Darren and gotta know what you're talking about... I'm asking for curiosity sake.
 

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"El Whatever"
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The Squeaky Wheel said:
in the DHX air they serve as a non-return circuit.

And that has completely exhausted my knowledge base at this point :)
Doesn't make much sense... But if Darren says so... ;)
 

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No, that's not phonetic
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I think MK_ spelled it out well. The lack of mid-range support is a function of the shape of the spring curve. The air shock is gently sloping for a while and then ramps up, basically AFTER the mid point is passed. The coil is linear and so does not have this sort of "saddle" in the middle. They would not have put a boost valve and bottom out adjuster on the Air if they did not want the compression damping to be position sensitive. If you raise the BV pressure and also make the BV chamber smaller via the BO volume adjust, you increase the compression damping and make it close down faster as you go through travel. The mechanism may be a bit diff than the coil, but the results appear to be about the same. The RP3 lacks all of these whistles and bells afaik.
 

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Discussion Starter · #20 ·
Thanks for the clarification. I wasn't trying to bad-mouth the DHX A or Fox. I guess the Marketing breakthrough thing didn't go over well. It's kind of an inside joke.

At least we have a good conversation going and I'm learnig more about the shock than I knew previously.
 
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