Twin-tube versus monotube shock discussion

[suicidal2af]

What's better one or two? Two sounds safer...?

What's better? Monotube.

Monotube means there's a single oil chamber. Twintube has two oil chambers whiche allow oil to move between them during dampening. It's subject to cavitation. It also dissipates heat less readily, since it heat needs to pass through both tubes.

Monotubes can also have larger pistons which give more adjustability to valving and the piston holes, which means you can have a faster-reacting shock.

There are a few other advantages, such as the ability to have an inverted shock, but that's getting outside of our scope.

That said, a quality twin-tube, like a koni, can come close to the performance of a monotube, and usually will have a slightly better ride.

 

[jtmcinder]

What's better?Monotube means there's a single oil chamber. Twintube has two oil chambers which allow oil to move between them during dampening.

Are you suggesting that the oil in the "two chambers" of a twin-tube isn't really all one, continuous supply of oil?

Are you suggesting that the oil in a monotube doesn't move?

[The oil in a twin-tube is] subject to cavitation.

Are you suggesting that monotubes never suffer from cavitation?

It also dissipates heat less readily, since it heat needs to pass through both tubes.

Agreed.

Monotubes can also have larger pistons which give more adjustability to valving and the piston holes, which means you can have a faster-reacting shock.

Please explain why a monotube "reacts faster" than a twin-tube.

- Jtoby

 

[suicidal2af]

1)Are you suggesting that the oil in the "two chambers" of a twin-tube isn't really all one, continuous supply of oil?
2)Are you suggesting that the oil in a monotube doesn't move?
3)Are you suggesting that monotubes never suffer from cavitation?


Agreed.


4)Please explain why a monotube "reacts faster" than a twin-tube.

- Jtoby

1) It's one continuous supply of oil which is forced through (usually) a smaller orifice, which lends itself to more cavitation and aeration
2) In comparison, oil in a high pressure monotube will have VERY little movement. The motion of the oil in a monotube is through the piston holes and valves and nothing else.
3) Do they *never* suffer from cavitation? No. However, they have FAR less than almost any twin-tube. Look at bilstein monotubes: they exert ~25 bar on the oil column -- that in and of itself helps almost eliminate cavitation.

4) A few reasons, actually:
4a) Given an aggresively driven car on a road course, the heat dissipation qualities of a monotube will stave off fade.
4b) Given a set diameter, a monotube will have a larger piston area; this will give greater sensitivity to small movements.
4c) Monotubes tend to be lighter, reducing unsprung weight and increasing response to changing road conditions.

And the ability to mount them inverted will further reduce unsprung weight, but I guess I'm getting ahead of myself.

 

[jtmcinder]

1) It's one continuous supply of oil which is forced through (usually) a smaller orifice, which lends itself to more cavitation and aeration
2) In comparison, oil in a high pressure monotube will have VERY little movement. The motion of the oil in a monotube is through the piston holes and valves and nothing else.

The amount of "movement" (as you put it), depends on only two things: the diameter of the shock's shaft and amount of travel. Neither of these are intimately tied to whether the shock is a monotube or a twin-tube or whether the shock is low- or high-pressure, so your claim that movement depends on shock type is false.

3) Do they *never* suffer from cavitation? No. However, they have FAR less than almost any twin-tube. Look at bilstein monotubes: they exert ~25 bar on the oil column -- that in and of itself helps almost eliminate cavitation.

OK, so cavitation depends on pressure. But this only relates to the original question of monotube vs twin-tube if pressure is perfectly correlated with whether the shock has one or two tubes.

The rest of your post gives some good reasons why monotubes are more consistent and help in other ways, but not why they might "react faster." If we are really interested in the delay of damping forcing, I can see how shaft diameter might play a role, but this is not an auotmatic difference between monotubes and twin-tubes.

But it is nice to be having a discussion of this sort.

- Jtoby

 

[suicidal2af]

The amount of "movement" (as you put it), depends on only two things: the diameter of the shock's shaft and amount of travel. Neither of these are intimately tied to whether the shock is a monotube or a twin-tube or whether the shock is low- or high-pressure, so your claim that movement depends on shock type is false.

Not exactly correct. There are a few ways twin-tubes are made: Open gas, allowing the gas and oil to mix, with the gas in a 'bag', and with the gas trapped in 'foam'. Open gas will easily allow the oil and gas to mix, and we know what that leads to. Gas 'bags' alleviate this issue, but over time the material the bag is made of (usually plastic) breaks down, and you end up with the same problem. I don't know too much about the foam ones, however the design isn't often used, so I can only assume there's a legitimate reason for that.

The amount of pressure you can use in a twin-tube is also limited by design, and the gas will compress some as a result of the lower pressure, which means you now have three factors: Diameter of damper's shaft, amount of piston travel, and compression of the gas(and/or mixing of gas and oil). Monotubes lack this design flaw, instead having high pressure gas and a dividing piston. The gas still has a possibility of compressing, however when you're running 6 times as much pressure, it won't compress anywhere near what a low-pressure twintube will.

OK, so cavitation depends on pressure. But this only relates to the original question of monotube vs twin-tube if pressure is perfectly correlated with whether the shock has one or two tubes.

See above. Assuming an equal pressure and gas bag twintube vs monotube, there may not be any difference at first, but over time, once the bag breaks down, the twintube will lose its dampening abilities while the monotube still trucks on.

The rest of your post gives some good reasons why monotubes are more consistent and help in other ways, but not why they might "react faster." If we are really interested in the delay of damping forcing, I can see how shaft diameter might play a role, but this is not an auotmatic difference between monotubes and twin-tubes.

I should probably rephrase the whole 'react faster' thing, since you seem to be taking it in a different context than intended. When I say it reacts faster, what I mean is that it's more sensitive. Yeah, it's probably possible to take monotube x and create a twintube y that is just as sensitive.

But in the real world, we have packaging constraints. Given a set amount of space available for a damper to fill in any application, and a damper body that fills up the set amount of space, the monotube will always have a larger piston, which will displace more oil, which will make it more sensitive than a twintube with the same diameter body.

And then there's the fact that you can run it inverted, reducing unsprung weight, making the lighter part of the damper do the movement. That gives it a pretty good edge in sensitivity, too.

But it is nice to be having a discussion of this sort.

- Jtoby

Yeah, but the negative rep was a bit unwarranted.

 

[jtmcinder]

Not exactly correct. There are a few ways twin-tubes are made: Open gas, allowing the gas and oil to mix, with the gas in a 'bag', and with the gas trapped in 'foam'. Open gas will easily allow the oil and gas to mix, and we know what that leads to. Gas 'bags' alleviate this issue, but over time the material the bag is made of (usually plastic) breaks down, and you end up with the same problem. I don't know too much about the foam ones, however the design isn't often used, so I can only assume there's a legitimate reason for that.

What the heck does any of this have to do with the fact that the amount of oil movement depends on shaft diameter and amount of travel? Seriously. Are you channeling DG?

The amount of pressure you can use in a twin-tube is also limited by design, and the gas will compress some as a result of the lower pressure, which means you now have three factors: Diameter of damper's shaft, amount of piston travel, and compression of the gas(and/or mixing of gas and oil). Monotubes lack this design flaw, instead having high pressure gas and a dividing piston. The gas still has a possibility of compressing, however when you're running 6 times as much pressure, it won't compress anywhere near what a low-pressure twintube will.

Nope. The pressure is irrelevant because the oil is not compressible. As the shaft enters the shock-body, it displaces oil downward (assuming an upright shock) as a function of two and only two things: the diameter of the shaft and amount of travel. In other words, shaft volume entering the shock displaces oil volume downward. Whether the oil compresses a gas in the foot of the shock (monotube) or at the top of an outer tube (twin-tube) is irrelevant. The amount of oil that moves down is exactly equal to amount of shaft entering the shock because the oil is not compressible.

I should probably rephrase the whole 'react faster' thing, since you seem to be taking it in a different context than intended. When I say it reacts faster, what I mean is that it's more sensitive. Yeah, it's probably possible to take monotube x and create a twintube y that is just as sensitive.

Fine. But keep in mind that this is mostly due to the size of the channels in the piston head and the pressure, and has little directly to do with whether it is a mono- or twin-tube.

But in the real world, we have packaging constraints. Given a set amount of space available for a damper to fill in any application, and a damper body that fills up the set amount of space, the monotube will always have a larger piston, which will displace more oil, which will make it more sensitive than a twintube with the same diameter body.

No. No. No. The piston doesn't displace the oil. It's the shock's shaft entering the shock's body that displaces oil. This is very basic and would appear to be your problem. Oil moves through the piston's head and/or the head moves through the oil, but the displacing is done by the shaft. The piston head does not change size as it moves.

Yeah, but the negative rep was a bit unwarranted.

Are you sure it came from me? I usually wait to see if the person self-corrects before acting.

- Jtoby

 

[suicidal2af]

What the heck does any of this have to do with the fact that the amount of oil movement depends on shaft diameter and amount of travel? Seriously. Are you channeling DG?

Are you saying that the piston does not displace oil? If that were the case, there would be no point to having the piston -- it displacing oil is HOW a damper works. It displaces oil, forcing the valve on the piston open, moving oil from bottom chamber to top chamber and vice versa.

Edit: What I meant to say here is that without the piston to displace oil, you would just shoot the shaft straight through the bottom, and wouldn't do much good. The piston is what makes the whole thing work.

Nope. The pressure is irrelevant because the oil is not compressible. As the shaft enters the shock-body, it displaces oil downward (assuming an upright shock) as a function of two and only two things: the diameter of the shaft and amount of travel. In other words, shaft volume entering the shock displaces oil volume downward. Whether the oil compresses a gas in the foot of the shock (monotube) or at the top of an outer tube (twin-tube) is irrelevant. The amount of oil that moves down is exactly equal to amount of shaft entering the shock because the oil is not compressible.

And the piston displaces oil upward. It goes down, oil goes through it. Sounds like displacement to me.

And I realize the oil is not compressible, that's where the gas pressure comes into play. A low pressure twintube is going to compress its gas more than a high pressure monotube, effectively increasing the volume of the shock. Ergo, reducing the dampening ability.

The shaft reducing the volume is part of the reason a damper works. If it didn't, it wouldn't take an exponential amount of force to fully compress it. It would actually make shock dynos a pretty boring thing to look at, actually.

Fine. But keep in mind that this is mostly due to the size of the channels in the piston head and the pressure, and has little directly to do with whether it is a mono- or twin-tube.

Has quite a bit to do with it's mono or twin-tube. By design, given equal size dampers, a monotube will always have a larger piston head.

No. No. No. The piston doesn't displace the oil. It's the shock's shaft entering the shock's body that displaces oil. This is very basic and would appear to be your problem. Oil moves through the piston's head and/or the head moves through the oil, but the displacing is done by the shaft. The piston head does not change size as it moves.

dis·place (ds-pls)
tr.v. dis·placed, dis·plac·ing, dis·plac·es

1. To move or shift from the usual place or position, especially to force to leave a homeland: millions of refugees who were displaced by the war.
2. To take the place of; supplant.

It does displace oil. If it didn't, it wouldn't do anything at all.

Are you sure it came from me? I usually wait to see if the person self-corrects before acting.

- Jtoby

Well, only wisemen and mods can give negative rep, and you and wret are pretty much the only 2 that frequent this side of the board, and I know which one he left ;P

 

[suicidal2af]

To better explain the sensitivity issue, let's draw an analogy.

Let's say you are jumping on an air mattress. Inflate it half way and take a hop on it. You'll push into it, increasing the pressure in tha mattress, before it stops moving and supports your weight. Now overinflate it so it's pretty much rock-hard. As soon as you hit it, you'll stop.

Essentially, because of the extra pressure, there's less of a "deadzone" than in a low pressure twin-tube. The oil doesn't compress, but with the lower pressure gas bag, the bag compresses, requiring more oil displacement before it really becomes effective. This isn't as much of an issue with a monotube, because the gas pressure is much higher. Even if it does compress some, it won't be anywhere near the extent that a low pressure bag will.

This is not to say that the gas in a monotube doesn't compress at all -- it certainly does, and the dividing piston is free-floating to accomodate for this. It just serves more of a purpose.

 

[wret]

Good discussion guys, and as you can see I've moved it to a separate thread. Please don't forget to help the original poster out in the original thread.

 

[jtmcinder]

I can't respond much right now, but will say this: you seem to be using the word "displace" incorrectly, such that maybe one thing is causing much of the problem. Piston heads do not displace oil other than always using up a constant amount of space in the main tube. What actually displaces oil is the shaft of the shock entering the body.

This concept is missed by a large number of people. It is why you have to have the gas or sponge or foam or whatever. There needs to be something compressible in the shock to allow for the volume of the shaft that enters the shock-body during bounce. And it is this added volume that causes the oil to move.

If it weren't for the volume of shaft entering the shock during bounce, then the simple model of how a shock works that about 95% of all people seem to have in their heads would be correct. Under this simple but erroneous model, the oil doesn't really move much. Instead, the piston-head moves through the oil.

But the shock's shoft does take up space inside the shock. And the more of the shaft inside the shock, the more space is being used by the shaft. This causes the oil to shift downwards during bounce.

Going one step further -- and ignoring the snide comment by my wife that I don't seem to be doing what I'm supposed to -- the downward movement of oil during bounce plays a huge role in the design of the better OTS shocks, such as Koni Sports. These shocks do not have all the critical valving in the piston-head. Instead, the control of compression damping (during bounce) is mostly performed by a valve in the bottom of the shock, controlling the flow of oil from the main (inner) tube to the reservoir (outer) tube. Koni calls this thing a "foot-valve" since it's in the foot of the shock. Meanwhile, the control of rebound damping is in the piston-head.

By separating the valves that deal with compression and rebound, Koni can do lots of valving in a very thin shock, since they have twice the area to work with: i.e., the foot plus the piston-head. That's why Koni Sports can be so skinny and still be so darned good. Plus, by seperating the valving, the adjuster on a Koni (which goes down through the shaft to the head) can adjust rebound only, which is much better than a single adjuster that does both rebound and compression.

In contrast, your typical Asian-style adjustable twin-tube (e.g., Illuminas) only have valving in the piston-head, so adjustments affect both rebound and compression.

Anyway, please sit down and digest the idea that the shaft entering the body is what displaces oil. We really won't get anywhere until you grok this.

- Jtoby

 

[suicidal2af]

I can't respond much right now, but will say this: you seem to be using the word "displace" incorrectly, such that maybe one thing is causing much of the problem. Piston heads do not displace oil other than always using up a constant amount of space in the main tube. What actually displaces oil is the shaft of the shock entering the body.

This concept is missed by a large number of people. It is why you have to have the gas or sponge or foam or whatever. There needs to be something compressible in the shock to allow for the volume of the shaft that enters the shock-body during bounce. And it is this added volume that causes the oil to move.

If it weren't for the volume of shaft entering the shock during bounce, then the simple model of how a shock works that about 95% of all people seem to have in their heads would be correct. Under this simple but erroneous model, the oil doesn't really move much. Instead, the piston-head moves through the oil.

But the shock's shoft does take up space inside the shock. And the more of the shaft inside the shock, the more space is being used by the shaft. This causes the oil to shift downwards during bounce.

Going one step further -- and ignoring the snide comment by my wife that I don't seem to be doing what I'm supposed to -- the downward movement of oil during bounce plays a huge role in the design of the better OTS shocks, such as Koni Sports. These shocks do not have all the critical valving in the piston-head. Instead, the control of compression damping (during bounce) is mostly performed by a valve in the bottom of the shock, controlling the flow of oil from the main (inner) tube to the reservoir (outer) tube. Koni calls this thing a "foot-valve" since it's in the foot of the shock. Meanwhile, the control of rebound damping is in the piston-head.

By separating the valves that deal with compression and rebound, Koni can do lots of valving in a very thin shock, since they have twice the area to work with: i.e., the foot plus the piston-head. That's why Koni Sports can be so skinny and still be so darned good. Plus, by seperating the valving, the adjuster on a Koni (which goes down through the shaft to the head) can adjust rebound only, which is much better than a single adjuster that does both rebound and compression.

In contrast, your typical Asian-style adjustable twin-tube (e.g., Illuminas) only have valving in the piston-head, so adjustments affect both rebound and compression.

Anyway, please sit down and digest the idea that the shaft entering the body is what displaces oil. We really won't get anywhere until you grok this.

- Jtoby

Not to argue semantics, but the piston DOES displace oil. If it didn't, why would it need holes or valves? It wouldn't. Try this: if you have a pool, take a garbage can lid, punch some holes in it, and push it down into the pool as hard as you can. You'll see all kinds of fancy cavitation and aeration as you do it. Now, once it's submerged, do the same thing. And notice the same effect.

Again, read the definition of displace. The piston is definitely displacing oil, unless it manages molecularly merge with the oil -- however, pretty sure that doesn't happen. Just because the piston isn't reducing the overall volume of the damper does NOT mean it isn't displacing anything.

Here's the thing -- almost *all* twin-tubes have valves at the bottom. The technical term for it is a base-valve. Everything from Koni Sports to your $29.99 Monroe Sensatracs have them. It's a basic part of the twin-tube design.

So why does a Koni outperform, say, an AGX or an Illumina? Better base-valve design. If it weren't for the base valve, the gas bag would just compress and make the damper utterly useless. Much like soft rubber bushings do in a suspension, actually.

By design, that is not an issue with a monotube. You don't just have oil being forced down into a low pressure bag, squeezing it down. The high pressure gas does the work of the base valve AND the gas bag.

The fact of the matter is, there are only 2 areas a good twin-tube will be better than a good monotube: Durability, since a dent in the side of a twin-tube won't affect operation, whereas it kills a monotube, and comfort, since the low-pressure bag will give the same effect as soft rubber bushings and make for a more sloshy, comfortable ride.

 

[jtmcinder]

You don't seem to get this.

Of course, the piston-head takes the place of some oil, but that's not important because it is constant. What is important is how the shock's shaft displaces a variable amount of oil. When the shock is fully extended, almost no space inside the shock's body is taken up by the shaft. When the shock is fully compressed, quite a bit of space is used by the shaft.

Your garbage-can-lid-in-a-swimming-pool analogy misses this critical point. When you first put the lid in the pool, the water level in the pool rises. This can be thought of as the piston-head displacing some oil, but that's not really important because you are never going to take the lid out of the water, which is why I called this a conatant. Here's the important part: when you push the lid down lower in the water, putting more of your arm in the pool, the water level again rises. This is the shaft displacing fluid.

If you -- or anyone lurking -- has the idea that the oil just "sits there" in the tube and piston's head moves up and down through it, then you have to let go. I know that this fits the idea of a piston-head with valves, but it is very misleading. It is wrong because it only covers about half of the story with regard to damping and it's a part of the story that has almost nothing to do with the mono- vs twin-tube issue.

Again, the whole reason why there has to be some gas (or some other compressible material) in the shock is that the oil which is displaced by the shaft during bounce must have somewhere to go. Monotubes put this "storage space" at the bottom of the shock (or off in a remote reservoir); twin-tubes put the storage space at the top of the outer tube.

- Jtoby

 

[jtmcinder]

I have just enough time to deal with this one. I'll try to get to the rest later today.

By design, that is not an issue with a monotube. You don't just have oil being forced down into a low pressure bag, squeezing it down. The high pressure gas does the work of the base valve AND the gas bag.

A compressed bag of gas cannot take the place of a small-diameter or valved channel. It places no limits on how quickly it can be compressed or allowed to expand. It is only there to (a) provide a place for displaced oil to go during bounce and (b) maintain pressure inside the tube to reduce cavitation. It is not part of the damping system.

This is one of the advantages of twin-tubes: they can have foot-valves. The only ways to get the equivalent of a foot-valve in a monotube is to add on remote reservoirs (which is often done) or to extent the shock body to make room for a foot-valve below the lowest point of the piston-head and above the gas chamber (which is theoretically possible, but I've never seen it done).

- Jtoby

 

[suicidal2af]

You don't seem to get this.

Of course, the piston-head takes the place of some oil, but that's not important because it is constant. What is important is how the shock's shaft displaces a variable amount of oil. When the shock is fully extended, almost no space inside the shock's body is taken up by the shaft. When the shock is fully compressed, quite a bit of space is used by the shaft.

I'm not arguing that the shaft doesn't displace oil; but you seem to think that the size of the working piston makes no difference in the dampening ability of the damper, which is absolutely false. I'm not saying it's the whole story -- but it's a crucial part of the story.

[quoteYour garbage-can-lid-in-a-swimming-pool analogy misses this critical point. When you first put the lid in the pool, the water level in the pool rises. This can be thought of as the piston-head displacing some oil, but that's not really important because you are never going to take the lid out of the water, which is why I called this a conatant. Here's the important part: when you push the lid down lower in the water, putting more of your arm in the pool, the water level again rises. This is the shaft displacing fluid.[/quote]

Even if you are fully submerged, the lid will still displace water and resist movement. That's the whole point here -- more surface area on the piston head *will* make the damper resist up or down motion than one with lesser area.

If you -- or anyone lurking -- has the idea that the oil just "sits there" in the tube and piston's head moves up and down through it, then you have to let go. I know that this fits the idea of a piston-head with valves, but it is very misleading. It is wrong because it only covers about half of the story with regard to damping and it's a part of the story that has almost nothing to do with the mono- vs twin-tube issue.

I never said the oil just "sits there".

Again, the whole reason why there has to be some gas (or some other compressible material) in the shock is that the oil which is displaced by the shaft during bounce must have somewhere to go. Monotubes put this "storage space" at the bottom of the shock (or off in a remote reservoir); twin-tubes put the storage space at the top of the outer tube.

- Jtoby

Here's the issue, though: The twin-tube has much lower pressure gas. When the piston starts to come down(along with the shaft), it's going to almost immediately start compressing the bag. This effectively gives you dead time where the only resistance to the shock compressing or expanding is the surface area of the piston. A high pressure monotube doesn't HAVE this issue because of the higher pressure gas involved.

Even with a twin-tube with a well designed base valve, like a Koni, once you near full compression and the valve is open, you'll compress the bag of gas and have the same amount of the shock displaced, and you'll get some shock fade.

Which is one of the reasons that pretty much every motorsport you can name uses monotube as opposed to twin-tube.

 

[jtmcinder]

I took another look at this thread and will try one last approach.

Think about the two, basic, inexpensive shock designs: twin-tube and simple monotube (i.e., monotube without a remote reservoir). Now ask yourself which of these two is more similar to fancy, racing monotubes with remotes and three separate adjusters.

Please focus on the core issues when doing this. Ignore anything that is merely usually true of one type of design. Think only about the things that must be true.

- Jtoby

 

[jtmcinder]

Here's a hint to the answer.

The reason why shocks need to have a compressible something (e.g., a gas) is because the shock's shaft displaces oil during bounce.

This compressible something is a problem, because it allows the oil to cavitate behind the piston-head during bounce.

One way to reduce cavitation is to increase the base pressure in the compressible something, but this causes the shock to be a spring as well as a damper.

Another way to reduce cavitation is to move the main valve that controls damping during bounce to being between the piston-head and the compressible something (instead of in the piston-head, itself). This allows you to run a lower base pressure.

Now return to the question posed in the previous post. Ask yourself which approach a plain monotube takes and ask yourself which approach a twin-tube takes and then ask yourself which approach a fancy, racing, monotube with a remote reservoir takes.

- Jtoby

 

[wret]

I'm trying to come up with some drawings for the abstract-thinking challenged such as myself. Do these work?


Monotube Shock Absorbers

You must be logged in to view this image or video.

ABOVE: Cutaway drawings of 4 common monotube designs.
E=emulsion type where oil and nitrogen gas are mixed together.
D=divider chamber type.
P=piggyback type, where the divider chamber is piggybacked onto the main shock body
H=external reservoir type. The nitrogen reservoir is connected to the main shock body via a stainless braided line.

from www.ducatigarage.netfirms.com

You must be logged in to view this image or video.

from howstuffworks.com

 

[jtmcinder]

With regard to the monotubes, you can omit E from consideration. D is a basic monotube. P and H are monotubes with remotes.

As to that picture from "How Stuff Might Work," it has a huge error with regard to how twin-tubes work. The picture shows the base-valve just sitting off on the end doing nothing. In reality, oil moving from the main chamber under the piston-head to the outer chamber must pass through the valve. I will attach a cut-away of a Koni Sport.

- Jtoby

 

[underradar92]

The blue area is the compressed gas? This design seems to limit potential poston diameter, but trades that for seperating the two damping functions, making them more controllable, and (therefore?) sepreately adjustable. Or am I missing something?

 

[suicidal2af]

The blue area is the compressed gas? This design seems to limit potential poston diameter, but trades that for seperating the two damping functions, making them more controllable, and (therefore?) sepreately adjustable. Or am I missing something?

Actually, you hit the nail on the head. It's easier and cheaper to make a twin-tube adjustable, but with a constant body diameter it will have a smaller piston.

I never meant to argue that any monotube is better than a twintube, it was simply that a cheap monotube will always be better than a cheap twintube, and a high-end mono will be better than a high-end twin in almost any circumstance.

 

[jtmcinder]

When a cheap monotube (by which I assume you mean a monotube with no remote) gets hit hard and fast, what happens inside it?

When a cheap twin-tube (by which I assume you mean either a non-adjustable or one with a single bleeder adjustment) gets hit hard and fast, what happens inside it?

- Jtoby

 

[wongster]

When a cheap monotube (by which I assume you mean a monotube with no remote) gets hit hard and fast, what happens inside it?

When a cheap twin-tube (by which I assume you mean either a non-adjustable or one with a single bleeder adjustment) gets hit hard and fast, what happens inside it?

- Jtoby

thanks guys!!.. man that was a lot of reading, but now esp the diagrams.. kinda helped me understand how shocks work..

 

[jtmcinder]

When a cheap monotube gets hit hard and fast, the gas compresses and vacuum "cavities" appear behind the piston head. Under these conditions, the shock ceases to be a damper; it's just another spring.

When a twin-tube gets hit hard and fast, the foot-valve prevents the oil under the piston-head from moving down with the piston.

That's why your basic twin-tube is better than a cheap monotube.

Yes, fancy monotubes with remotes are better than just about any twin-tube, but your basic monotube is the worst of the lot.

That's why there is no simple answer to the question that started this thread.

- Jtoby

 

[underradar92]

I'm guessing those vortexes can/do sometimes draw some of the gas into the oil? Or does the cavitation create a foam of some sort. Or have I missed a valuable piece of the puzzle?

 

[jtmcinder]

Neither. The cavities that form behind the piston during compression are vacuum pockets. This is what happens when a plain monotube is hit hard and fast.

Then look again at the pictures I posted of Koni Sports. Note how everything above the foot-valve is under pressure during bump (i.e., it's all orange). The piston-head doesn't do any of the damping during compression on these shocks (which is why the adjuster only affects rebound). Therefore, there is almost no risk of cavitation. That is why they don't need high pressures. And that is why they don't act as springs.

No plain monotube can come anywhere near the level of performance of a Koni Sport.

- Jtoby