AKgringo
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Twin tube, or Monotube?
I need to replace the shocks on my little SUV, and I am not clear about which design would serve my needs best. It is a light weight rig, and I abuse
it regularly in AK, Northern CA, and Baja.
The problem is that there is a hell of a lot of highway between those venues, so I don't want to just beef it up for the trail. My question is, does
one design have a significant advantage over the other in;
A, Off road
B, Highway
C, Durability
Thanks for any feedback, Gary
Edit; Oops, I meant to post this in the off road forum!
[Edited on 6-14-2018 by AKgringo]
If you are not living on the edge, you are taking up too much space!
"Could do better if he tried!" Report card comments from most of my grade school teachers. Sadly, still true!
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MMc
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I am a big fan of Bilstein, Fox, King. They all are good, my Kings were a bit stiffer but I could have had the valves changed out.
"Never teach a pig to sing it frustrates you and annoys the pig" - W.C.Fields
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Maderita
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A quality monotube is probably the way to go. Lots of people seem to like the Bilstein 5100 series. You said "little SUV" and "light weight rig." Many
light and/or modern SUVs and trucks have torsion bar suspensions with limited travel and short shocks. Your choices of shocks may be limited.
A lot of people seem to be critical of Rancho, but of the millions sold, there are bound to be complainers. I've had reasonable results on 1/2 ton to
1 ton trucks, Jeeps, Broncos, and 4x4 vans. The twin tube RS9000 is adjustable. For your purposes, that might work well. Turn a knob to stiffen or
soften their response.
My choice would be Bilstein 5100 if they make a shock to fit your SUV.
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David K
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I have Bilstein 5100s on all four corners of my 4-door Tacoma 4x4. They seem to be good and a big improvement over the TRD Bilstens that came on the
truck.
Old:
New:
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Cappy
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the 5100s are nice because they are completely protected. The exposed shaft on some of the other manufactures pits and you get seal failure.
Fox on the Van. Bilstiens on the truck
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basautter
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Bilstein 5100s have worked well for me for mostly pavement, some gravel and some off-road on my F250 diesel. One option is to get slightly oversized
tires, and air them down when you are off pavement. You may also consider tire deflators and a high flow air compressor to fill back up (discussed in
detail on another thread). This combo has worked well for me! 
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TMW
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I've used Rancho with OK results but I have used Bilstein for the last 8 years. The 5100 is hard to beat unless you go to a remote reservoir type
setup.
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AKgringo
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I appreciate the suggestions so far, but I am not finding any of the performance shock manufacturers looking to tap into the older Kia Sportage
market! Most of the "OEM replacement' offerings don't specify the internal design (twin or mono).
If you are not living on the edge, you are taking up too much space!
"Could do better if he tried!" Report card comments from most of my grade school teachers. Sadly, still true!
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Maderita
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AKGringo,
Your vehicle may have short (in length) shocks, making it difficult to find a quality aftermarket off road shock. That's a problem I encountered with
a Ford Explorer Sport Trac. Couldn't find 5100 shocks to fit. The best I could do is the standard yellow Bilstein (also monotube). Not complaining
though, the ride on and offroad is much improved.
An alternative to Bilstein is KYB Gas-A-Just. Also monotube. Reputed to be stiffer. A little less expensive. I prefer a stiff shock and have run KYBs
on a few vehicles. Even installed 4 KYBs on my off-road horse trailer with great results.
Edit: Looks like you might have struts in the front. The strut replacements from KYB may be twin tube. Your options for a serious upgrade are probably
quite limited. Maybe more options for rear shocks.
[Edited on 6-15-2018 by Maderita]
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AKgringo
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Thanks Maderita, I will probably go with another set of KYBs. I had them on my last Sportage, and the engine self destructed before the shocks
failed, so I never got an idea about their durability.
I checked the Blistein site, and the only one that fits my rig is a twin tube for a lower price than their monotube, but still more than the KYB. I
overload my little truck pretty often and drive some rough patches, and it sounds like a monotube may last longer.
If you are not living on the edge, you are taking up too much space!
"Could do better if he tried!" Report card comments from most of my grade school teachers. Sadly, still true!
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John Harper
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Quote: Originally posted by AKgringo  | | Thanks Maderita, I will probably go with another set of KYBs. I had them on my last Sportage, and the engine self destructed before the shocks
failed, so I never got an idea about their durability. |
I've used KYB Gas-a-Just for many years, on both my Ford Rangers. I've been happy with them, no failures, lots of rough dirt roads, no abnormal tire
wear. Just my experience.
John
[Edited on 6-15-2018 by John Harper]
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TMW
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I came across this and thought it may be of interest.
Mono-Tube vs Twin Rube Shocks
There are many rumors and discussions regarding which type of shock absorber is better, the Mono-tube or the Twin-tube? Mono-tube and twin-tube are
known as two different types of suspension systems that each work in very different ways.
Mono-Tube
In a mono-tube shock absorber, the shocks components are contained within one tube. A mono-tube system contains a shell case which works as a
cylinder. Within that cylinder you would find a piston valve, oil, and gas. The construction of a mono-tube does also include some differences
compared to the twin-tube design. A mono-tube design utilizes a free piston which separates the oil chamber from the gas chamber within the shell
case.
Twin-Tube
In a twin-tube shock absorber there are 2 cylinders: 1 cylinder is set inside the shell case, and the second cylinder contains the piston valve which
moves up and down within this second cylinder known as the “inner cylinder”. With a twin-tube design, there is no piston or barrier between the
oil chamber and gas chamber.
Pros and Cons of Mono-Tube Shock Absorbers
Pros of Mono-Tube
As temperature increases, oil is able to release heat with less effort.
Zero restrictions on installation angles.
Less prone to cavitation
Larger oil capacity and greater heat dissipation allows for a stable damping force that is continuous.
Air is not able to penetrate the oil or gas since they are completely separated.
100% efficiency through all temps.
The piston valve is bigger and wider in a mono-tube design which allows for a wider area of pressure. In turn this means the shock can create even a
subtle damping force precisely.
Cons of Mono-Tube
A stiffer ride is expected because an injection of high pressured gas is required in the structural design.
This high pressured gas can also lead to a higher amount of stress on seals which can cause more friction.
More expensive to manufacture
When there is external damage or force on the shell case, that directly affects the inner cylinder.
Since the oil and gas chambers are positioned next to each other, it is increasingly difficult to maintain sufficient stroke.
The inverted design has more friction caused from more moving parts.
Pros and Cons of Twin-Tube Shock Absorbers
twin-tube
Pros of Twin-Tube
Unlike the inverted design, friction can be stopped.
External damage to the shell case does not effect the shock absorber.
The twin-tube design provides a superior manufacturing process which keeps the cost of production low.
Gas pressure is kept low thanks to the base valve, this creates a more comfortable ride.
Low gas pressure reduces stress on seals and also keeps friction to a minimum.
Sufficient stroke is attained with far less effort. This is because each oil and gas chamber are separated.
Cons of Twin-Tube
The construction causes difficulties when installing.
Aeration is possible since the oil and gas chambers are not seperated.
Size of Piston is greatly decreased compared to the mono-tube design.
Oil capacity is reduced in comparison to the the mono-tube.
Low Pressure – Generally very Soft
Small Pistons, more prone to heat and limited on damping
CAVITATION- Fluid and gas mix, exponential performance loss up to 35%
1 Directional Mounting
All ISC Suspension systems use the mono-tube design for performance purposes along with the fact that the pros of the mono-tube design greatly
outweigh it’s cons.
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PaulW
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Tom, Thanks for posting.
The choice of shocks type based should be based on the use you expect. Well this is a Baja forum and as you all know we are have terrible washboard
roads as soon as we leave the pavement. That means that the choice would be based on acceptance of the more firm ride and choose the mono-tube over
the twin-tube.
Lots of people do not like the mono-tube solely based of the firm ride and choose the Twin-tube then find the shocks do not last. For sure most after
market mono-tube shocks will be noticeably stiffer than stock.
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DaliDali
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I had yellow Bilsteins on a 97 F-250 4x4 with those front leaf springs.
The ride was so harsh, I had to take them off before I lost every tooth in my mouth.
I replaced them with some Monroe Reflex light truck shocks....ahhh a 100 times better ride and saved what teeth I had left.
But I don't do off road other than that awful 22 miles of dirt/rock on MX 5
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AKgringo
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Thanks Tom, I found another comparison of the two designs that backs up the one you posted. It looks like monotube is the way to go for me.
If you are not living on the edge, you are taking up too much space!
"Could do better if he tried!" Report card comments from most of my grade school teachers. Sadly, still true!
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