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So you want to know about suspensions?

suspension tracks spring torsion suspensions volute bogie running gear

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TheManWithNoName #1 Posted Nov 04 2012 - 11:59


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Disclaimer: I am new to this forum, if th isis the wrong format, section or otherwise has any issues, I apologize in advance.
So you want to know about suspensions?

The area of suspension design is a surprisingly complicated one, and one which has shaped tracked vehicle design--both of tanks and support vehicles--since their conception back before world war 1.  The idea of a suspension system to dampen impacts on the chassis and to decrease the force on the tracks from terrain has been well known, with many approaches leading to many effects.  Let's first look at the reason why a tank needs a suspension.

Tracked vehicles need suspensions for three primary reasons: comfort, traction, and track life.
The first of which is obviously the comfort of the crew.  Going over shell craters, dips, rocks, bumps, etc, at high speed is a nerve-racking experience--bounced around in a steel can, surrounded by ammunition, with little visibility.  This oscillation and bucking can damage tank components--much like sliding down too sharp a ravine in your T-50--and the crew can even pitch into the objects within the tank, literally being thrown about and even injured.
The second of which is traction.  When a tank goes over a rut, if the tracks are perfectly flat--like that of most bulldozers--only a portion of the track will be in contact with the ground, and hence ground pressure goes up.  Conversely, on a hill, the center of the tracks is under more pressure, and will dig in more readily.  The second, and more critical, issue with this is that steering is affected.  Tanks don't steer like cars, you don't simply turn a wheel and go X degrees.  Most tanks of the WW1 through vietnam era used levers, which slowed one track; even modern tanks, by turning their tiller bar or wheels, apply X amount extra force to one side and subtract to the other.  This means that steering is affected by traction.  Ideally, for smooth turning, a tank should have fairly balanced ground pressure along its track length, gradually increasing as it reaches the center; the ends of the tracks at the front and back of the tank have to slide sideways to turn, with more sliding the further up the length of the tank you go.  So having fairly uniform traction means the driver's control inputs are relatively steady, whereas without suspension and with unequal ground pressure, a turn that normally would have been a gentle slew to one side could spin the tank suddenly around, or not move it at all.
The third reason for a tank's suspension is track life.  Tank tracks are not like car tires, they wear out fast and often need replaced.  They are also very expensive.  Some tanks in WW2 have been quoted as having tracks that only lasted as little as 250km.  While the lifespan of hte tracks varied according to design and the weight of the vehicle, having a suspension that attempted to keep equal pressure from each bogie wheel was a necessity for any track life early in the war.  This became less relevant later, as longer-travel designs such as that of the Panther and Pershing were introduced.

Tracked vehicle suspension is balance of factors: size, travel, longevity, and logistics.
First, the size of the suspension component is a big factor--a large, bulky system will add weight and has to be armored.  More weight means a slower tank, exponentially so when you consider that usually these systems have to be armored if they are not particularly durable.
The travel of the suspension is incredibly important, adding to all three of the above-mentioned needs.  More travel lets the tank cross more rough obstacles and gives it more flex.  It also can usually add to the smoothness, and hence its top speed--I recall a certain British tank with a very high top speed from its engine, but which could never acheive it in practice due to shaking itself to bits over rough ground.  It means that it also produces less sharp impacts on the tracks themselves, meaning they last longer (compare pushing on something with hammer, versus hitting it).
Longevity, or the lifespan of a suspension, was a relatively minor issue in regular use.  Most of the suspension designs even in world war 1 were fairly effective in terms of lasting.  The issue was combat damage.  Two major approaches to suspension design emerged in the world during WW2, that of putting suspension under armor, and that of making the suspension easily removed and replaced.  Both are, to an extent, used today, but under-armor suspension is generally the new norm.
Logistics, or the cost, was a relatively minor issue but one which showed up in a few instances.  The infamous overlapping and interleaved roadwheels of the German big cats, for instance--not a design flaw, but a response to the lack of rubber available.  Since rubber was necessary to reduce track friction with the wheels, the Germans instead used more roadwheels to reduce the wear of the roadwheels on the track, eventually using all-steel wheels with small internal shock absorbers.  The Russian T-34, produced in great numbers, had a very poor and outdated track design which was prone to breaking, but was simple to produce and the only real option available to the soviet union.  So we see a few unique examples of this.

So, enough about the needs and purpose.  I want to see the facts!  Let's see some suspensions!

The first is obviously that used in WW1 on the British tanks so well known--no suspension.  This is fairly self-explanatory--roadwheels bolted directly to the hull.  Interesting tidbit--if you look up bovington tank museums youtube, on the little willie they mention the tracks had guide rails but also flanges to prevent track slipping.  Later variations had the tracks on big modules connected to the hull with a girder, like the Whippet.  I won't go into the reasons why this was a bad system.

Coil Bogie (non-horstmann)
From the period of WW1 until WW2, this was a form of suspension often used, with a single or multiple coil springs carrying a bogie.  This was a big improvement, but still only capable of very minimal travel.  Later versions would be articulated, to allow it to pivot and help with interconnection and give travel.  The system was limited by the size of the compressed spring, meaning that travel was fairly minimal.  This suspension was fairly much phased out by the late interwar years, seeing its first use on some French WW1 tanks and the A7V.
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Leaf-Sprung Bogie
While the first implementation of this I don't recall offhand, it was widely copied after being used, combined with high-strength steel tracks with very small links to reduce rotational friction, on the Vickers six-ton.  In a nutshell, this system is a pair of wheels, carried on leaf sprigs or leaf sprung arms.  When one wheel is raised like by hitting terrain, the other is lowered, and the average of the two--buffered by the springs--is carried to the body (I know that sentence is terrible English, I can't think of how to explain it).  This also keeps fairly uniform track pressure, is rather light, easily removed and replaced, allows decent travel, and keeps the tracks from slipping.  No shock absorbers are needed, since the friction of the leaves sliding over each other dampens oscillation.  It is easy to see why this cheap and effective system was quickly copied and modified into various forms, from the Russian T-26 to the Czech 38t.  A downside to this system was that the leaves were prone to breaking either under fire or from sharp impacts.  Most tanks of the interwar period used small roadhweels to decrease individual point track wear and help keep from slipping a track, with this suspension system.

Rubber Scissor Spring
Much like the original Mini, the French developed a fairly standardized system of rubber springs used in their tanks, with (usually) a pair of wheels springing against each other.  A bit heavier, using a lot of rubber, it was, from the little combat experience it saw and from general analysis of the system, a fairly good approach.  Rubber has a natural dampening property, and is not prone to breaking like steel; however how it would have held up to things like flamethrowers or shellfire is questionable.  Either way, we will never know, but similar systems are used today in vocational trucks and bulldozers.
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Volute Spring
Now we get into the more-seen systems!  The volute spring was developed in the US, and is used only on US tanks.  A very durable system, it consisted of suspension arms and coiled strips of metal.  As the metal's layers glided over each other, it was a strong system and surprisingly resistant, while, due to the leverage the bogie arms provided, it allowed quite good travel.  Later variants (the HVSS) used the springs sideways, springing one wheel off another, to interconnect, which, combined with the advanced and well-insulated American running gear design, contributed to surprisingly long track life.  This system was also, like the leaf sprung bogie, easily removed if damaged by mines or shell fire, and was a bolt-on, modular solution.
A good video showing restoration of an early model volute spring bogie: http://www.youtube.c...h?v=E4-MkW4XMnI

Horstmann Bogie
If you drink tea and watch Top gear a lot, this might be a familiar sight for you.  The horstmann bogie was broadly similar to the US VVSS bogie, but used a coil spring instead of a volute spring.  This system was actually very comparable to torsion bars, being a tiny bit stiffer but also having better interconnection.  Interestingly, after torsion bars became the norm in the 50s, this system was retained on the Chieftain tank and several other vehicles.  Very simple, easy to replace, and a generally ideal solution in my personal opinion.  Show below is an early version, later versions had more travel and a shock absorber.

Aka "America fuck yeah".  Used a bell crank to transfer rotation of a springing arm's direction to allow very long springs to be used.  Christie acheived much success with this system, but the Soviets were the only ones who bought it.  They in turn copied it and his armor ideas and tracks, and threw them on the BT and T-34.  This system is by far the best for ride quality except for MAYBE hydropneumatic; some vehicles could ahve as much as a meter of suspension travel, enabling incredible speed.  Original Christie tanks also had a chain drive option, so they could run without their tracks on roads, because the concept of a dedicated tank transporter was apparently beyond 1930s America.  :Smile_sceptic:  A video of it in action: http://www.youtube.c...h?v=FWi1E-M9CtE

Bell Crank
Simple system with a pair of wheels on a bell crank, each bogie connected by a short arm and lever to a central spring running the tank length.  This version had actually too much interconnection, and, while having excellent travel, tended to make the tank sway back and forth a lot in motion.  Only the Japanese ever used it.  It is fairly heavy and large, and doesn't look particularly strong or durable.

Single Torsion Bar
A common, modern type of tank suspension, found today on many fast track layers.  A steel bar runs under the bottom of the tank and twists; connected to it is a short trailing arm, carrying a wheel.  As the wheels hit bumps, the bar twists.  This system is compact, light, provides good travel, is simple to manufacture, and is generally a good solution.  The downside is that tanks hit by mine damage may need to be cut open with a welding torch to repair--NOT fun, and a pain in the arse to do in the field.  Virtually all modern fast track layers use this system.  Tansk with torsion bars will have one sides' roadwheels slightly back from the other, noticeable upon close inspection, due to the packaging of the torsion bars.
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Double Torsion Bar
Only the Germans...this is a fairly complex form of torsion bar, where apparently one bar pivots, and one both pivots and seems to skew.  I can't explain it and only understand it partially.  Only ever seen on the German big cats.
Video of an explanation: http://www.youtube.c...h?v=aS3rP7rLJN4

The current "new thing".  Uses gas, whcih is very flexible and soft, as a springing medium in cylinders for each wheel.  Also has shock absorbers which are connected through pipes, making all wheels interconnected to each other and providing a very smooth ride.  Sometimes these shocks and the pipes are connected to the idler, as in the Chal2, to control tension as well.  This is a very complex but effective and generally light system that promotes track life, crew comfort, and low mechanical damage due to terrain.  The single drawback is that the system is not good in desert environments, as the sand can degrade the cylinders, hence its rejection from some custom-designed middle eastern tanks and the M1 Abrams.  It is slightly less durable and much more complex than torsion bars, but again, promotes track life and crew comfort, as well as making the tank very easy to maneuver offroad and a generally excellent system.

That's it, folks, the basics of most tank suspension systems.  Below I'm going to briefly touch on a few unique and experimental designs.

A short torsion bar on a bogie.  The bogie is free to pivot with one wheel at the end of it, and the other wheel is sprung.  Through the lever action, both wheels are actually sprung.  The torsion bar appears to be actually inside the bogie itself, geared to the arm.  Typical porsche, it's complicated but beautiful mechanically.  But a picture of it fully compressed is worth a thousand words [edit: link broke somehow] Look here: http://www.tiger-tan...re/history2.htm

A torsion bar system, but with interconnected hydraulic shocks like a hydropneumatic.  Only used by the Russians and in a few US arties I believe (not sure, don't quote me)

Belleville washers, little flat cones, were to be used on geared arms.  I can't find a good schematic, and can't really explain it well.  Used on the Swiss pz68 after the war and a few King Tigers.

Dog Leg
Specialized coil-sprung two-wheel pivoting bogie, a modern approach to the concept of bogies.  Very light, with a low center where the spring rests, springing against the hull at an angle and following the arm in its rotation.  Used on the American Ripsaw MS1 & MS2.  A similar system, with a single arm, is used on the Israeli Merkava; this has the TSAWS system where the coil spring can actually ride up off of the suspension arm, to allow the roadwheel to flop down unsprung held only by the shock down, as a method of increasing travel over very rocky terrain.  This prevents track slipping.

Axle Bogie
A pivoting bogie assembly with two arms with two wheels each and an idler.  Allows interconnection but no springing.  The entire assembly is suspended on a leaf spring.  Only ever used on Kegresse halftracks.  The system, with no leaf spring, is used on low-speed construction equipment to increase ground contact and torque.

Single Wheel Leaf
A short arm sprung by a leaf spring clamped to it.  Used on most variants of the Panzer II.  Also used nowadays on Bobcat company's crawlers.

Short T-bar
A short, half-length torsion bar.  Used on the soviet T-64.  Found to be very fragile as the bar had to be fairly soft to pivot sufficiently in such short space (more rotation per X amount of length), not used subsequently.

Others: if there are any, just give me a hollar.  If this thread is well recieved, I might do a thread on caterpillar track designs.  Until next time, have fun kids! --TheManWithNoName

Edited by TheManWithNoName, Nov 04 2012 - 13:27.

BlackCompany #2 Posted Nov 04 2012 - 12:10


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Good info, thanks.

Lert #3 Posted Nov 04 2012 - 12:44


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Great thread.

Your ferdinand picture isn't working though.

Blackhorse_Six_ #4 Posted Nov 04 2012 - 12:59


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Nice Job (+1)

The hydropnuematic systems with which I am familiar allow front-to-rear leveling, as on the Swedish Stridsvagn 103 (S-Tank) and [IIRC] the Japanese Type 74.

The MBT-70 and BMD-1 suspensions were designed for variable adjustment ranging from "high-ride" to "squat", but these adjustments were applied equally to both sides simultaneously. These were classed as "controllable" suspensions.

Suspensions of the Japanese Type 90, and Korean H2 "Black Panther"  allow for any combination of front-to-rear, side-to-side and corner-to-corner leveling.

The M1 Abrams series suspension is tortional, and anchored in fluid-filled rotary drums, which allow a greater range of swing on each road wheel arm than would the simple torsion-bar suspensions of the mid-WW2 and Cold War period. This is not a controlled system.

Mechanical "Leveling", a la the Korean K2, has been largely dismissed in most armies due to the mechanical complexity and resulting maintenance headache. Leveling is sufficiently accomplished through terrain training and the cant sensor integral to fire control systems where they are equipped.

lostwingman #5 Posted Nov 04 2012 - 22:52


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Ok...a couple of things make my head hurt.

A bell crank just changes the direction of a force. The R35 has a bell crank, most Japanese tanks used a bell crank, hell technically the HVSS is a bell crank and I think the Horstman is too (angle of force is changed from vertical to horizontal). Also the specific kind of suspension that the Japanese used was called the Scissor type (also referred to as the 'See-saw type').

Also I don't know if you can call the design weak if it supported a 45t design.
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This was the Horstmann that was mostly seen in WW2 and the 1930s, the one you posted is a later design.

You have a suspension up there called "Ferdinand"....there was never a suspension called "Ferdinand". The word you are looking for is "Longitudinal Torsion Bars". What most tanks with torsion bars have in game is Transverse torsion bars. Here is a description of the difference.


Torsion bars are connected to the frame in one of two configurations. Transverse torsion bars are mounted across the width of the car or truck, connecting to the frame close to the center of the vehicle. Longitudinal torsion bars are mounted along the length of the car or truck, connecting to the frame closer to the mid-point of its length. Regardless of where the torsion bar connects to the frame, it also connects to the wheel mount to provide suspension for the vehicle.

Belleville Washers, they are essentially angled washers put on a bar in a tube with one end attached to the wheel and the other to the tank. As the wheel goes up and down the angled washers compress against each other.

That's all I got for now.

MGP_34k #6 Posted Nov 05 2012 - 14:02


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Schematics of the Belleville washer suspension system planned on the E-series:


TheManWithNoName #7 Posted Nov 05 2012 - 15:15


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The Abrams has rotary shock absorbers, which are more efficient, it has nothing to do with the actual springing medium.  You CAN get the same travel with linear shocks, but long-travel rotation and linear shocks mounted on a static base don't mix well.  You get certain sections of travel giving you more damping than others.  To my knowledge, only a few tanks even now use rotary shocks as they are more difficult to manufacture, and rotary shocks have some issues with sealing usually when under such high pressures.  Curiously, this is also why rotary engines tend to be rarely found--high-pressure repeated-use long-life sealing of two-dimensional planes with variable friction wear was a colossal bitch and a half up until CAD really blew up, whereas a linear seal is very simple to design and manufacture.

View Postlostwingman, on Nov 04 2012 - 22:52, said:

A bell crank just changes the direction of a force. The R35 has a bell crank, most Japanese tanks used a bell crank, hell technically the HVSS is a bell crank and I think the Horstman is too (angle of force is changed from vertical to horizontal). Also the specific kind of suspension that the Japanese used was called the Scissor type (also referred to as the 'See-saw type').  It's listed as "bell crank" in most resources.  Not the name I would have chosen.  "Coil-spring tube twin bogie lever arm" just doesn't have the same ring to it though.

Also I don't know if you can call the design weak if it supported a 45t design.  It was prone to breakdown and battle damage on five and ten ton tanks.  I can't see it practically being used on a 45-ton.  The vehicle you posted has no real combat service history, so we'll never know how it would have performed.  I see a lot of travel and a lot of breakdown, though.

This was the Horstmann that was mostly seen in WW2 and the 1930s, the one you posted is a later design. Not necessarily, while early war saw much of the version you posted with a raised "knuckle", a few pre-war light tanks had the version I posted.  They're minute geometry differences.

You have a suspension up there called "Ferdinand"....there was never a suspension called "Ferdinand". The word you are looking for is "Longitudinal Torsion Bars". What most tanks with torsion bars have in game is Transverse torsion bars. Here is a description of the difference.  BMD-1 is not a suspension, either.  But the systems were used only on one vehicle afaik.  The suspension concept on a T-64 is rarely duplicated, but has been seen in other places periodically, such as certain industrial machines (it's a special softener than normal torsion bar, short t-bars aren't exactly the same per se), so calling it "T-64" wouldn't be necessarily correct.

Belleville Washers, they are essentially angled washers put on a bar in a tube with one end attached to the wheel and the other to the tank. As the wheel goes up and down the angled washers compress against each other.  Yup.  I was hoping to get a schematic of the bogie itself, it was provided already though.  Good work MGP_34k.  I couldn't find it when i searched but i used to have it on my old computer.

Also, forgot to amend to original article: volute springs are found on US tanks only, save one unusual example--the Russians used them as bump stops on some vehicles, such as the BMD-1.

Edited by TheManWithNoName, Nov 05 2012 - 15:18.

The_Chieftain #8 Posted Nov 05 2012 - 19:51

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Double torsion bars are not unique to Germany. A modern version actually puts one torsion bar inside another, the other bar being actually a hollow tube, the anchor point being on the same side as the wheel it's anchoring. It was being considered as an upgrade to the M1's suspension.

lostwingman #9 Posted Nov 05 2012 - 20:16


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Longitudinal Torsion bars were placed on virtually every tank Porsche designed after the VK3001P.

Also really, that's what the Japanese style Bell Crank was called. They were designed by Tomio Hara and pretty unique to Japanese designs and are pretty consistently referred to as see-saw type or occasionally scissor type. Since that is the way Tomio Hara calls them, I'm going to go with that over ww2 drawing websites. Again most these suspensions technically use a bell crank as all a bell crank is is a crank that changes the direction of a force. I don't see how you'll give the French it's unique name for their bell crank bogies but not the Japanese. Also everything I've read has said the suspension was pretty good for the off-road necessities of rural China to the point that the Army kept putting new designs on the back-burner.

Also the Maus used volute springs as well. Of similar style to the M6's design.

Also what MGP posted was the mounting for the actual Belleville washers, how the Belleville washer part of the suspension would look like is what I posted.

Edited by lostwingman, Nov 05 2012 - 20:23.

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