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Interleaved wheels and front wheel drive advantages


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del500044138 #1 Posted 23 February 2012 - 02:01 PM

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Hi all,

I was wondering why the German army in WWII loved interleaved wheels on most of their tanks and why most tanks (and US tanks) used front wheel drive, while the Russians favoured rear wheel? I've read up a little but it seems the disadvantages are more numerous than the advantages which seems odd considering the Germans made huge technological strides throughout the war, so I must be missing the obvious.

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Ironclad #2 Posted 23 February 2012 - 02:14 PM

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might be wrong on this but...shorter tanks! the shorter the tank, the less armor is needed to cover the flanks--->less weight
German engines of panther and tiger series specialy designed to be short too.

BrianDuffy #3 Posted 23 February 2012 - 02:18 PM

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AFAIK interleaved wheels spread the weight more evenly and reduce ground pressure a bit allowing heavier tanks and greater stability. They may also have improved the ride a bit allowing for more accurate fire on the move, although that would have had only a minor effect I would say.

My best guess about USSR using rear wheel drive would be the cheapness and technical simplicity of that design. I don't believe there is any inherent benefit to either system. It may be that you stick with what you know and USA/German started with front wheel drive and just stuck to it.

Edit: one thing to bear in mind is that despite the German "high level of technology" it was the USSR which developed sloped armour first and sometimes, as USA found during the Vietnam war with Phantoms etc, it is possible to get a bit carried away with your supposed "technological superiority" and overly complicate things which I think may also have been a factor with later German tank design

Bombastikus #4 Posted 29 February 2012 - 04:20 PM

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View PostPere_Ubu_Roi, on 23 February 2012 - 02:18 PM, said:

My best guess about USSR using rear wheel drive would be the cheapness and technical simplicity of that design. I don't believe there is any inherent benefit to either system. It may be that you stick with what you know and USA/German started with front wheel drive and just stuck to it.

My understanding is that a rear wheel drive is inherently a bit better since it pulls from the underside when driving forward instead of the from the upper side, therefore reducing stress on the tracks enhancing their lifetime. (Altough this is probably only a small factor in view of the overall quality of a suspension design.)

Today most tanks have rear wheel drive mainly because engine and gearbox form a single block which can be completely removed in a very short time. In WW2 however, the gearbox was a huge piece of equipment and nowwhere near as reliable as gearboxes today, prone to breakdowns and with relativly short lifespans (this is pretty much true for all tanks of ww2).

Therefore, german and US engineers prefered to seperate the engine block and the gearbox for easier maintanance and changing and for a more evenly distributed weight. As for the USSR, either their engine/gearbox design was so small and superior that it didn't matter or they simply gave a damn about a single tank as long as three others roll from the production line in the time it took to change a gearbox.

Kyphe #5 Posted 10 March 2012 - 03:15 AM

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you have several issues at play, if you have an all around armored tank then having an engine and gearbox at each end of the tank makes for even weight distribution, but if you have extra heavy frontal armor then having both engine and gears in the back helps balance the tank out.

A rear gearbox also allows for a sharper angle to the slope of the front hull, and removing the drive shaft allows the tank to be lower

A frontal gearbox makes for an easier driving situation and a short tank is more square which makes for better turning.

have a look at the tigers transmission

http://www.alanhamby...nsmission.shtml

the Germans did experiment with rear drive units, the DB the 3001p the vk4502A were rear designs and the E75 was most likely designed rear drive even if some argue against it

Donken86 #6 Posted 20 March 2012 - 06:30 AM

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First question is a pretty easy one, It is for a smooth ride, Look at youtube of panthers driving around and see how very very smooth they go over bumps etc (almost looks like modern air suspension). There is a few downsides thou. First it is a pretty heavy setup (it weights alot) and second becuase the german tanks where pretty short they needed to make it compact therefore the wheels are interleved. And that made changing inner wheels a hell.

Second one, this is alot harder and "experts" are still arguing about this one, But we will to 110% never know why really. There are bad and good things with both of them, But from my own ideas and logic it was a matter of size for the tanks. They could made the tanks alot shorter this way. Ironclad explains it pretty good. And also the weight distribution is better. The centre of mass is pretty much in the middle even with the long guns they have, If they would have made a rear wheel drive with those big turrets and long guns (they would have been moved forward) they would have been very front heavy and uneven centre of mass.

But still the biggest discussion about this is if you gain or loose anything with having the drive sprockets in front or rear. The tracks are getting pulled or driven. That is a hard one. The logic says with a driven track (transmission front) you dont get so much stress. Think of 1 meter long rope. pull on each end 1 meter apart, the stress is even distributed throu the whole rope and the rope also helps with its momentum to even reduce stress further. Now take a rear drive, take this same rope and pull with 1dm apart (last roadwheel to drive sprocket). Wich one stresses most under heavy duty? Wich one brakes first? I dont know.
And you also need to think about how easy it was to throw a track (they fall of the wheels) Logical it says that rearwheel drive should be better but when i watched a few simulations of front wheel drive im not so shure about that anymore. The first pair of roadwheels is kind of steering the tracks so they cant fall of that way. No matter how much you turn around. With rearwheel drive you have a longer way of a "loose" track that can twitch and bend etc. But then you dont have the drivin force instead, So i have no idea but its worth thinking about :D

Vlevs #7 Posted 31 March 2012 - 09:14 PM

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Part of the rationale for interleaved wheels was Germany's lack of rubber. Germans decided to improve ride on all-steel wheels by making a large number of large wheels. Both features improve drivability and reduce wear, but complicates maintenance and broken wheels are much harder to remove and replace. Wheel arrangement doesn't effect tank length, because hull is only as long as necessary for interior space.

German 'school' of tank building preferred centrally-mounted turret with minimal gun overhang; Soviet tanks have turret in front and large gun overhang. This means gearbox is placed in front where it's also easily operated by driver. One reasoning I've heard is that front sprocket gives better tractive effort, but I don't understand why. Driveshaft running under tank turret increases tank height which adds weight, and part of the reason why Germans tanks are much taller than Soviet ones.

Gearbox seems to be very 'dense' component, which determines much of tank's weight distribution. T-34 and T-54 have rear drive, but even with front turret, overhanging gun and heavy glacis plate front wheels are positioned further apart than rear wheels, which indicates centre of gravity is rearwards. IS-4 seems to have a 'notch' on the back to house gearbox, drive sprocket and a pair of road wheels.

View PostKyphe, on 10 March 2012 - 03:15 AM, said:

the Germans did experiment with rear drive units, the DB the 3001p the vk4502A were rear designs and the E75 was most likely designed rear drive even if some argue against it
Source for this? You can clearly see that rear-drive tanks you mentioned have turret in front like in Soviet tanks, while front-drive German tanks have middle turret. E-75's layout was heavily based on KT, having middle turret and front drive.

Bombastikus #8 Posted 02 April 2012 - 10:29 PM

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View PostVlevs, on 31 March 2012 - 09:14 PM, said:

German 'school' of tank building preferred centrally-mounted turret with minimal gun overhang; Soviet tanks have turret in front and large gun overhang. This means gearbox is placed in front where it's also easily operated by driver.

True. Actually I read that was one of the reasons, the PzIII was initially only refitted with the L48 5cm gun, because they feared that the already developed L60 was to long and unwieldy.

Having served as a Leo2a4 gunner I can say that gun overhang can be problematic with tank-unfriendly enviroment, like woods etc....so I guess considering france and germany this is certainly understandable. Russia is much more open so that wouldn't be really a problem there, I think.

V0ILA #9 Posted 03 April 2012 - 01:25 AM

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depends on what part of russia you are fighting Bombastikus

the steppes are open but there is plenty of forest in russia. i guess that most of the fighting would have taken place over the steppes into eastern germany if "ww3" had actually happened

i guess its one of those rl vs in game situations you encounter, front mounted turrets are great in game because of the 90degree angles we encounter a lot, (buildings/rocks/other tanks) with out having to worry about hitting trees etc that irl tankers/designers have to worry about, (i am looking at you revolver system)

Schiltron #10 Posted 03 June 2012 - 09:11 PM

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Germans made extensive testings of both front and rear driven tracks...

the plus and minus were minimal

plus for front wheel drive...
lower wear and tear of the drive sporcket wheel because the track has more time to get clean befor it reach it
short way of gearbox shifting system
front mounted gearbox could be designed longidutinal (not much different to well known truck gearboxes)
the driveshaft through the crew compartment could easly be used to power the turret travers system
additional crew protection
easy access for fine adjustments of the shiift system

minus
drive shaft through crew compartment means in average 10cm higher hull...
cost space in the fighting compartment
needs a large removable plate over the driver radio operator to get replacet
slightly higher risk to jam the track while backing up
slightly higher risk to get immobile if hit at the track from the front

rear wheel drive
plus
more space in the crew compartment
gearbox could be more easy replaced
lower hull because no drive shaft goes through crew compartment
allows free design of frontal armor

minus
higher wear and tear on the drive sporcket wheel because of mor dirt on track
needs long gear shifting system that could pretty easy jam by shocks if tank gets hit
adjustments at the shift system needs more work
shiffting needs much more strengh which reduce ´driver performance quicker
adds no additional crew protection


as a final result from the tests the germans saw no advantage disadvantage of both layouts... they choose front wheel drive because f the simpler gearbox design layout and the abilty to place the turret into the center of the tank which gave the tanks a good balance

Edited by Schiltron, 03 June 2012 - 09:13 PM.


Schiltron #11 Posted 03 June 2012 - 09:16 PM

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oh and interleaved wheel layout was choosen because form the avaible materials for the Germans it was the only solution to build heavy tanks with good suspension and nicely balanced groundpreasure spread over the whole track. That benefits outweight the drawbacks of higher maintenance and cleaning work

Cabal668 #12 Posted 26 June 2012 - 10:17 AM

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Hello, i hope this topic is not dead already. And sorry for my bad english, i had few training over the last year ; )

The question about why FWD was used is like comparsion of FWD Cars or RWD Cars. Both have plus and minus.
When i was in the German Army i was a Tankdriver and trained on the Leopard 2A4 to Leopard 2A6. In the Driving School for that Tank we learned much about this Tank and advatages and disadvantages.
One of the Points to use FWD is, that you can't "throw" down the Tracks of your Frontwheel when driving a narrow curve with low speed. If you do so with a RWD you will loose your Track, even if not hit by an Enemy and you need about 1-2 hours to put it back on the Tank. In German its called "Kette schmeißen" and i had it once while drining to heavy ground, which is worst case that can happen ; )
But the Bonus of RWD is, that you can't loose your Tracks while driving backwards even though you drive very slow.
That's why they use FWD still. The German APC Marder has it, so there is more space in the back and the Tank is able to maneuver very quick while driving forward not having the problem of loosing a Track.

The Rest of the Points others wrote are also right (smaller Engine compartment, short gearways, ...)

Ah, one thing more. The Panther is not driving so smoothly because of FWD, its because of the suspension they used. Still today they use tension Bars for the suspension of Tanks.

I hope you understand the Point i mensioned.

Cabal

tigerstreak #13 Posted 04 July 2012 - 09:43 PM

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will front drive, tension the top of the tracks +make them less likely to come off the top rollers?
while the lower part of the tracks are under road wheel weight +not going anywhere...

Edited by tigerstreak, 04 July 2012 - 09:44 PM.


kogybear #14 Posted 31 December 2013 - 04:41 AM

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Sorry to hop on a old thread, but the answers are quite simple.

 Why interleaved road wheels:

 

1) The larger the wheel (of any ground vehicle) the lower the rolling resistance.  The Tiger and Panther tanks were very heavy and on the verge of being under-powered, the Tiger I was twice as heavy as an M4 but only had 50% ore horsepower, so anything to decrease the rolling resistance was required.

 

2) They require a large number of torsion arms to support the weight of the vehicle.  With a Tiger a non-interleaved design (eg, the Porsche design) would only have half as many suspension arms, thereby doubling the load on each arm.  Which means each arm would weigh more, starting an upward weigh spiral.  There is the added benefit that each road wheel is loaded lower, and therefore, should, in theory, last longer.

 

The increased number of suspension arms also gives a better ride, as each spring can have a lower spring constant.

 

The ground pressure IS NOT a factor.  The track always maintains contact with the ground, therefore the ground pressure is the length of the ground contact, times the track width, whether you have 16 road wheels or 24 per side.  What it does is evens out the stress on the track.  With three wheels spreading out the force evenly across the track, you have less bending.  (Imagine a three foot long board on soft mud, then drive a car over the center of the board, the board will likely bend and break in the middle.)  Once again, these allows for a lighter track design.  Not only does this reduce overall weight, the track is "unsprung" weigh, the lower the unsprung weight, the better the vibration isolation, the better the ride.

 

Why the drive sprocket in the front?

 

Power/strength requirements.  With the drive sprocket in the front, when you step on the gas, you pull tension in the entire upper track length and compress the idler slack, then it picks up the last track block on the ground which pushes on the last road wheel and shoves the vehicle forward.  With a rear sprocket, the engine must immediately pick up the last track block on the ground and start the forward motion.  Rear sprocket designs will accelerate faster, but require more power and much heavier duty gears, pinions, etc....which means more weight.  The T-34 did what it did for the same reasons rear drive in almost universal today, the engine/transmission/steering pack is one compact unit, and they didn't have the weight restrictions the Tiger designers did.

 

Henschel designed the lightest possible chassis design so they could used all that weight saved in armor and firepower.  The design trade-offs were increased maintenance and complexity, but these weren't show-stoppers as they continued to build, maintain and operate Tigers and Panthers until the very end.

 

Why doesn't anyone do it today?  Because the advantages of better metals and more powerful engines offset the drawbacks.  An M1 would probably require 2% to 5% less horsepower if it used 36 inch interleaved road wheels, but would that be worth it?  Only if the largest available engine you had produced 1400 hp not 1500 hp.....



Vlevs #15 Posted 06 January 2014 - 09:18 PM

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View Postkogybear, on 31 December 2013 - 05:41 AM, said:

Sorry to hop on a old thread, but the answers are quite simple.

[...]

 

That's quite a lot of claims I've never heard before. Can you substantiate them somehow?

 

1) Rolling resistance of larger wheel was not a factor, given how little of total resistance wheels produce in a tracked vehicle - track itself is main cause. In addition, T-34 got away with very large road wheels in non-interleaved design. Rather, the goal seemed to minimize relative wheel travel when moving over uneven terrain. And does doubling number of wheels really decrease rolling resistance? I'd say not.

 

2) Panther's hp/ton was similar to M4 Sherman's. Tiger was a heavy tank, and wasn't expected to be as mobile.

 

3) How does doubling number of torsion bars save weight versus doubling capacity of each individual torsion bar? There doesn't seem to be any weight advantage one way or another.

 

4) Front drive having better weight efficiency. Rear drive might have slightly higher starting torque requirement, but with front drive you have driveshaft running through entire length of the tank. In addition, driveshaft running under turret requires turret to be installed ~20 cm higher to keep constant interior height. This causes a substantial net increase in tank weight.

 

5) Tiger's drivetrain having more strict weight constraints than T-34's. What the... Tiger design process overran its weight goals several times over. The only drivetrain design constraint of Tiger was its short engine bay. Apart from engine I've never heard of any kind of serious design push to save weight in German WW2 tanks. Case in point, part of German late-war designs' unreliability was because their drivetrains were designed for lighter tanks altogether. It is specifically lack of weight restraint that hampered them.

 

6) Finally, you suggest modern tanks would've adopted interleaved roadwheels had there been only 1400 hp (lol) engine available. No way, no how they would do that, regardless of power available. Not that it would save any. How did you come up with the "2% to 5% less horsepower" figure anyway?

 

Personally I regard interleaved road wheels and rear engine + front drive combination design quirks that were repeated more out of habit than for any real benefits. Given that both design features died soon after WW2 suggests this to be the case. AMX 50 is an exception and only because French wanted to save time when designing a heavy tank ASAP, and took from German heavy tank research what they could, given that it was freely available.



labixiaoxin #16 Posted 25 January 2014 - 02:04 AM

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[edited]


Edited by Petruzzi, 26 January 2014 - 12:10 PM.
This post has been edited by a member of the Moderation Team, due to inappropriate content. An official notification has also been sent.Petruzzi


Bombastikus #17 Posted 15 February 2014 - 01:25 AM

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View Postkogybear, on 31 December 2013 - 04:41 AM, said:

Sorry to hop on a old thread, but the answers are quite simple.

 Why interleaved road wheels:

 

1) The larger the wheel (of any ground vehicle) the lower the rolling resistance.  The Tiger and Panther tanks were very heavy and on the verge of being under-powered, the Tiger I was twice as heavy as an M4 but only had 50% ore horsepower, so anything to decrease the rolling resistance was required.

 

No...rolling resistance had nothing to do with it. One reason was certainly that larger wheels deal better with rough terrain but the main factor for larger wheels were rubber. The germans had made bad experiences with the small roadwheels on the PzIV since considering the quality of the rubber back then, they didn't last long enough. The same is true for the PzIII which had an excellently designed running gear, but also the lifetime of the roadwheels was to short. One solution to fix this was simply to bring more rubber onto the track. This worked quite well on the panther (and was later only replaced with the rubber saving steel roadwheel because of shortages) but didn't work quite so well on the Tiger H because it was just to heavy for the then available rubber-technology.

 

2) They require a large number of torsion arms to support the weight of the vehicle.  With a Tiger a non-interleaved design (eg, the Porsche design) would only have half as many suspension arms, thereby doubling the load on each arm.  Which means each arm would weigh more, starting an upward weigh spiral.  There is the added benefit that each road wheel is loaded lower, and therefore, should, in theory, last longer.

 

The Porsche had a completely different suspension system to the Henschel Tiger. It coupled two roadwheels in a scissor-like contraption which was externally spring loaded with a relativly short longitudal torsion bar. Porsche patented the design and it was used on pretty much all his tank-designs (vk3001p, tiger p, ferdinand, some Jagdtiger prototypes) but from what I gather it wasn't realyl that good.

 

However, saying that the Tiger (and by extention Panther, KT etc.) had a weight advantage because they were able to make torsion bars, suspension arms etc. lighter you are quite mistaken. The oppositte is true and the choosing suspeion-type is one of the reasons those tanks were relativly heavy. (However, with a top notch suspension, especially the panther). There were attempts to use the Porsche desgin suspension system on the Jagdtiger, one reason being that it would be about 2 tons ligther.

 

 

 

The increased number of suspension arms also gives a better ride, as each spring can have a lower spring constant.

 

That is correct!

 

 

Why the drive sprocket in the front?

 

Power/strength requirements.  With the drive sprocket in the front, when you step on the gas, you pull tension in the entire upper track length and compress the idler slack, then it picks up the last track block on the ground which pushes on the last road wheel and shoves the vehicle forward.  With a rear sprocket, the engine must immediately pick up the last track block on the ground and start the forward motion.  Rear sprocket designs will accelerate faster, but require more power and much heavier duty gears, pinions, etc....which means more weight.  The T-34 did what it did for the same reasons rear drive in almost universal today, the engine/transmission/steering pack is one compact unit, and they didn't have the weight restrictions the Tiger designers did.

 

No...power strength requirments were not really a factor. Drive sprocket in the front or in the back have both advantages and disadvantages but those were pretty much equal. (Perfect example were the two Panther designs from MAN and Daimler Benz. The DB model had a rear drive sprocket, MAN a more conventional front mounted one. Since the advantages and disadvantages of both systems were pretty much the same, this difference did not enter the equation when they were deciding on a production model.  But the main factors seem to have been that with a front mounted sprocket you can change gears directly on the gearbox (easier for the driver) and the weight-distribution is better allowing for a more centrally mounted turret.

 

However, as I said, if the Daimler Panther hadn't other, more glaring issues (smaller turret ring diameter, no turret fit for mass production etc.), they could just as well have built a Panther with rear-drive sprocket.






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