Why Half Tracks?

[jaguh]

I understand that most (all?) of the German half tracked vehicles disengaged and braked the inner track once a certain steering angle was reached. The same way a full tracked vehicle steers.

Why then add the complication of a fully functional front axle with steering linkages, brakes, suspension, the works?

Why not just add one or more road wheels and some links? That should result in a cheaper vehicle with improved off-rad performance, like later in the war the RSO. (but then we also have the Schwere Wehrmachtsschlepper around then?)

Obviously there must be a good reason as everybody(?) fielded half tracks. Except the Americans replaced the complication of the steering wheel - steering brake connection with the complication of a front wheel drive.

I can only see better? road handling at higher speeds as a reason for that expensive solution.

This is purely guessing on my side as I have never driven any tracked vehicle myself (low speed or high speed).

Anybody here with personal experience driving a half track? Or any tracked vehicle faster than an earth mover?

rgds

Jaguh

[jaguh]

Just saw in the thread "Interesting eBay Pictures" a post war development of the RSO.

Lo and behold, with a front axle added! Just a simple pivot plate steering, but a wheel steering nevertheless!

Again, wheel steering must give a payback justifying the added expenses in manufacturing and maintenance.


Jaguh

[mrcrazy]

Any tracked vehicle is constrained by the ratio of the length of track in contact with the ground and the distance between the track centres. This ratio is a maximum of 2:1 or steering becomes difficult. There is a practical width limit of around 8 feet/2.4 metres, to operate in an urban environment. So, if the track centre distance is 7 feet/2.1 metres, the track length in contact with the ground can only be 14 feet/4.2 metres. Stick three feet/one metre on either end for sprocket and trailing wheel, and you have a box that is 20 feet long/6.2 metres by 8 feet/2.4 metres. Stick an engine, gearbox, cooling system and transmission inside that box and there’s not much space left.

However, if you sit the driver and front passenger/commander on top of the transmission, connecting the front drive sprockets, gearbox sticking out in front with an engine in front of that, and radiator at the front of that, you can stick a pair of wheels, (preferably driven) under the engine and you have a 20 x 8 foot/6.2 x 2.4 metres space behind you that only has the transmission intruding.
Limit on British train load width is ten feet/3.1 metres; that’s why British tanks were so badly cramped in WW11. Most MBT these days are around 12 feet/3.7 metres in width.

[Hoist40]

There is also the transmission/final drive which is needed to steer the vehicle. They range from very simple clutch brake to more complicated expensive systems. The simple systems have lots of wear/tear and inefficiency when operated and with a full tracked vehicle every small adjustment in direction you need to engage the system. By adding front wheels most of the turning is controlled by the simple wheel steering while the track steering needs to engage only for steering tight turns or really bad terrain.

The American armored and German unarmored half tracks did away with track steering and just used a regular truck parts with added track unit

Another neat way of reducing the wear and tear on tracked vehicles brakes and clutches was the Bren Gun Carrier. The British version had a wheel which operated a arm which moved the front track wheels in and out bending the track so that small turns could be done without engaging the brakes/clutches.

[jaguh]

mrcrazy, Hoist40

thanks for your explanations, they complemented each other nicely. I knew there had to be convincing arguments for the steerable front axle.

The arguments for the track part should be easier to come up with: lower ground pressure, better traction, lower centre of gravity, more cargo space as compared to a 6 or 8 wheeler.

Modern development seems to favour the all wheeled vehicle though. A quick Google research showed them to have a wheel base - width ratio approaching 2.5 (I am guessing here as only the overall length and width is given in the Wikipedia articles, typically 7m / 23' length by 3m / 9.8' width). But this should not pose any problems with all-wheel steering.


rgds

Jaguh

[sebas379]

Pure speculation on my part here, but my theory is this.

A vehicle with only wheels has trouble traversing rough ground, that's why tanks have tracks.

Yet a vehicle with tracks isn't as quick and maneuverable as something with wheels, especially on roads.

The halftrack offers the best of both worlds, being able to quickly move troops and supplies from one place to another when needed, while also being able to support other troops when operating in the countryside.

The question that now comes to my mind is this: Some halftracks (like the German ones) had wheels up front and tracks in the rear. But I do recall seeing at least one vehicle somewhere that had it reversed. I can't recall what vehicle, nationality or anything, but what would be the reason for that?

[ChristopherPerrien]

Lack of differential steering for the tracks, They needed wheels as a rudder. A failed concept. The MK1 tank of WWI is prolly the best example, even though that was a "tank".

Half-tracks represent a trade-off between traction and maintenance/fuel efficiency is all. Later armored half-tracks needed the extra traction to handle their own weight and to have some minimum towing capacity.

[Kocur]

There were two distinctively different types of half-tracks, built for different reasons.
Basically, German ones were tracked vehicles with steering wheels added. The idea was to use wheels for gentle turns in which no energy would be lost to differentiate speed of tracks. Not a bad idea when one has no cheap track steering units which would make loss of energy during turn of tracked vehicle negligible, and all you have is braked differential or clutch and brake at best. In practice, when driver of German half-track turned steering wheel, at first only front wheels would turn. If he turned steering wheel further, brake at one side of differential would engage and make one of tracks slow down. This meant losing energy by heating the brake, hence worse fuel economy. Another approach to the the same problem was used in British Carriers, where for gentle turns tracks were warped and only for tighter turns further turning of steering wheel engaged a brake on differential.

The other kind of half-track was represented by French and US types. These were basically wheeled vehicles in which rear wheels were replaced with tracks to minimize ground pressure, improve traction etc. - to improve off-road capabilities in general. The only mean of turning were front wheels.

The difference in the approach is visible externally - in German half-tracks a gap between front wheels and tracks is much smaller than in, say, US half tracks. I mean, a vehicle similar to Sd.Kfz. 251 would probably have excessive turning radius if front wheels were the only mean of changing direction.

[ChrisDR68]

Had the war gone on into late 1945 or even 1946 I wonder if the Germans would have dropped halftracks altogether and gone with fully tracked armoured personnel carriers.

The advantages would have been better protection for the men inside as it would be fully enclosed. Better traction over rough or muddy ground and if based on an existing panzer suspension better in terms of maintenance and spare parts.

The obvious hull to transform into this type of vehicle would have been the Panzer III/IV that was used for the Nashorn and Hummel. With the engine in the centre of the hull and the final drive and transmission at the front it leaves the rear free as an enclosed compartment for panzer grenadiers.

The imaginary Sdkfz 350 gives a pretty accurate rendition of the type of vehicle I'm describing.

[Christian Ankerstjerne]

They were planning to do switch to fully-tracked APCs, yes.

[Sleipnir11]

Basically, German ones were tracked vehicles with steering wheels added. The idea was to use wheels for gentle turns in which no energy would be lost to differentiate speed of tracks. Not a bad idea when one has no cheap track steering units which would make loss of energy during turn of tracked vehicle negligible, and all you have is braked differential or clutch and brake at best. In practice, when driver of German half-track turned steering wheel, at first only front wheels would turn. If he turned steering wheel further, brake at one side of differential would engage and make one of tracks slow down. This meant losing energy by heating the brake, hence worse fuel economy. Another approach to the the same problem was used in British Carriers, where for gentle turns tracks were warped and only for tighter turns further turning of steering wheel engaged a brake on differential.

It is said that CleTrac was equpped in German half-tracks from the lightest Sd.Kfz. 2 Kettenkrad to the heaviest 18t Sd.Kfz. 9 “FAMO”. The CleTrac is a controlled differential steering system that involves braking on idler of the epicyclic gearing to change the power input into a single track. It does not resemble clutch braking steering. Just wonder if this is valid information.