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Tracks Offroad.

Low ground pressure is important offroad in snow, sand or muddy conditions. Nothing can equal the low ground pressure achieved by tracks offroad, not even the widest swamper tyres (tires).

Halftracks

International M14 Halftrack picture

The advantages of tracks in snow, sand and mud has been realised since at least the first World War when tracks were fitted over the rear wheels of 6x4 trucks, and of course the first tanks were also fitted with tracks.

Citroen built a number of successful halftracks which took part in major expeditions in the 1920's and 1930's.

This M14 halftrack (left) was built by International for the American Army during World War Two.

Halftracks are usually based on standard trucks or four wheel drives and so can share mechanical components with them. They steer like ordinary trucks and so do not need the complex transmission of a fully tracked vehicle. This also reduces the need for special driver training.

Cuthbertson Track Conversion

Cuthbertson tracked Land Rover picture

A special purpose tracked vehicle is obviously an expensive proposition while conversions of regular four wheel drives can be cheaper.

In the 1950's and 1960's, the Cuthbertson tracked Land Rover conversion took a standard Land Rover and fitted demountable tracks to it. The tracks are carried on a substantial subframe to take the stresses and strains off the standard wheel hubs and axles.

A back of the envelope calculation shows the low ground pressure advantage of tracks. Assuming a four wheel drive weighing three tons (6000 lbs), a wheelbase of 90" and a track width of perhaps 20" gives a ground pressure of about 1.5 lbs/sq"; 1.9 lbs/sq" is claimed for the Cuthbertson. A 12-stone man exerts a ground pressure of about 6 lbs/sq" in comparison and the best that a multi-wheeled vehicle such as the 8x8 Esarco can manage is something like 9 lbs/sq".

Although the tracks give impressively low ground pressure this is not everything offroad. The step-up ability of a wheeled vehicle depends largely on the tyre diameter. For something like the Cuthbertson this translates to the diameter of the leading wheels on a bogie - about the same as a regular tyre. Army tanks in contrast achieve a huge step-up ability by having the leading edge of the tracks slope upwards from the first load-carrying wheel to a drive sprocket or idler. This is not practical on a small four wheel drive.

Bolt-on Tracks

Pictures a Toyota LandCruiser with tracks

While the Cuthbertson's tracks were, in principle, removable this was not some five minute operation. The idea of simple bolt-on track units is attractive as they can be towed in a trailer behind a standard four wheel drive to the snow or the swamp where the switch to track power is made. Manufacturers such as Mattracks have made such gadgets.

These tracks (left) were being demonstrated at the 1996 Perth 4WD Show on a Toyota LandCruiser 80series. The tracks are under test by Toyota Accessories division. They weigh in at just 85kgs each and can be fitted in about an hour by one person with a good jack. The main question about these devices must concern the ability of the four wheel drive's standard steering and wheel hubs to withstand the forces generated by the tracks.

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Full Tracks

Where snow is deep, soft and permanent, a fully tracked vehicle is the only way to go. Volvo make the BV202 which is used by the British Army. The Australian Antarctic division uses Hagglund machines.


History

Gernot writes in with some more history:   The German Daimler truck company had been contracted to built a 4WD heavy car for the colonial army then fighting in German south-west Africa. Since the vehicle was found suitable a 4WD truck version was commercially built. These 4WD trucks were well liked by the Allieds - the victorious Allies took nearly all 4WD Daimlers (and Ehrhardts) in 1919.

The Portuguese bought one of these trucks for their Guinea. And all went fine until the rainy season came. The truck sank in the mire. It was sent back to the manufacturer who built the chains of a Holt tractor onto each side in place of the back wheels. Afterwards the buyer took it back - the arrangement worked. But there were no further orders. The Daimler company even mislaid the plans - so when they began to build half-tracks again in 1916 they had to start anew.

The French experimented with tracks, like the Germans, but with "rubber bands". The deserts of Tunesia quickly ruined the rubber chains of a Peugeot car. The inventor of the French halftrack system, Armand Kegresse, went to Russia. There he became chief chauffeur of the Czar. The Czar had a fleet of cars - but could not use them because of the mud and snow. Kegresse transformed the car pool of the Czar into halftracks - much to the delight of the owner. The bigwigs of Russia like the rubber halftracks way down the ages. Kegresse must be counted as the first successful cross-country automobilist since he perfected a design, that permitted a single chauffeur to operate a car in difficult terrain.
- Gernot [11/'00]

See Snowtrac and for a bit of fun, see [this]!


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