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Tank wheels


Scrapper_511

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The teeth on the drive sprocket engage the end-connectors or ends of the track links (the end connectors form a step beyond the end of the track).

They lift the track from under the rear road wheel, forcing the tank to roll forward. The roadwheels spread the vehicle weight over a number of track links (on firm ground more-or-less the same as the number of roadwheels, on softer ground the sinkage spreads the load over a few more links around each wheel, but it takes quite soft ground and high track tension to approach an even pressure over the whole contact area).

The teeth on the track itself are to minimise the occurrence of thrown tracks - they pass between the roadwheel pairs (or to both sides of a single on a light AFV). Some older types (T34 IIRC, used the track teeth to engage recesses in the centre line of a 'toothless' sprocket).

The Idler serves to increase the 'effective size' of the wheels to allow a much larger step to be climbed than if the track wasn't lifted at the front end... Commonly there is also an adjustment for track tension, obtained by moving the Idler fore-aft a few inches. This can reduce vibration noise and wear on hard surfaces (normal/slacker tension) or improve soft ground performance (higher than normal tension). Some newer vehicles can adjust the track tension hydraulically from the driver's station.

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And just for the historical record, one must also recall the Christie-type vehicles such as the BT-5 which did have powered roadwheels, so that they could run without tracks.

NTM

Weren't the road wheels driven by a chain attached to the drive sprocket?

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Unsure of the details, but I suspect this may be related to the central drive-take-up of the T34 toothless sprocket*.

Combining this with a similar 'toothless' drive on the last roadwheel would allow 2wd for the 'tracks-removed case'.

Not that the vehicle could continue movement immediately after shedding a track, but that road movement could reduce the wear and internal friction when driving on a flat/firm surface by replacing the track with a minimal profile drive to the roadwheel tyre.

I'll try and find out more.

*However, the T34 no-longer had a drive take-up on the roadwheels despite the Christie origin.

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