The Science

Critical for this week's challenge was the ability to employ effective gearing. The teams needed to be able to select high gearing for the sprint and low gearing to get the torque needed to pull a heavy load from a stationary start.

The Subs' gearing design gave them the best chance of success. They had a multitude of gearing options on the mountain bikes, as well as all of the Land Rover's gears to choose from. This meant they could gear right down for the off and then step up once they had got moving.

In comparison, the final drive for the Chariots was not geared low enough and the tiny rail wheels meant they had to work incredibly hard just to move a small distance.

Friction was also important – the teams needed as little possible on the rails. The Subs' rubber wheels were better, even though they gave a lot of rolling resistance compared to the Chariots' steel wheels.

The Subs also looked at the friction of their drive system, reducing it by taking out the pistons from the Land Rover engine. That meant they could turn it over with the rolling road easily – a great help when trying to overcome the inertia of the vehicle and the sand's weight in the haulage round.

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