Bar grip

Bar grip tyres were developed in the 1930s and were the standard military pattern throughout World War II, for vehicles from Jeeps to heavy trucks and armoured cars.

Deliberate shaping of moulded tyre tread design, rather than merely concentrating on a rubber surface that didn't fail rapidly, began at the start of the 1920s.

These followed the same principle of a solid central rib with square-edged blocks, but were developed to improve tread wear.

The side blocks were now isolated from the centre, although linked by another narrow rib, and their leading and trailing edges formed a trapezium rather than a square.

[4] A helical pattern was used to avoid the uneven rolling radius and vibration of a tread with simple crosswise bars and large gaps between.

[4] The stop-rib was only partly successful though; snowy conditions led the Swiss Post Office to use left- and right-handed tyres to balance the force across the vehicle.

As the bar grip gives no escape for this water, they may retain a layer of water-lubricated mud like quicksand that remains extremely slippery.

Bar grips were replaced on light vehicles such as Land Rovers and Jeeps in the 1970s,[7] although they remained on heavy trucks.

This was due to the faster speeds likely for light vehicles and the bar grip's poor tarmac performance.