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Since,

Pressure = $\frac{\mathrm{Force}}{\mathrm{Area}}$

The double tyres increase area of cross-section without increasing friction, and hence decrease pressure on the axle.

Answer

Since,

Pressure = $\frac{\mathrm{Force}}{\mathrm{Area}}$

The double tyres increase area of cross-section without increasing friction, and hence decrease pressure on the axle.