# The Road Vehicles (Authorisation of Special Types) (General) Order 2003, Paragraph 4

Extent: E+W+S

(1) Any wheel of engineering plant which is not fitted with a pneumatic tyre of soft or elastic material must be fitted with a smooth tyre and have the edges rounded to a radius of not less than 12 millimetres and not more than 25 millimetres.
(2) But, in the case of plant which is a gritting machine designed for use (and used) for gritting frosted and icebound roads, any tyre of the gritting machine may be fitted with diagonal cross bars which—
(a) are of equal width (which must not be less than 25 millimetres);
(b) extend the full breadth of the tyre; and
(c) are arranged so that the distance between the adjacent cross bars is not greater than the width of the crossbars.
(3) A tyre is not to be taken to be of soft or elastic material unless the material—
(a) is continuous around the circumference of the wheel, or fitted in sections so that, as far as is reasonably practicable, no space is left between the ends of each section;
(b) is of a thickness and design that, as far as is reasonably practicable, minimises vibration when the vehicle is in motion; and
(c) is free from any defect which might in any way cause damage to the surface of a road.

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Source: https://www.legislation.gov.uk/uksi/2003/1998/schedule/3/paragraph/4 (the official version)
Page: https://openlegislation.uk/road-vehicles-authorisation-of-special-types-general-order-2003/schedule-3/paragraph-4
Contains public sector information licensed under the Open Government Licence v3.0. Source: legislation.gov.uk, The National Archives.