Q I have been told that to operate a vehicle running
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empty, fitted with a trailing rear axle and an air transfer device, with the trailing axle raised so that the wheels are just off the ground is against the law. Is this correct?
A There is nothing specific in the Construe' tion and Use Regulations which would prevent a vehicle being so operated. But this practice is often not possible unless the vehicle was designed in a particular way, because of the change in wheelbase and overhang which can result in the latter being in excess of the legal allowance.
Now that the overhang can be 60 per cent of the wheelbase, the position is a little easier and on many vehicles raising the rearmost axle is quite possible. It is best to consider a specific example which in this case will be a six-wheeler with an 18 ft. wheelbase when from the front axle centre line to the centre point of the rear bogie the overhang can be 11 ft. 1.5 in, This is made up of 60 per cent of 18 ft. plus 4 in. because on multi-wheel vehicles overhang is treasured according to the regulations from a point 4 in. to the rear of the rear bogie centre line.
In this particular example, if you raise the rearmost axle you would reduce the wheelbase to 16 ft. and there would be an illegal overhang. But if the vehicle had a dimension of 9 ft. 7.2 in. from the centre line of forward rear axle and the end of the frame (that is 60 per cent of 16 ft.) this would be in order. So if the overhang from the centre line of the bogie was 7 ft. 7.2 in., with the bogie axle spacing 4 ft., the rearmost axle could be raised without contravening the law. This is quite practicable particularly on tipping vehicles.