Question to the Department for Transport:

To ask Her Majesty's Government how any post-manufacture alteration to a motor cycle exhaust system is monitored to ensure that any changes conform with legislation.

New motorcycles are required to meet strict noise limits in a range of driving conditions before being placed on the market. The current limit within the approval test is between 73 and 77 decibels (dBA) depending on the power to weight ratio of the machine and is not specific to types of roads.

Once on the road, regulations require that exhausts and silencers shall not be altered to increase noise above the level the motorcycle was originally approved to. The police also have powers to take action if they believe excessive vehicle noise could have been avoided through reasonable driver care.

The annual vehicle MOT test requires an inspection of the state of repair of the exhaust and the tester uses their experience to make a subjective assessment of the noise levels. A vehicle should fail the MOT if the silencer has been altered to increase noise above the level expected from a standard system.