ACU (for interest nowadays)
EXHAUST pIpES1. The end of the exhaust pipe or pipes must not project beyond any part of the vehicle or its bodywork. Exhaust gases must not be discharged so as to raise dust or foul the tyres or brakes, or inconvenience a following rider. The end of the exhaust pipe for a minimum distance of 30mm must be horizontal and parallel (within a + or −10 degree tolerance) to the fore and aft
EXHAUST pIpES1. The end of the exhaust pipe or pipes must not project beyond any part of the vehicle or its bodywork. Exhaust gases must not be discharged so as to raise dust or foul the tyres or brakes, or inconvenience a following rider. The end of the exhaust pipe for a minimum distance of 30mm must be horizontal and parallel (within a + or −10 degree tolerance) to the fore and aft