Lifted the following from
http://visitbath.co.uk/travel-and-maps/parking-in-bath
Motorcycle Parking
Please note that parking is only free in designated motorcycle parking bays in the following car parks:
Charlotte Street (next to the disabled parking bays at the main entrance)
Avon Street (Avon Street, on the lower level of the multi storey car park)
Broad Street (Broad Street, adjacent to the pay and display machine)
Bath Sports & Leisure Centre (on the paved area under the walkway and also in the undercover area on the left hand side)
Motorcycles not parked in these bays (i.e. parked in normal car parking bays) will be required to purchase a ticket the same as other motor vehicles.
In addition to parking bays, there are secure points at the following locations:
Portland Place
Sydenham Buildings
Westgate Buildings
Hope that helps.
Dennis