Motorcycle Licencing Information ...
There's a fair amount of uncertainty in Western Australia about what are the registration options for trail bikes.  We put together this information page to provide an overview of the current situation.  Please note that this information is subject to change and should not be relied upon without checking with the relevant authorities.
A Class Registration (full road registration)
This level of registration is available to ADR compliant motorcycles and provides unrestricted access to the public roads network.  It also includes third-party personal insurance to protect rider against any claims made for personal injury in the event of an accident for which that rider was responsible.  Only motorcycles that have a Compliance Plate signifying that the vehicle complies with all requirements for registration are eligible for this level of registration.  This means mirrors, indicators, speedo, lights, mudguard extenders etc.  It is not possible to simply fit these items to a motorcycle that does not already have a compliance plate in order to register it.
B Class Registration
B Class registration is a conditional form of registration that is available for motorcycles and ATVs that do not have a compliance plate but to which have been fitted head and tail lights, a working stop light and a muffler that limits noise level to no more than 94 dbA.  Mirrors, batteries and a horn are not required and choice of tyre is free.  This is a restricted level of registration and B Class motorcycles and quads can only be used on a public road whilst participating in an event arranged by Motorcycling WA or other organisation approved by the DPI.  Third-party personal insurance cover is provided by the State Government Insurance Commission while the motorcycles or quads are being used in competition. Because of this limited insurance cover B Class Registration costs significantly less than A Class registration . 
Off Road Vehicle (ORV) Registration
In order to access the designated off road vehicle areas - Lancelin, Gnangara and Pinjar - motorcycles, quads and other off-road vehicles are required to have ORV registration. They can be registered at any licensing centre.  The fee is currently six dollars with a one-off six dollar fee for numberplates the first time the vehicle is registered.  All off road vehicle registrations expire on 30th of September each year.  ORV registration does not include any third-party insurance.
So what does it all mean?
If you own a fully registered, ADR compliant bike you have access to all the same public roads and tracks throughout Western Australia that any other registered vehicle such as a car or four-wheel-drive would have access to.
If you own a motocross bike or other non-ADR compliant vehicle, or if you own a registerable trail bike but choose not to fully road register it (for example because you have no intention of riding it on the road) then you can register it as a B Class vehicle and use it on the road during Enduro competitions (these include non-competitive events such as the Adventure Rally and Capel 200).
If you intend to ride your bike on public land anywhere and it doesn't conform to either A Class or B Class registration then it should be registered as an off-road vehicle and only used in the designated ORV areas.
Some Useful Links
Off Road Vehicles Act  Department of Planning and Infrastructure
The above information is courtesy of the RTRA
DPI Vehicle Examiners Instructions for B Class Registration.
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