Wow wide topic.........but I'll have a stab.
Lets look at the words from the Oxford series -
ADVENTURE
1 [countable]
an unusual, exciting or dangerous experience, journey or series of events
her adventures travelling in Africa
When you're a child, life is one big adventure.
adventure stories
Popper described science as the greatest adventure in the world.
2 [uncountable]
excitement and the willingness to take risks, try new ideas, etc
a sense/spirit of adventure
I set out across the country looking for adventure.
RIDER
1
a person who rides a horse, bicycle or motorcycle
Three riders (= people riding horses) were approaching.
horses and their riders
She's an experienced rider.
a motorcycle dispatch rider
2 rider (to something)
an extra piece of information that is added to an official document
So in our context of Adventure Bike Rider -
We are looking people that ride a motorbike in the broadest terms with a spirit of adventure. A willingness to try new things and to push yourself outside of the normal comfort zone.
This works on many levels and is dependant on the rider in my view.
Me riding to Paris is not an adventure - I have done it many time before and know the roads, customs and pit falls.
Someone that has only just passed their test or never gone further than the local bike hang out then this would be an adventure - making them an Adventure Bike Rider.
The same would apply to someone that has not done Fell Riding before - to head up over the passes in Cumbria and Scotland would be as equal to an adventure as heading off to the Alps for that person. As a person that lives near the Alps would not see it as much of an adventure and just a nice day out.
In this shaded area of who is an Adventure Rider we could take it that we all are.
For me there are levels to this comfort zone pushing and someone setting off around the world would be seen in many peoples eyes as an adventure.
But all adventures are yours to make - it is just a matter of how extreme you want to make it for yourself.....and of course your budget
An American riding acoss Venezuela would find this an adventure but a Venezuelan would see this as 'just getting to the shops to sell thier corn' and nothing more than a ball ache of a ride.
This is yet another reason that ABR Magazine is so cool! It recognises this fact and will publish articles from a ride to Romania to see a Vampires Castle to Riding the Pan American Highway and everything inbetween along the way.
So for me - Beauty and Adventure are in the eye of the beholder
Cheers
James