Great idea's girls!
The Bike Challenge and the Walk Challenge would have to be two seperate challenges otherwise you would need a 12 to 1 ratio because of how much easier it would be to ride 1 kilometre compared to walking it.
You can put up your challenges on the challenge thread if you like and see how many take up the challenge.
Perhaps see who the first person to get to 20 kilometres is with the Walking Challenge (be it walking on the street or on the treadmill)
And the first person to get to 50 kilometres on the Bike Challenge.
To the Challenge Thread - http://www.weightloss.com.au/forum/viewforum.php?f=19