This article says bike riding requires 1/3 of the energy of walking. http://en.wikipedia.org/wiki/Bicycle_performance. So perhaps a 3 to 1 ratio when comparing bike touring to backpacking for weight reduction? That is, for a 3 pound reduction in rolling weight, an equivalent reduction backpacking weight would be 1 pound. Looking at it another way, you have the ability to carry much more weight on a bike compared to hiking for the same efficiency. Of course, part of your rolling weight is the bike itself, which the backpacker does not need to carry.