Two persons on a motorcycle can travel at 25 times the speed they can manage on foot, given an open road. Yet unless they tow a trailer, they are likely to have much less carrying space than they would with backpacks. This calls for discipline in packing bulky articles, evidently including books.
The relatives who have just come through either developed or learned a system by which two persons can share one book: the leader reads along to a convenient breaking point, and tears off the portion just read, to be handed to the follower. They are reluctant to treat a good book this way, and so have been serially sharing Dan Brown's novel Lost Symbol. It was looking pretty well plucked this week, after 5000 miles and about 20 days of such treatment.
I have respect for books as objects, yet I don't know that I'd subject myself to Dan Brown to show it. Perhaps for the sake of the motorcyclists we should revert to the old custom of publishing novels in three volumes. Or American publishers could learn to publish slimmer volumes, as the British and the French (at least) know how to.