Arches np and canyonlands np are by reservation only and you must reserve online. There are a number of first come first serve campsights along hwy 128 on the Colorado river ( just east of the park) which IMHO would be a better bet for bike camping. More fun too without the pestky np rangers noseing around all the time. There are 2 fabulous campgounds just south of Moab on Kane Creek road, again right on the Colorado river in this gorgous red rock canyon. My wife and I just returned from spending a week camped there. It is only a few miles from town so resupply is a breeze but seems like miles from nowhere.