We have recently walked the Aragon Route of the Way of St James: Somport Pass - Jaca - Sangüesa - Puente la Reina. I had been asked by a friend for information on the possibilities of following the trail on a mountain bike, so we kept our eyes open.
The Aragon arm of the Camino is not the main route. It is much quieter. We saw ten other pilgrims/walkers and four cyclists in the ten days we were walking the Aragon Route. We joined the main trail for a few km on our last day. We saw about 40 pilgrims and 2 cyclists in the hour we walked down into Puenta la Reina. I suspect the Aragon Route is a lot wilder and more mountainous than the main trail. There is little information about cycling available from Tourist Offices. I enquired whenever I had chance.
The “Camino de Santiago en bicicleta” is a club dedicated to cycling the Camino. Most of its info is in Spanish, including maps. People do cycle the route. There is a guide in Spanish available from the “Camino de Santiago en bicicleta”. The Kompass 1:100 000 walkers’ map struck us as being useless for cyclists from what we could see.