I am going to be pilgramaging to compostela this spring but had always had it in mind to do it on a bicycle as my girlfriends grandfather did it, he started in Paris, but I feel I would enjoy the Arles route more, has anyone done it on a mountain bike before, any comments would be wonderful, thank you for all the great insight already.
If you plan to follow the paths destined for walkers, you will need a mountain-bike of good quality, at least for some parts of the way. (I am a walker, therefore I cannot give you more advice about bicycles.) But it is also possible to follow roads near the paths. In the french topographical maps of 1:100'000 you will not only find the roads, but also the paths (indicated GR 653).
did you do the trip? if so can you give any good advice for another cyclist like me?
I am also interested in doing the route from Arles by bike. Has anyone done it and can give me some advice, please. Also I would like to cross the mountains at SJPP, and then walk the remaining distance to Santiago. I presume it is possible to change the route? I intend to leave Arles at the end of August, and leave SJPP mid September.
The place where the GR653 Arles route is the closest to the GR 65 Le Puy route (where SJPP stands) is Oloron-Sainte-Marie. There's a trail that goes along the Pyrenees (GR78), east to west, and that connects both Oloron and SJPP. There's a description in French of the Piémont route here. Look at stages 20 to 22, approximately 60 km long.
Also visit the IGN web site(National Geographic Institute), type "Oloron" in the research field ("rechercher un lieu ...") and zoom to 1: 60000 to 75000 scale so you can see the GR78 drawn on the map.
Can't give you any advice since I walked the Arles route. I just remember parts that might be difficult for biker : between Saint-Guilhem-du-Désert and Arboras and between Le-Bousquet-d'Orb and Saint-Gervais-sur-Mare. For these sections you may have to push your bike during kms or otherwise take alternate small roads.