Buying bus tickets from Santiago to Bayonne with a bike

I found the Alsa website requires that you know if the bus is international, national, or regional. Even then it gets finicky if dates are not yet on the schedule database. Sometimes that means you can't even book two weeks in advance.

I was you I'd try working out how to get from major center to major center ... IE Santiago to Leon, Leon to Burgos, Burgos to San Sebastien, San Sebastien to Bayonne.

I don't know but I have observed bike travellers. Typically the bikes would be folded up in a box and treated as luggage and there is not an issue.

I would also suggest looking at taking the train. The border crossing is a bit complicated because the rail gauges are different but it is doable.

Here are some links. I have not yet had success with finding bus station information for Leon but I think it is operated by Alsa. I have included Biarritz airport as it has some bus connection information for Bayonne:

Estacion de Autobuses Santiago de Compostela
http://www.tussa.org/web/interior.php?txt=arbore_web5&lg=cas

Bus station Logroño
http://wikirioja.com/wiki/Estaci%c3%b3n_de_autobuses_de_Logro%c3%b1o

Estacion de Autobuses Pamplona
http://estaciondeautobusesdepamplona.com/Inicio.aspx

Bilbao Bus Station
http://www.termibus.es/index.php?idi=es

Alsa bus network
http://www.alsa.es/en/buy-and-schedules/international/?searchType=international

Biarritz Airport (BIQ)
http://en.biarritz.aeroport.fr/

Irun train station:
http://en.wikipedia.org/wiki/Irun_railway_station

Hendaye train station:
http://en.wikipedia.org/wiki/Gare_d%27Hendaye

while in santiago, i did heard the bus company will only take a maximum of 2 bikes on board each bus. so if the bus you are going to travel on will not allow you to bring on your bike, try to take another bus. this is based on what i have been told by pilgrims who travelled on bikes on the caminos. these are the pilgrims who stayed in my albergue. you can also arranged for your bike to be sent home. depending on where you live, the cost of preparing, wrapping and transporting your bike starts at 49 euros from santiago.