I hope to cycle from Cherbourg down the French coast to Irun and then join the
Camino Frances , any advice would be much appreciated. Starting in September, nd 70 years old
That'll be a great adventure! I don't know how much cycletouring you've done, but happy to answer any questions you may have, either on this forum or by direct message.
You might want to join the UK pilgrim association (Confraternity of St James), who have lots of advice in their website and can put you in direct touch with others who've undertaken similar journeys recently.
Whether you have a roadbike or a hybrid, you should have tyres with good puncture protection and durability. If you prefer to be out of the traffic, the Velodyssey route down the French coast is well signposted and usually reasonably surfaced, though it often skirts around the interesting villages and places to see, restaurants etc. Or there are several tradirional pilgrim routes, not specifically for cyclists, which you can more or less follow on minor roads. Might also be worth a look at the Veloroute Francette, which follows a mixture of minor roads and former railway lines from the North Coast to La Rochelle. The accommodation options are more expensive than in Spain, though camping is an option.
Once on the
Camino Frances, there are decisions to be made about following the roads or the hiking path. September will still be busy, with hundreds of pilgrims on every stage (including me, on foot this time!). As discussed earlier on this thread, if sharing the path, there is an obligation to go slowly, carefully and considerately.
Cicerone has a recently updated guide (which starts in Le Puy, but follows a mainly on road version of the Frances). If you can manage a bit of French or German, the Rother guides have very good maps and their routes manage to combine the most suitable parts of the path with low-traffic roads.
There is lots of talk of albergues prioritising walkers over cyclists, but in most instances there isn't an issue, where a cyclist isn't welcome, anorher option is always available.
I hope some of this is helpful, but do follow up with any specific questions; there's lots of expertise on this forum!
Good luck and buen camino!