OK so this is the 3rd time I have written this - I hope it works.
About the R1, absolutely it is no good for bikes with thin tyres. If your road bike has medium tyres then it is OK is terms of physically coping with the R1 trail (and it is a trail) but distance-wise the R1 is a nightmare. It was formed with the intention of being only scenic and not distance motivated. See my homemade diagram attached to illustrate with I mean.
The path contains many seciton of gravel track nad mud track. Most of it is tarmac but not all, perhaps about two thirds. I assume you are getting the boat to Hook of Holland. Cycling through Holland is easy - just use the street signs that have RED TEXT ON A WHITE BACKROUND. These are for cyclists. IGNORE ANY OTHER COLOURS (e.g. green text) as these denote other R1 style scenic routes and will take much longer to complete. Just plan from town to town to get to where you need to go: so look at the major towns on the way to your destination and go from town to town using these sign posts.As for Germany, it is confusing because Germany also has these sign posts with red text ona white background but these are much less efficient and are scenic only. You should plan using B-style roads. Buying MARCO POLO maps is your best bet as all the safer B style roads are clearly marks as YELLOW ROADS (don't follow the bicycle routes on the map - again, these are just scenic and not efficient). These are by far the best way to travel through Germnay - most of them are scenic, providing a nice mixture of nature areas and cities, not too busy, have many cycle paths by the road and are very direct, in fact, much more direct than highways as these tend to meander a lot. It should be knwon that you can cycle on any roads in Germany apart from the Autobahms unless it is clealry sign posted that cycles are not allowed (same types of red circular signs as in the UK). If there is a cycle path however, you are obligued to use that rather than the road, and the cycle paths vary MASSIVELY from smooth tarmac to nasty cobble-stone. Good luck.
