Bicycle: Mainz to Boppard or Mainz to Speyer?

For a four day bicycle tour starting in Mainz, which way would you recommend — north to Boppard (hitting the various castles, Bacharach, and St. Goar) or south to Speyer (hitting Bodenheim, Oppenheim, and Worms)?

Background: My son and I will be in Mainz about four weeks from now, and we're trying to decide which way we should do our brief bicycle tour along the Rhine. We'll pick up our bikes and drop off our luggage in Mainz, and then spend four days riding to either Boppard or Speyer, and on then we'll take the train back to Mainz to return the bikes. Neither of us have been along the Rhine valley before, and I want this to be a very leisurely ride with plenty of time to sight-see and take pictures. So which way do you recommend?

Hallo woief,

Scenery wise I should recommend the Middle Rhine leg to Boppard. But pretty crowded on the cycle-paths. Unesco World Heritage area. If you don't mind some climbing 'sidesteps', some great panoramas, for example near Bacharach and Oberwesel
The Mainz - Bingen part through Ingelheim crosses interesting orchards, esp plums and is very quiet. But most cyclists prefer the opposite bank through Eltville (can't review that personnally)

More relaxed cycling to the south, partly on small roads among the vineyards; the southern part, Worms - Speyer less interesting qua landscape. But historical (Worms/Speyer) and museum wise ( such as Speyer, Technik Museum ) some gems.

Well, then to Boppard it is — thanks for the help!

Any other specific suggestions for what to stop at between Boppard and Mainz? (I've already noted Bacharach and Oberwesel). There are just so many supposed must-sees, so I'm wondering what must we actually see.

Again, thank you!

As for the towns, you can hardly go wrong. St. Goar, Ingelheim and Bingen, all interesting from various points of view.

Consider to cycle to Koblenz, there´s much to see/do and IMO Boppard can´t really concur with the other sites/sights.

And the castles of course. Too much to list, I liked Stolzenfels and note some consensus on this Forum about Marksburg as a must, the only castle on this part of the Rhine never having been destroyed.

South of Mainz (in fact also downriver between Mainz and Bingen) the Rhine valley is rather wide an flat. Thr river is channelized and flows between dykes. It can be 10 or even more km on either side until the hills begin. Though Speyer is a gem, I do recommend to follow the Rhine downriver. For most of the route there is a separate cycle path parallel to the trunk road. The landscape is brilliant, there are castles, there are ruins, there is the river, there are trains on both sides.

Four days allow plenty of time and you will not have to hurry. You can change sides at several ferries, catch a train to repeat parts of the route.

When you cycle from Mainz to Koblenz via Bingen, you first come through some industrial parts of Mainz, but the scenery improves very much after a few km. In the Middle Rhine valley, the best part is from Bingen to Bacharach, where you can cycle along the river.

From Bacharach to Spay, you would have to use the bicycle lane along the highway or head into the hills. The last part from Spay to Koblenz is right on the river again.