Removing the need to charge batteries on multi-day trips is a strong draw for anyone planning a long point-to-point route. Hub dynamos provide a level of independence that simplifies packing and planning. However, there are always trade-offs when it comes to the added weight of the hub and the potential increase in rolling resistance.
From a practical standpoint, the complexity of the installation is a one-time hurdle, but the failure behavior differs significantly from a simple battery swap. If a dynamo fails in the field, you are often stuck without lights unless you carry a backup.
Does the independence from charging outweigh the added drag and weight for your specific touring style? How do you handle backup lighting when relying on a dynamo system?
For me, the independence from charging is a huge win. If batteries are forgotten, you are just screwed, and on longer rides you have to ration their use or they go dead before the trip is finished. The weight of an extra battery would not be any more than that of two dynamos, but the peace of mind knowing the lights will work regardless of a charger is worth it. As for backup, the concern about lights going out at a stop is minimal if you use flashing LEDs to keep yourself visible like a Christmas tree.
Fair point on the weight, though the real win for me is just removing that one item from the mental checklist. As for the backup, flashing LEDs certainly do the job for visibility, but it depends on whether you are just trying to be seen by cars or actually need to see the road surface on a dark stretch of country lane.
That is exactly why a helmet light is such a great addition. If you have to pick one for backup or extra utility, the helmet light lets you point the beam exactly where you need it to see the road surface or get a driver's attention. For the main lighting, I have found that using a single bulb often isn't enough for those dark lanes, so I have experimented with hooking up multiple generators in parallel to power stronger bulbs and keep the road well lit.
A helmet light is a sensible addition for those bits where you need to pick out a specific detail on the road or signal a driver. It fills that gap perfectly. I am curious about the parallel generators, though. While getting more light on those dark lanes is the goal, it sounds like it might add a fair bit of complexity to the wiring and potentially a bit more drag. It is a trade-off between absolute visibility and keeping the setup simple.
