coast 2 coast wrote:Dynamo hubs add extra weight and extra rolling resistance, two concepts generally considered to be undesirable on a bike. They also add extra complexity and extra expense...
Weight? -Not much. A good system is about 0.5% of the all-up weight and a bad one is 1%.
Rolling resistance? -No; rolling resistance varies with load carried, dynamo drag doesn't. With the lights on a decent generator drags about 5-6W. By contrast IIRC each (touring) tyre drags several tens of W at ~20mph and aero drag is much, much more again. People invariably don't even notice if the lights are on or off. With the lights off, the drag is less than 1W with a good generator. I reckon my present generator drags less than 0.5W, lights off.
Complexity? -Surely this is only a problem if it adds unreliability? For example freewheels / freehub bodies are 'complex' and most people don't choose to service them because they are pretty reliable and can be replaced more easily than overhauled in the event of trouble. I have never heard of the electrical parts of a generator failing in normal service, and if you want to be able to service the bearings (in an entirely normal way, just a little more difficulty on the RHS) then get a shimano generator with copper windings in it (some have aluminium windings). In the worst case with a shimano generator you might have to unscrew the innards and replace them, just like a freewheel....
Expense? -Really? How do you value your time? How much do you spend -in time and cash- on batteries, battery lights, and faffing about with them?
I have used a hub generator for over 30 years and have ridden tens of thousands of road miles on it. In the meantime I have used battery lights for other bikes, offroading etc and I have spend ten times as much money, and a hundred times more time on the battery lights for one tenth or less of the riding time. I have also suffered innumerable failures in the battery lights, none in generator systems in this time; not an unusual experience... If you are doing a reasonable mileage in the dark, for reliably seeing where you are going on the road a generator system is a vastly superior arrangement.