Originally Posted by
ilchymis
I plan to keep a dynamo of some sort on this bike, in any case. So for me, it's not a choice between a dynamo and no dynamo. Rather, it's a choice between my current Shimano dynamo and a potentially more efficient SON dynamo.
If my memory is correct, the biggest efficiency difference between the SON and Shimano hubs comes when the lights are off. In the on position, I think the gain is quite small at a large $ cost. I leave my lights on all the time as I figure the efficiency savings between on and off won’t be noticeable to me, the switch is probably the weak link in the system so don’t mess with it; and, while I’m not really a believer in safety benefits of lights in daylight, why not? There are probably other reasons one might choose SON over Shimano but, if one leaves the lights on all the time, a gain in speed would be at the bottom of the list of reasons for me, not the top.