Merriwether

Actually, the dynohubs affect performance more than their enthusiasts appreciate. The peformance drain is not a great amount, true, but it is significant. It's enough to make me prefer battery lights, anyway.

How so? It's easiest to see if we just calculate the reductions in speed of dynohubs directly, rather than talking about comparisons to inclines per mile, or feelings of drag. It takes only a moment or two at analyticcycling.com to calculate the effect of various wattage drains on speed.

The Schmidt hub is very efficient, and draws a bit more than five watts of power away to produce three watts of power for the light. Other hubs do less well than that.

Let's suppose, though, that we have a hub that draws five watts of power away from the rotation of the wheel. Suppose a 165 pound (75kg) rider with a decent road bike on fair roads, riding on level ground, putting out 150 watts. Without the generator hub, this rider would travel at 18.63 miles an hour. With a hub draining five watts to produce light, this same rider would travel 18.36 miles an hour.

That's slightly more than a quarter mile per hour speed difference. Or, to put it another way, the cyclist above with the hub would lose about fifty seconds per hour racing against himself without the hub. In Clifton's 208 mile race above, the cyclist with the hub would lose nine and-a-half minutes.

Admittedly, fifty seconds per hour is not a lot of time for a utility cyclist to lose. Nevertheless, suppose you were choosing between two wheel sets neither one of which had a generator hub. Suppose the wheel sets were the same price, but one of the wheel sets caused frictional losses equal to those of the generator hub specified above. Wouldn't you buy the other, lower-friction set? Wouldn't you buy the lower-friction set even if it cost significantly more money?

Another way to consider the issue is to notice that aerodynamic wheelsets that reduce drag by an amount equivalent to the five watt difference noted above are very expensive. And, again, some other generator hubs do less well than draining only five watts away.

Of course, you might say, commmuters don't spend a lot of money on things like aerodynamic wheels. We are willing to forego speed gains for gains in strength and reliability in wheels. So too, one might say, it is with dynohubs. It's a good bargain to trade the speed away for the reliability of generator lights, some of you will say.

All right. Just speaking for myself, though, battery lights are preferable. They don't slow you down to power themselves. They're much brighter, too. Battery lights are less convenient than generator lights, true, but in absolute terms it is not very inconvenient to deal with charging batteries.

In any case, to each his own. If you value the convenience enough for these speed losses, then you do. However, it is worth understanding the speed losses of dynohubs in direct terms, rather than by comparison to inclines or by a subjective feel of drag on the wheel.

All that said, there's a way in which the generators are more in keeping with the idea of the bicycle in the first place. They're a mostly elegant way to use a small amount of human power to do a practical job surprisingly well. The cost in speed, and the larger cost in brightness, move me toward compromising the purity of this vision.