Re: Commuter lights

Mike Sales wrote: 
"D.M. Procida"  wrote in message

Also, I guess that dynamos have changed since 1982, because the ones I
used around then, which pressed on the tyre making a racket, would slow
down a bike nearly as effectively as a brake. And it seems a shame to
expend my puny output for lighting when I can need it all for the road.



Interesting data on the drag of vaious dynamos at
http://www.myra-simon.com/bike/dynotest.html.


"Everyone (who doesn't use one) complains that dynamos slow you down. Well
okay, of course they do, but I suggest that the slowing down has more to do
with psychology than the actual power required to turn it. It takes energy
to make a noise, your energy. Add the lowering tone (eee becomes urrr) as
speed drops on a hill and it becomes hard not to believe this morale sapping
device is responsible blame for the pain in your legs and the sweat on your
brow! "

"All of the generators were easier to turn than riding up a 1 in 300 slope.
Another way of putting that is a rise of 18 feet per mile; and there's quite
a cluster of sidewall and hub-driven models around the 1/500 line, or 10 ft
per mile. If that's a hill I'm a Dutchman! Let's put this into another
context. Our 90kg (total) cyclist must produce about 70W to maintain 20 km/h
on the flat. If he turns on his dynamo he needs another 6W minimum, 14W
maximum. He can work a bit harder or slow to 19 km/h, 18 minimum. Now that's
not too bad is it?"

I also calculated that at an average output of 150W, the 6W drag of a SON would get me from London Fields to Dunwich 7 minutes slower.
.

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