drew
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response 2 of 7:
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Aug 21 19:38 UTC 2008 |
I want to experiment with higher gear ratios that are commonly available on
bicycles. I plan to run one chain from the largest pedal sprocket to the small
sprocket on the spare spool, and a second chain from the large sprocket on
the spare spool to the aft gears. I figure that the new 1st gear (out of six
to be used) should be the same as the current 18th gear (3 front and 6 aft),
which I'm now using exclusively as I've found I get the best overall speed
to effort ratio just by leaving it that way and standing on the pedals.
I have reason to believe that I might be able to get more speed with a higher
gear ratio (though I'm not yet certain of it), mitigating a major disadvantage
of bicycles versus powered vehicles.
The chain I can get at WalMart if I absolutely have to. The spool is a bit
more difficult to find short of taking apart a perfectly good bike. I'm hoping
for one from a bike that is sufficiently trashed that the spool won't be
missed.
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drew
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response 4 of 7:
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Sep 29 03:47 UTC 2008 |
We've figured out a means of mounting the gear spool to the bike
frame such that it should turn easily enough, but have run into an
unexpected problem. It seems that part of the bike frame, specifically
that part which runs between the two existing gear spools on the chain
side of the bike, is in the way of all possible routings for the chain
between the new gearspool and the presently existing one.
<PRE>
[]
##=======. ===_
(XXXXXXXXXXXXXX) }=(__)
\/___====' ^ ===
B.^ A. []
A. Secondary spool is to mount approximately here.
B. This part of the frame would be in the way of the chain.
=====
\
/ \
_.----._ ' \
.' /`. \--------A.
/ / \ \ =/=
| / | \ /
| ()============( )
| B.^ | /
\ / =/=
`._ _.'
`----'
</PRE>
We've determined that it would be possible to run the chain without
interference from the frame if we could run the bottom of it directly
from the bottom of the gear spool instead of through the deraileur.
However, with the current gears I'd have to pick a single overall gear
ratio and be stuck with it; and I will still need the gear ratio that
I'm using now (current maximum gear) to start out in. So the path of
least resistance seems to be to get hold of an internal gear hub, that
I may run the chain directly, get rid of the deraileur entirely, and
still have multiple gear ratios. This would have an additional advantage
of more solid contact between the chain and the aft gear, and possibly a
coaster brake if I'm lucky.
Therefore I'm now looking for a 3-speed internal hub, by strong
preference attached to a 26 inch mountain bike wheel. (The tire and tube
should not be necessary so long as my current tire and tube fit it.)
From what I've found out it seems that most of these have 22 teeth on
the sprocket, and internal ratios of 4/3, 1, and 3/4, giving equivalent
gears of 29.333, 22, and 16.5 teeth, slightly slower than the 28 through
14 teeth that I would have gotten with a deraileur-shifted spool; and
I would have two fewer intermediate gear ratios than planned. But I can
live with that. (A 5 speed internal hub would be better, but those are
rather rare.)
(The smallest sprocket in the forward chainring spool can be removed;
and I had thought of somehow either making it freewheel or getting it
out of the way so that we can route the bottom of thechain in the same
direction that it currently goes, directing it to the secondary spool
with a pulley. But we don't have a good way of making this happen.)
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keesan
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response 5 of 7:
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Sep 29 14:02 UTC 2008 |
Jim has purchased two 5-speed internal hubs which he plans to use some day,
non-coaster-brake. He gave the last 3-speed with coaster brake to a friend.
There are lots of used 3-speed bikes with internal hubs around, probably $10
at Kiwanis rummage sale. 26" non-mountain (thinner) rims. fractional instead
of decimal tire size. 1 3/4 (inches?) instead of 1.75. You could rebuild
a mountain bike wheel with one of these hubs. Most do not have coaster
brakes. Ask for an old 3-speed bike on your local craigslist or ecycle.
Bike Nashbar might still sell 5-speed internal hubs.
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