On Sun, 22 Apr 2007 13:17:12 -0700, "Bill Sornson" <
[email protected]>
wrote:
>Michael Hearn wrote:
>> My wife and I have a Cannondale tandem. The front shifter shifts to a
>> larger ring by tensioning the cable. A spring shifts it to a smaller
>> ring (slack cable.) Are there derailers out there that do the
>> opposite... shift to a smaller ring by tension. If we have any
>> tension on the pedals at all, (like starting a hill) It won't shift
>> to the small ring. Yea, I know, shift sooner, but dropping to the
>> granny while on the flats keeps us from getting any speed up for the
>> hill. surely we are not the only ones with this problem.
>
>Common mtb issue. Try the "thumb adjustment": push in on the FD cage with
>your thumbs...firmly. Usually works.
>
>If all else fails, get out some directions and adjust your cable tension
>and/or limt screws and/or FD position.
>
>Also, even if climbing you should be able to ease off the pedal pressure
>just for a second or two to help the shift.
>
>All is not lost... BS (no, really)
Yes, yes and yes!
1. Inner limit screw too tight.. or shifter hitting the frame
prematurely.
2. Cable not slack or binding on release. .. should be slack at this
point.
3. Cage not square to rings.
4. Technique:
Shift at or above 70 -80 RPM before you are already getting into
trouble.. Practice doing this under light load until you find
out just how much pressure you have to relax to make it
work.
Split this shift with the rear by going up a couple on the back at the
same time so that you don't lose your momentum JUST BEFORE you get to
the bottom of the hill. This will solve your issue of losing speed
and momentum before you have to.
(Most stock triples with almost any rear cogset will give you about
one gear ratio change if you shift the front one way and the rear a
coupleof clicks the other).
Check Sheldon's charts to see this on paper.
If you can learn do this, then you'll have a bunch of cogs to drop in
the back one or two at a time as you need them on the hill.
ie: don't wait until you are all the way in on your cassette before
you shift to your "granny" on the front.
(Mountain biking can put you in this situation almost before you can
say. "ooops"!!) On the road, you should be able to preempt this
problem almost completely.
If you do this shift to the 'granny" on many bikes at low crank speed
or heavy load, there is always a chance for some kind of problem,
such as "chain suck" or dropping between the rings, or not completing
the shift etc. etc. so do it early and keep your road speed up by
grabbing a couple on the rear at the same time.
I used to drive trucks with "Triplex" transmissions or "Two speed"
rear axles, both of which require some shifts to be done
simultaneously to get to the "next" ratio in the sequence, so it came
naturally to do this on my bikes.. Not much of a mystery so try it.
In the "Triplex" system, every third shift, you had to do with no
hands on the steering wheel by reaching through the spokes to get at
the main lever while shifting the triplex simultaneously!!! Some fancy
clutch work was also in order to not let everybody around you know
what you were doing or thought you knew how to do <BG>
With STI stuff on a bike, you will release both "little" levers at the
same time to drop one gear on the front and pick one up on the rear.
Or conversely, pushing both of the longer levers at the same time
would go up on one the front and down one on the rear, keeping your
cadence and road speed close enough to what it was before the shift
but positioning the chain into a much more desirable spot on the
cassette for the continuation of the hill or decent.. whichever. .
Most of these derailers have such a mother strong spring
that it will knock the chain onto the small ring
(or even onto the bottom bracket) if released
far enough. <G>
Try the inner limit adjustment 1/8 turn out at
a time on the stand until you can see the mechanics of what
is happening. After you get it to shift (and not overshift), work on
technique..
Let us know how you make out...
Never rode a tandem but sure would love to give it a shot.. !!
Bob F.
