Ryan Cousineau said:
Reid Priedhorsky said:I shift my 3-ring chainwheels with a Tiagra brifter and a Sora
derailleur. This works great, except that it is very difficult (i.e.,
pretty much impossible) to adjust the shifting so that I can use both
the middle chainwheel with the smallest cog and the largest chainwheel
with the largest cog (or even the largest two). I have 9 speeds in the
back.
(As an aside, I know that you're not supposed to use the large
chainwheel and the large cog together, because it increases wear, but I
find that combination very useful, so I'm willing to put up with extra
wear.)
Aside from a longer wheelbase, nothing is ever going to make your
gearing choice pretty. At the risk of coming off hostile to your
informative and friendly request for help, why in the name of all that
is good and holy aren't you in your middle ring in these situations?!? I
guarantee that you've got a gear somewhere around middle-middle that
will reproduce whatever gearing you hope to get from either small-big or
big-small (indeed, these three ratios will all end up being fairly
close).
Hi Ryan,
It's a legitimate question, and I do have plenty of duplication. The
reason is that starting out in the big-big combination makes it easier to
access the smaller cogs which are the "sweet spot" in level cruising. If I
don't anticipate using these soon, I do shift down to the middle ring.
To elaborate, here's my setup. Numbers in the table are gear inches.
52 42 30
---- ---- ----
34 41.3 33.4 23.8
30 46.8 37.8 27.0
27 52.0 42.0 30.0
24 58.5 47.3 33.8
21 66.9 54.0 38.6
19 73.9 59.7 42.6
17 82.6 66.7 47.6
15 93.6 75.6 54.0
14 100.3 81.0 57.9
Now, if I'm going to be moving quickly, I usually end up on the large
chainring in the neighborhood of 19-15 teeth in the back, perhaps 14. The
smallest cog with a duplicate on the middle chainring is (roughly) 17.
Shifting the rear cogs is considerably faster and can be done under much
greater load than shifting the chainrings.
For example, if as I speed up I want to end up in 52x15, I can either
start on the middle chainring (on, say, the 27) and do 7 fast shifts and 1
slow one (to 24, 21, 19, 17, 15, 14, large, 15) -- not to mention that
during my stopping, I would have had to to throw down several rear gears
_and_ shift the front -- or I can start on the large chainring and do 7
fast shifts.
From a usability standpoint, the latter is clearly better.
That's why I want my "deranged" shifting pattern. My ideal (which I don't
do fully because the front derailer grinds on the chain) is to use the
large chainring when I'm in places where I go fast, medium for medium to
slow places, and small for very slow places.
Quoted message said:I'm not going to
tell you that [...] your nearest relative to start speaking only in
palindromes,
Bummer. I'd ride around in the small-small to see that.
Quoted message said:This sort of crossed-up gearing choice is the prime circumstance for fun
failures like breaking a chain, or maybe even a rear derailer.
I think I need some actual evidence that these are real risks before
believing that sentence. I just don't see how a dozen millimeters of
deflection is going to trash my derailer.
Take care,
Reid
