Pooh said:
I have the following setup: 26" Specialized Rockhopper an older double butted chro-mo handmade
frame that I like and use as a utility bike. My riding area is hilly, with fairly steep hills.
My gearing is 21 speeds with a Bontrager 4-arm 104 mm BCD triple
44/32/22 tooth gears And a hyperglide 7 speed cassette rear from Harris Cyclery with
34/29/24/20/17/15/13 tooth gears.
The 12-14-17-20-24-29-34 is better spaced for the half-step -- I think this is custom, but
do-able. I rode something close to this across the US on a loaded tour in the early '90s. Then, I
think I used:
26 42 46 12 58.500 94.500 103.500 14 50.143 81.000 88.714 17 41.294 66.706 73.059 20 35.100
56.700 62.100 24 29.250 47.250 51.750 28 25.071 40.500 44.357 32 21.938 35.438 38.813
At that particular time the 34t rear had not been "reintroduced," the 29t didn't seem to exist, and
the Shimano and SunTour r-ders didn't have the wrap-up capacity of max cog capacity of the
components today. I'm currently running a 48-44 w/ a 11-12-14-17-20-24-29-34 (no granny) for
experimentation and I do like it very much -- it is quite practical as far as the riding experience
goes. The 11t is just an extra cog, not part of the half-step. I don't really cross the 48x34
either. I use the "short cage" XTR derailleur for which Sheldon says he "doesn't sell the silly
things" (and I do understand why).
Quoted message said:Using the Effective Cycling logarithmic gear chart in chapter 5, I laid out my setup and came up
with a half step if I replace my 32 tooth chainwheel with a 41 optimal, or 42 tooth chain ring. I
believe this result is correct.
Probably, it sounds about right.
Quoted message said:My problem: I can't seem to find a 41 or 42 tooth gear to install in the middle gear position.
As others have pointed out, the 110/74 crank is the best for selection of rings.
Quoted message said:The gears I did find have the bolt counter bore on the pedal side of the gear meaning that it is
for the third chainwheel position.
This is a persistant problem today when trying to run closely sized chainrings. Some custom work is
likely to be called for if you really want to push forward on this.
Quoted message said:Of course, if I reverse the gear then the machined ramps for the granny gear are lost.
Well for a half-step, you don't need ramps/pins/gates for the middle-big changes. The step is so
small the front shifting is _very_ crisp. The bigger problem for middle-big changes is that the
rings cannot typically be placed close enough together. I still mess with half-steps and have two
set-ups today. If the middle and big rings are not close, then the chain can tend to not shift down
onto the middle rings so well and may "ride" along the teeth of the middle ring. Consider that the
step size of the chainrings for a half-step are on the order of that for 1t step racing clusters:
the rings should ideally be just as close as cogs are, but you'll have difficulting making this so
because no manufacturers intentionally support the half-step paradigm today.
The shift from granny to middle might seem bad, but in practice it goes pretty well.
You haven't mentioned the need for the front derailleur. The half-step front is a special beast and
again no manufacturers intentionally support the half-step paradigm today. If you really do decide
to pursue the half-step, just ask again and I can help with some front derailleur advice.
Quoted message said:I also tried this on my Shimano LX 4-arm 104 mm BCD and found that the chainwheel is not
reversable from the outside to middle position (meaning that it does not fit and there is
interference).
Again, consider a 110-74 crank if you really want a half-step plus granny. It looks like Nashbar
just sold out of their sub-$30 "CPI" 110-74 touring crankset.
Quoted message said:1. Do I still want to continue on this line of reasoning?
Only if you are willing to do plenty of messing around.
Quoted message said:2. Is half step gearing a reasonable thing still
Yes, from the perspective of actually using it. Half-steps are second best to crossovers in ease
of shifting.
Quoted message said:3. If I continue, what make and brand of gear should I be looking at?
Before I bother with detailed directions, decide you are willing to spend the money and do the work.
Quoted message said:4. Would I be happier keeping what I have and pocket my $34 on a nice meal?
It is unlikely you'll solve the problem for $34, not to mention the fact that half-steps are
basically custom animals today. Can you get a hooker for $34?
Also, Sheldon writes on his most excellent site:
"Another serious disadvantage is that every other shift in the normal sequence is a double shift
(front and rear derailers simultaneously)."
This is more true theoretically than practically. You can skip a gear with a half-step. I do it all
the time. Yes, sometimes we make the double shift, but the upside of it is that it is an easy
double shift.
"Half-step gearing is most suitable for riding in flat terrain, where shifting is rare. For bicycles
with few speeds, it does allow finer gradations to get as close to the "ideal" gear for the
particular wind conditions as possible."
I cannot agree with this for modern systems where the rear is indexed and gated and the front shifts
are so crisp w/ the closely toothed rings. If the land is flat and the road is straight, you won't
be shifting too much with any gear system.
"Modern shift patterns use larger jumps on the chainwheels to select general ranges of gears, and
fairly closely-spaced 7-or-more-speed clusters for the fine tuning. This greatly simplifies the
shifting pattern, allowing constant adjustment to different grades in rolling terrain, with only
occasional need for double shift."
True, but the double shift of the modern crossover systems is a bit of a pain when it does finally
need to take place. The half-step double shift is much easier and quite straightforward; but you'll
be doing it a lot more often.
Mostly I think half-steps survive mainly for weirdo gear-heads like myself who like to experiment.
Most people put 9 or 10 cogs on the back, shift crossover and say "I'm done." That said, if I were
to leave on a loaded tour today, I would probably put the following on my bike:
26 42 46 11 63.818 103.091 112.909 12 58.500 94.500 103.500 14 50.143 81.000 88.714 17
41.294 66.706 73.059 20 35.100 56.700 62.100 24 29.250 47.250 51.750 29 24.207 39.103 42.828
34 20.647 33.353 36.529
I don't consider the gears on a bike used for an actual tour experimental. The half-step shouldn't
quite be dead in my opinion.
But due to evil hype marketeers and evil publically held monopolistic corporations, too little
choice exists in the marketplace. None of us weirdos can find the parts we want at the LBS. (Yes,
that was a bad joke.)