Shimano 105 half step?

[Mike Jacoubowsky]

>> Back in the day, when I was a half-step afficianado, I used to machine
>> down the part of the crank spider where the chainrings mounted, which
>> resulted in dramatically-improved shifting. If you wish to try this, make
>> sure you remove material on the *outside* face, since otherwise you might
>> create too large a gap for the middle-small shift (on a half-step plus
>> granny).
>>
>
> Hi Mike,
>
> Smart solution. Do you recall how much metal you had to take off, or
> would this be more of a trial and error process?
>
> Cheers,
> Angus

It was most definitely trial & error. And a fair amount of error, such that
once in a while one had to use a very thin shim because too much material
was removed. I'm not a machinist, and what I forgot to mention (because I
had literally forgotten) was that I gave up on removing material from the
crank spider and filed down the chainring (where it mounts) instead. Much
safer (less risk of destroying something expensive) & easier to control.

--Mike-- Chain Reaction Bicycles
www.ChainReactionBicycles.com


"angus" <[email protected]> wrote in message
news:Nmnle.1488225$8l.228842@pd7tw1no...
> Mike Jacoubowsky wrote:
>
>>
>> Back in the day, when I was a half-step afficianado, I used to machine
>> down the part of the crank spider where the chainrings mounted, which
>> resulted in dramatically-improved shifting. If you wish to try this, make
>> sure you remove material on the *outside* face, since otherwise you might
>> create too large a gap for the middle-small shift (on a half-step plus
>> granny).
>>
>
> Hi Mike,
>
> Smart solution. Do you recall how much metal you had to take off, or
> would this be more of a trial and error process?
>
> Cheers,
> Angus
>

 

[juicemouse]

angus wrote:
> My current crankset is a Shimano 105 triple, 52-42-30 (130/74 BCD). I
> want to switch to half step gearing, namely 52-48-30.


I'm a little confused about the use of half-step on a loaded touring
bike. From my touring experience, I would think that your critical
gears would be your lower ones, and that your taller gears wouldn't be
as important because they only limit your top speed. Also take into
account that the jump in gearing in the cassette is always bigger for
the low gears than it is for the tall ones. Wouldn't it make more
sense to have your low and middle front chainrings be closer together,
so as to give you more low gear variations (I'm thinking 52-34-30 for
the OP)? I'm just not seeing on a typical half-step setup how
cross-chaining from the two tall front chainrings to the lower gears on
the cassette (especially when using a wide 8 or 9 speed cassette) to
get more variation in low-end gearing makes much sense. Are the people
who use such setups not as interested in low-end gearing for some
reason? I could see being interested in more top-end gearing variation
on a racing bike, but for loaded touring? Even with the OP's 20"
wheels, wouldn't it be the entire gear -range- that he'd want to shift
higher relative to 700c wheels, and not just focus primarilly on his
highest gears?

 

[angus]

juicemouse wrote:
> angus wrote:
>
>>My current crankset is a Shimano 105 triple, 52-42-30 (130/74 BCD). I
>>want to switch to half step gearing, namely 52-48-30.
>
>
>
> I'm a little confused about the use of half-step on a loaded touring
> bike. From my touring experience, I would think that your critical
> gears would be your lower ones, and that your taller gears wouldn't be
> as important because they only limit your top speed. Also take into
> account that the jump in gearing in the cassette is always bigger for
> the low gears than it is for the tall ones. Wouldn't it make more
> sense to have your low and middle front chainrings be closer together,
> so as to give you more low gear variations (I'm thinking 52-34-30 for
> the OP)? I'm just not seeing on a typical half-step setup how
> cross-chaining from the two tall front chainrings to the lower gears on
> the cassette (especially when using a wide 8 or 9 speed cassette) to
> get more variation in low-end gearing makes much sense. Are the people
> who use such setups not as interested in low-end gearing for some
> reason? I could see being interested in more top-end gearing variation
> on a racing bike, but for loaded touring? Even with the OP's 20"
> wheels, wouldn't it be the entire gear -range- that he'd want to shift
> higher relative to 700c wheels, and not just focus primarilly on his
> highest gears?
>

Agreed, the crucial gears are the lower ones. And the elegance of half
step gearing is that it offers small gear jumps across the entire range
of your cluster. Not just for higher gears, not just for the lower
gears, but for all of them.

The mathematical reason half-step works is that the gear spacing on the
cluster is (almost) always a geometric progression, meaning that each
gear has N percent more teeth than the one beside it. The relationship
can never be exact because we're dealing with integer arithmetic, but
it's close. In the case of my 11-32 the steps are 8.7% between the 11
and 12, then become 15.4%, 13.3%, 11.8%, 15.4%, 13.3%, 15.4%, and 13.3%.
When the bike is unloaded I can live with these big jumps even though
there are many times I wish for a gear that's "in-between". When I'm
loaded and heading uphill or into the wind the story is different.

The average step size works out to 14%. Therefore the difference in the
number of teeth in the chain rings should be half that, 7%.

52-48 rings work out to 8%, close enough. My problem was in finding a
48T-130 middle ring. They're available, but expensive.

So I'm going back to an old 110-74 crank with inexpensive 46-43-24 8-spd
rings and Mike J's modification to prevent the 9-spd chain from dropping
between the rings. This setup will give me steps of 5% to 8.7% from 27"
to 84", plus granny down to 15".

As far as trying 52-34-30, besides being unnecessary, you'll never find
a 34T ring for 130mm bcd, although something might be do-able using a
Mountain Tamer Quad setup. Interesting thought. . Try it and let us
know how well it works.

Cheers,
Angus

 

[dvt]

angus wrote:
> juicemouse wrote:
>> angus wrote:
>>> My current crankset is a Shimano 105 triple, 52-42-30 (130/74 BCD). I
>>> want to switch to half step gearing, namely 52-48-30.

>> I'm a little confused about the use of half-step on a loaded touring
>> bike. From my touring experience, I would think that your critical
>> gears would be your lower ones,... Wouldn't it make more
>> sense to have your low and middle front chainrings be closer together,
>> so as to give you more low gear variations (I'm thinking 52-34-30 for
>> the OP)?

> Agreed, the crucial gears are the lower ones. And the elegance of half
> step gearing is that it offers small gear jumps across the entire range
> of your cluster. Not just for higher gears, not just for the lower
> gears, but for all of them.

> So I'm going to... This setup will give me steps of 5% to 8.7% from 27"
> to 84", plus granny down to 15".

Angus, I don't understand. Your setup will get closely spaced gears
between 27 and 84", widely spaced gears from 15-27". Juicemouse is
asking why you wouldn't set it up the other way -- say, for example,
closely spaced gears from 15-50" and widely spaced gears from 50-82"?

I'm not experienced in loaded touring, but I think you'd spend more time
in the 50-82" range than the 15-27" range. If closely spaced gears are
what you seek, it would seem to make sense that you'd put the closely
spaced gears in the area where you spend the most time.

--
Dave
dvt at psu dot edu

 

[pinnah]

dvt <[email protected]> wrote:
>I'm not experienced in loaded touring, but I think you'd spend more time
>in the 50-82" range than the 15-27" range. If closely spaced gears are
>what you seek, it would seem to make sense that you'd put the closely
>spaced gears in the area where you spend the most time.

I'm going from memory here so I could be a bit off on the exact numbers....

When I was doing a lot of loaded touring, I wanted as many gears as close
together as possible in the 35" - 85" range. This, for me, was the meat of
what I wanted for seated pedling with a full load on flat to rolling
terrain.

There is no real need for high gears above 85" imo. This is rolling down
the hill territory and I go fast enough with a big load that I don't want
to push things faster. YMMV.

IMO, there is no need for lots of choices for gears lower than 30". For
seated climbing, I want a 24T (or smaller) granny and the 3 biggest cogs on
the back, with a 32T as a desirable min (some folks insist on a 34T).

Small differences in the gears in the mid range helps more than you can
imagine. Headwinds, minor changes in grade.... these are things you (ok, I)
want to deal with with a gearing change, not more muscle.

The thing with 1/2-step gearing is that you get 2n - 2 useful and
*distinct* gears, where n is the number of rear cogs. With alpine gearing,
you usually get n + 2 to n + 4 distinct, non-overlapping gears.

Sure costs a lot though. TA seems to be the only good source of a wide
selection of chain rings and boy, they are pricey.

You also pay a cost of constant double shifts. Interestingly, I find this
constant double shifting to be easier with DT shifters than I do with
barends. Again, YMMV.

 

[[email protected]]

dvt wrote:
> angus wrote:
> > juicemouse wrote:
> >> angus wrote:
> >>> My current crankset is a Shimano 105 triple, 52-42-30 (130/74 BCD). I
> >>> want to switch to half step gearing, namely 52-48-30.
>
> >> I'm a little confused about the use of half-step on a loaded touring
> >> bike. From my touring experience, I would think that your critical
> >> gears would be your lower ones,... Wouldn't it make more
> >> sense to have your low and middle front chainrings be closer together,
> >> so as to give you more low gear variations (I'm thinking 52-34-30 for
> >> the OP)?
>
> > Agreed, the crucial gears are the lower ones. And the elegance of half
> > step gearing is that it offers small gear jumps across the entire range
> > of your cluster. Not just for higher gears, not just for the lower
> > gears, but for all of them.
>
> > So I'm going to... This setup will give me steps of 5% to 8.7% from 27"
> > to 84", plus granny down to 15".
>
> Angus, I don't understand. Your setup will get closely spaced gears
> between 27 and 84", widely spaced gears from 15-27". Juicemouse is
> asking why you wouldn't set it up the other way -- say, for example,
> closely spaced gears from 15-50" and widely spaced gears from 50-82"?
>
> I'm not experienced in loaded touring, but I think you'd spend more time
> in the 50-82" range than the 15-27" range. If closely spaced gears are
> what you seek, it would seem to make sense that you'd put the closely
> spaced gears in the area where you spend the most time.
>
> --
> Dave
> dvt at psu dot edu

The problem of explaining half step plus granny gearing to people who
don't understand half step plus granny gearing and have never ridden a
loaded touring bike.

With a loaded touring bike, any change in wind or road slope, has a big
affect on the rider. You need lots of closely spaced medium gears to
maintain a constant, pleasant cadence. Half step gearing allows you to
know exactly where the next easiest or hardest gear is in the shifting
pattern. There is no jumping about on the rings and cassette trying to
find the right gear.

Low gears come from the granny part of half step plus granny. You only
need 2 or 3 low gears. The important thing is they are low enough.
Once you are on the granny ring, you just shift the rear derailleur up
and down the cassette. Usually just the biggest 2-3 cogs. Having them
closely spaced is not really necessary. It usually happens that way
because the inner ring is small so jumps between cogs are small in gear
inches. But as long as the lowest is low enough, everything is OK.

My half step plus granny setup is 45-42-20 chainrings. 7.1%
difference. 14-16-18-21-24-28-32 cassette cogs. Average of 14.8%
difference. When shifting in the half step pattern, the gear inches
are 87-81-76-71-67-63-58-54-51-47-43-41-38-35. Lots of closely spaced
medium gears in a consistent shifting pattern. The granny ring then
adds gears of 39-34-30-26-23-19-17 gear inches. The shifting pattern
for the granny is straight up and down the cassette.