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program to compute gears, with table



 
 
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  #101  
Old September 13th 17, 03:58 AM posted to rec.bicycles.tech
Sir Ridesalot
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Posts: 3,553
Default program to compute gears, with table

On Tuesday, September 12, 2017 at 10:02:10 PM UTC-4, Emanuel Berg wrote:
John B. wrote:

There is no disinformation at all. The chain
will fit 6,7,8 speed cassettes. And that is
just what they told you.


I can't speak for anyone else, but I'm
interested in equipment that works and works
well, and if it doesn't, I don't care if it
fits or not.

--
underground experts united
http://user.it.uu.se/~embe8573


DUH! If it doesn't fit well then how in blazes do you expect it to work well?

Cheers
Ads
  #102  
Old September 13th 17, 05:13 AM posted to rec.bicycles.tech
Frank Krygowski[_2_]
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Posts: 6,917
Default program to compute gears, with table

On Tuesday, September 12, 2017 at 6:48:12 PM UTC-4, wrote:
On Tuesday, September 12, 2017 at 11:58:38 AM UTC-7, Frank Krygowski wrote:

Didn't Shimano advertise derailleurs as being "9 Speed" when they were precisely
the same geometry as their previous derailleurs?


I'm not sure of that Frank. I think that the angles were improved over time. I know that I have a Campy long arm rear derailleur that doesn't shift as well as a short arm newer model. The way the arms rotate and drop are much better on the short arm. That seems to be my experience with the Shimano stuff as well.


Well, there's this from http://www.sheldonbrown.com/harris/derailers-rear.html

"How Many Speeds?
Rear derailleurs often are referred to as "7-speed", "8-speed" or "9-speed." This is not as important a distinction as it might appear. Current model derailers are pretty much interchangeable within brands. A "7-speed" or "8-speed" designation generall just indicates that the derailer is an older design, or a cheaper model. They'll all work with all 3 systems, though the models marked "9-speed" will generally be slightly better (whatever cluster you use.)"

But Sheldon (or John) does say "pretty much interchangeable," so I suppose there
are some differences.

From the same page:

"NEW! SunXCD 8/9/10-Speed Rear Road Derailleur GS RD1105 $119.95 buy button

"The SunXCD Rear Road derailer can handle up to a 34t cog and is 8/9/10 speed compatible!

"Why do we think this is cool? Read on. . .

"Now you can run up to a 34t cassette cog with 7, 8, 9, or 10-speed STI levers.

" Up through 9-spd systems, Shimano Road and MTB shifters and derailers were interchangeable. So it was possible to use an MTB rear derailer and wide range cassette with STI shifters. All that changed with the introduction of 10 speed drive trains. With 10 speed Shimano, road is road, and MTB is MTB. They don't play nicely together. This derailer solves the 10-speed incompatibility issue. And being shiney silver rather than matte grey paint doesn't hurt one bit. . .

"SunXCD is a new company founded by the former president of Suntour Japan."

So I guess things have gotten more complicated recently.

- Frank Krygowski

  #103  
Old September 13th 17, 08:28 AM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 355
Default program to compute gears, with table

Sir Ridesalot wrote:

DUH! If it doesn't fit well then how in
blazes do you expect it to work well?


Mind-boggling, indeed! How did I ever come to
expect that the 6/7/8 chain would work well on
a 6 casette?

Now, if you guys say 6/7/8 is incorrect, that
it is actually an "8 and only 8" chain which
has been incorrectly rebranded for commercial
"inventory reduction" reasons, I suggest you
direct the heat toward Shimano.

--
underground experts united
http://user.it.uu.se/~embe8573
  #104  
Old September 13th 17, 04:31 PM posted to rec.bicycles.tech
[email protected]
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Posts: 2,872
Default program to compute gears, with table

On Tuesday, September 12, 2017 at 5:13:45 PM UTC-7, Emanuel Berg wrote:
Here is what Wikipedia says: [1]

With derailleur equipped bicycles, the
external width of the chain also matters,
because chains must not be too wide for the
cogset or they will rub on the next larger
sprocket, or too narrow that they might
fall between two sprockets.

Chains can also be identified by the number
of rear sprockets they can support,
anywhere from 3 to 11, and the list below
enables measuring a chain of unknown origin
to determine its suitability.

* 6 speed – 7.8 mm (5/16")
* 7 speed – 7.3 mm (9/32")
* 8 speed – 7.1 mm (9/32")
* 9 speed – 6.6 to 6.8 mm (1/4 to 9/32")
* 10 speed – 6.2 mm (1/4") (Shimano, Campagnolo)
* 10 speed (Narrow) – 5.88 mm (7/32") (Campagnolo, KMC)
* 10 speed (Narrow, Direction) – 5.88 mm (7/32") (Shimano CN-5700, CN-6700, CN-7900)
* 11 speed – 5.5 mm (7/32") (Campagnolo, KMC, Shimano CN-9000)

Interesting that the 7 and 8 are the same in
inches, but not in mm.

$ units -t '7.3 mm' '1|32 in'
9.1968504

$ units -t '7.1 mm' '1|32 in'
8.9448819

[1] https://en.wikipedia.org/w/index.php...&printable=yes


Presenting actual facts is not allowed on this group. You're supposed to be someone that last rode a bike in 1972 and have a vague recollection of what their bike repair guy told them they think.
  #105  
Old September 13th 17, 04:38 PM posted to rec.bicycles.tech
Joy Beeson
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Posts: 954
Default program to compute gears, with table

On Tue, 12 Sep 2017 10:31:56 +0700, John B.
wrote:

Something I've always wondered about is how in the world can I ride an
out and back course and have a head wind both ways :-(


I've often thought that bicycle conventions should be combined with
hang-glider conventions. Each morning when the riders fan out in all
directions, each one pedalling into a headwind, there is going to be a
mighty updraft in the middle.

--
Joy Beeson
joy beeson at comcast dot net
http://wlweather.net/PAGEJOY/

  #106  
Old September 13th 17, 05:53 PM posted to rec.bicycles.tech
Doug Landau
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Posts: 1,215
Default program to compute gears, with table

On Wednesday, September 13, 2017 at 9:38:46 AM UTC-7, Joy Beeson wrote:
On Tue, 12 Sep 2017 10:31:56 +0700, John B.
wrote:

Something I've always wondered about is how in the world can I ride an
out and back course and have a head wind both ways :-(


I've often thought that bicycle conventions should be combined with
hang-glider conventions. Each morning when the riders fan out in all
directions, each one pedalling into a headwind, there is going to be a
mighty updraft in the middle.



THAT
.... is heavy
  #107  
Old September 13th 17, 06:12 PM posted to rec.bicycles.tech
Radey Shouman
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Posts: 935
Default program to compute gears, with table

John B. writes:

On Tue, 12 Sep 2017 16:19:21 -0400, Radey Shouman
wrote:

John B. writes:

On Mon, 11 Sep 2017 08:23:48 -0700 (PDT), wrote:


[ ... ]

Yesterday I rode on a 35 mile ride. On the way out into a headwind I
averaged a little less than 14 mph. I had a cup of coffee while in
the city square the worst band I ever heard was making awful
noises. When I was in a band if we had played that badly on our
first try in a rehearsal we would have quit.

On the way back the wind had reversed and I had a hard time
maintaining 12 mph for most of the way. By the time I got home I was
exhausted. Do you think that I could improve my performance with an
11 or 12 speed?

I know my limits and it isn't playing as if I was Chris Froome.

Something I've always wondered about is how in the world can I ride an
out and back course and have a head wind both ways :-(


With some reasonable assumptions I think you can show that this is
actually true, in a sense. Suppose for example the wind is blowing at
right angles to your (perfectly straight) direction, and that it happens
to be blowing at exactly your ground speed, v.

The apparent wind will be at 45 degrees your heading, at a velocity of
sqrt(v^2 + v^2) = sqrt(2)*v.

For turbulent flow, the drag force is approximately proportional to the
square of the wind speed, so the drag force will be twice the drag force
you would see in still air, F. (At this point we have assumed a
cylindrical bike & rider, meaning that the coefficient of drag is the
same from the front as the side, since drag from the side is normally
greater, this is conservative).

Fortunately the drag force acts at 45 degrees to your course, so the
drag component that holds you back is
cos(45 deg)*F = (2/sqrt(2))*F
= sqrt(2)*F
~= 1.414 F

This is as true on the way out as it is on the way back, hence you
really do have an effective head wind both ways.


I was thinking of days when I ride what I call my short route. It is a
square loop in the city on which the two longer legs are essentially
due north and due south. I set out and on the south leg the wind was
directly in my face. then the "cross wind" leg, about 1 km and
protected by tall buildings and then the north bound leg. Again wind
directly in my face. There are traffic lights on both the north and
south legs and the wind doesn't stop blowing when I stopped at a red
light :-)


I suspect that a constant wind always slows one down over a closed loop.
Almost certainly true if you ride straight into the wind and then
straight back. Supposing you're a real hard ass, and ride the speed of
the wind both ways: The trip out has four times the drag force, the
trip back zero. Net over the course is twice the drag force.

--
  #108  
Old September 13th 17, 06:15 PM posted to rec.bicycles.tech
Radey Shouman
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Posts: 935
Default program to compute gears, with table

John B. writes:

On Tue, 12 Sep 2017 16:30:42 -0400, Radey Shouman
wrote:

John B. writes:

On Tue, 12 Sep 2017 06:06:56 +0200, Emanuel Berg
wrote:

John B. wrote:

That isn't true at all. I have definitely
improved the speed of a C program by using an
assembler language sub routines and even had
two C compilers that would compile the same
program into two different sizes that
performed the same "test" program at two
different speeds.

Obviously two different programs will be of
different sizes and run at different speeds.

But that wasn't what I said at all. As I said the same code compiled
on two different compiler resulted in both a different size compiled
application and, as well, a speed difference when running.

With compilers to do optimization, and with
much increased hardware to make optimization
unnecessary to begin with, there is close to
zero gain re-writing C into assembler, and its

Except when it does make a difference.

an undertaking that isn't proportional to that
gain. So it is rather done when there is a need
to manipulate hardware directly or in ways
which the high-level language isn't suited for.

I'm not sure that is correct in all cases although of course modern
computers run at speeds that make the slower software appear to be
satisfactory. But I did a search on the question "is modern software
written in assembler" and the first hit replied:

"Probably more than most people think, especially in the
microcontroller field. I write in assembler when it's appropriate,
which for the kind of work I do is most of the time


I write in assembler every day, not on any rational basis, but because
that's how my boss did it back in the day.

The big difference between new processors and old, from my point of
view, is the much deeper instruction pipelines. In order to get the
most from these machines one should write in the least straightforward
way possible, doing a little of this, then a little of that, so that
there is as long a time as possible between setting some register's
value and using it. Compilers are good at this, human beings not so
much, especially when the code has to be debugged and modified at some
time in the unknowable future.

On the other hand, in assembler one may use the low level processor
behavior to make sure things are done in an efficient way -- for example
carry and overflow conditions are straightforwardly but non-portably
checked. In C, if you want to make sure the compiler does what you
think it should you have to check the generated assembly, and possibly
contort your code to make your intention "clear".


Ultimately I disassembled the two test programs from the two different
C compilers and found that the difference between the two was that the
Microsoft compiler saved the state, all the registers, etc., then
called the "sub routine" then recovered the state, all the registers,
etc., and went on to the next step. A sort of bullet proofing I guess
you'd call it. The other compiler apparently figured that the
programmer knew what he was doing and if you wrote "write("Good
Morning\n");" it just went ahead and did it.


That's called "inlining". Not possible with compiled library routines,
and increases code size, sometimes dramatically. Can also worsen icache
behavior, sometimes to the point of running slower.


--
  #109  
Old September 13th 17, 06:22 PM posted to rec.bicycles.tech
Radey Shouman
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Posts: 935
Default program to compute gears, with table

Emanuel Berg writes:

Radey Shouman wrote:

the much deeper instruction pipelines


"deeper instruction pipelines", is that like
the many transformations of graphical data
before it appears on the screen, or a shell
parsing of a text string with UNIX tools,
i.e. done_value=$(a | b | ... | n) ? If so, are
the extra steps because of new capabilities the
CPU has that wasn't there before?


Only very approximately. A pipelined processor speculatively begins
executing one instruction before the previous one has finished. Each
instruction requires a sequence of steps: fetching the instruction from
cache, decoding, fetching the operands, doing the operation, storing to
destination ... The processor I am writing for at the moment has an 8
stage pipeline, meaning that an instruction that might have taken 8
cycles to execute in the stone ages of computing, when John and Tom were
still carrying lunchboxes, might execute in only one cycle, *if*
everything goes smoothly.

Often things do not go smoothly, for example, some earlier instruction
might modify a value needed as an operand for a later instruction,
causing a pipeline stall. Obviously branches are a disaster -- modern
processors try to predict which branch will be taken, and continue
speculative execution there. Some processors allow instructions to live
in one or more "delay slots", and are unconditionally executed after a
branch regardless of whether it is taken or not.

Back in the day you could just look up the number of cycles required by
your instructions, add them up, and know how long some operation would
take. Not any more, now you have to either try it, or use a
cycle-accurate simulator.


--
  #110  
Old September 13th 17, 08:46 PM posted to rec.bicycles.tech
Emanuel Berg[_2_]
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Posts: 355
Default program to compute gears, with table

cyclintom wrote:

Presenting actual facts is not allowed on
this group. You're supposed to be someone
that last rode a bike in 1972 and have
a vague recollection of what their bike
repair guy told them they think.


Fun comment, true or not

--
underground experts united
http://user.it.uu.se/~embe8573
 




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