program to compute gears, with table

On Mon, 11 Sep 2017 23:12:48 -0400, Frank Krygowski
wrote:

On 9/10/2017 1:21 AM, John B. wrote:
On Sat, 09 Sep 2017 08:58:17 -0500, AMuzi wrote:

On 9/8/2017 4:23 PM, wrote:
On Friday, September 8, 2017 at 10:45:07 AM UTC-7, Emanuel Berg wrote:
Graham wrote:

So if your definition of gear is roll out in
mm then it looks close. Do not forget to
include the tyre.

Right, perhaps I should change "gear" into
"roll out" if that's the agreed-upon term.
Perhaps I should even make it print the
formulae first thing.

And I'll include the tyre. Excellent

There's always a slight error this way. The radius of a tire and hence it's circumference changes slightly with pressure and/or weight of the rider.


The ancient and traditional method from race-rules gear
limits to computer input is a rollout.
Ride over a spot of paint and measure between marks. In
theory it's 2R*3.14159. In practice it is not. As you note,
rider weight, inflation etc have some bearing on this

Disregarding "gear inches" I found a sequel to the Freakonomics book
called "SuperFreakonomics" It gets into the economics of street
prostitution early on in the book :-)

Yes, that was interesting too. But she wasn't a street prostitute. She
was a high-priced call girl. With a degree in economics, as I recall!

Ah, you didn't read the whole book.

The introduction mentioned a $300/hour "Escort" named Allie, and then
Chapter 1 described LaSheena who was a street girl and a later chapter
described Allie's business. An interesting point was that while
business was poor for the Street Girls the Escort kept raising her
prices with no loss of business :-)
--
Cheers,

John B.

On 9/11/2017 10:52 PM, Emanuel Berg wrote:
John B. wrote:

On one hand you are reciting what the
specifications are telling you and on the
other hand it is a bloke with years and years
of experience in the business is telling you.

Shozaburo Shimano founded Shimano in
February 1921 which amounts to a collective
experience of 96y 7m 11d, and not of the
business in general, but of manufacturing
bicycle parts. And they say 6/7/8 of their
own chain.

The other people/shops I've refered to who
also say this are probably just repeating what
Shimano says on the chain box.

And I think that's completely natural! I also
trust what manufacturers of an international
magnitude like Shimano put on their boxes.
First thing with new gear I always read on
the box.

So even tho I never tried it myself (a
6/7/8 chain on a 6 casette) I dare say yes,
I find this story a bit strange.


As with SRAM, it was called an 8 chain until they stopped
making the wider models. Those are still available, not any
more expensively, just not from those two vendors.

--
Andrew Muzi
www.yellowjersey.org/
Open every day since 1 April, 1971

On Monday, September 11, 2017 at 8:05:33 PM UTC-7, John B. wrote:
On Mon, 11 Sep 2017 16:00:39 +0200, Emanuel Berg
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.

And I remember a "payroll program" that we developed in Pascal that
ran so slowly that we had to rewrite nearly all the in/out stuff in
assembler.

You want to go back to writing code for a single core CPU screaming
along at 1 Mhz :-)

About the only improvements you can get with assembly language is servicing RTOS calls. I needed assembly language programs because I was doing very complex and tedious programs that manipulated 16 axis in a chemical analysis instrument using an 8008. But today's fast processors make that unnecessary. Plus today I would design multiple processors into any complex instrument since they are cheap.

John B. wrote:

Because, as Andrew told you, it will fit.
On the other hand, as Andrew told you, if a 6
speed it won't shift well.

I think it would make more sense if Shimano put
just one digit, or one set of digits, on their
boxes, which refered both "fits" and "shifts
well".

It is the intuition as well.

For example if I had a 6 casette from Shimano,
then put on a 6/7/8 chain, and it didn't shift
well, the thought wouldn't hit me the
chain/casette combination could be the problem,
but I suppose one will have to get used to
disinformation even from the most
iconic manufacturers.

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

AMuzi wrote:

As with SRAM, it was called an 8 chain until
they stopped making the wider models.
Those are still available, not any more
expensively, just not from those two vendors.

Does that mean the 6/7/8 chain shouldn't be
used for 7s as well? Just not as bad as on a 6?

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

On Tuesday, September 12, 2017 at 3:53:29 AM UTC-4, John B. wrote:
On Tue, 12 Sep 2017 06:00:09 +0200, Emanuel Berg
wrote:

Sir Ridesalot wrote:

Many times he asks a question then disagrees
with what those experts like Andrew who know
the RIGHT answer tell him.

So let's hear it, why do Shimano put such
obvious disinformation on their product boxes?

Because, as Andrew told you, it will fit. On the other hand, as Andrew
told you, if a 6 speed it won't shift well.

I might add that I have used a 10 speed chain with a 9 speed cassette
and a 9 speed chain with a 10 speed cassette, and they worked to my
satisfaction although Shimano certainly do not state it will work on
the box.

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

- Frank Krygowski

Frank Krygowski wrote:

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

Another aspect of this, do you need/want
different chain breakers for 1, 6, 7, 8, 9, 10,
11, and 12 speed chains or does the bushing
diameter stay the same, or at least doesn't
vary to the point it matters?

On my tool it says "For all speed chain" but
its asaklitt, a brand I trust considerably less
than Shimano...

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

Frank Krygowski wrote:

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

But is that incorrect as long at it works great
with 9? (If indeed it does.)

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

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.
--

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".

--