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#101
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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 |
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#102
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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
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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
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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
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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
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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
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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
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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
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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
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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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