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#11
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casette shifting, again
On Wed, 12 Dec 2018 21:24:57 -0500, Frank Krygowski
wrote: On 12/12/2018 5:29 PM, Theodore Heise wrote: On Wed, 12 Dec 2018 17:15:45 -0500, Frank Krygowski wrote: On 12/12/2018 4:58 PM, Emanuel Berg wrote: I thought the general problem was the cable loosed its integrity or internal strength, so it got just a bit longer, much like a bicycle chain, but enough to mess things up? The cable itself is not going to get stretched with use, if that's what you mean. That would require forces many, many times larger than what's being applied in normal operation. I think that's correct, and yet on my tandems I've sometimes seem some changes in shifting that I attribute to change in cable length--maybe more due to temperature changes than to actual physical stretching. For example, when we go out on a very warm day after having ridden in cold weather for a time, I often have to tighten the adjuster just a smidge. I think apparent increases in cable length are probably due to shifting of position of the cable inside the housing, or wear of the housing where the cable follows it through curves, or the end of the housing settling further into a housing stop. Maybe the temperature change triggers something like that? As I've mentioned, my most frequent index shifting adjustment happens with my folding bike, especially if its sat folded for a while. I've learned it's easiest to just change the levers to friction mode for a while, then re-try the index mode. Somehow, most of the misadjustment corrects itself - I guess by the cables settling into their old equilibrium position. I'm pretty sure that if it were feasible to run the shift cable through a straight, rigid tube all the way from shifter to derailleur, I'd never see that problem. If you are going to use rigid tubes why not a rod? Similar to the old rod operated brakes. :-) cheers, John B. |
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#12
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casette shifting, again
Rod brakes: you mean like this? [1] It is a Flying Pigeon, which I won't bother saving.
Shifting: more snow, still works. The new cable did it. Only I don't know why. Also I don't know if this cable needs lubing. Next time, will investigate closer. [1] http://user.it.uu.se/~embe8573/bike/...rear-brake.jpg |
#14
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casette shifting, again
On 12/14/2018 11:34 PM, John B. Slocomb wrote:
On Fri, 14 Dec 2018 20:17:29 -0800 (PST), wrote: Rod brakes: you mean like this? [1] It is a Flying Pigeon, which I won't bother saving. Shifting: more snow, still works. The new cable did it. Only I don't know why. Also I don't know if this cable needs lubing. Next time, will investigate closer. [1] http://user.it.uu.se/~embe8573/bike/...rear-brake.jpg Sort of :-) When I lived in Japan all the bicycles had brakes similar to that. Actually they were pretty poor brakes mainly due to the design of the brake arms and small brake pads but the linkage worked very well and didn't stretch. Another problem was that the rims were chrome plated steel which was pretty slippery. For braking, pad size is a minor factor. It's all swept area, CF and leverage. You're right that linkage is efficient but the leverage is minimal and rubber on chromed steel has a low CF, made worse by dried hard pads. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#15
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casette shifting, again
AMuzi wrote:
For braking, pad size is a minor factor. It's all swept area, CF and leverage. You're right that linkage is efficient but the leverage is minimal and rubber on chromed steel has a low CF, made worse by dried hard pads. OK, so now it got complicated... Swept area, should that be big or small for the brake to be efficient? Small, right? As in disc brakes where say a single degree of braking on the small disc translates to a much larger distance on the big wheel? Or are disc brakes more efficient because of material interaction and other technology improvements alone? And if the linkage on rod brakes is efficient, how can leverage be minimal unless there is something wrong with the levers, and they seem pretty straightforward to me? Or is it the shackle that is pulled onto the rim, as opposed to squeezed into/around it, which is more efficient? Also, CF, is that some material interaction property? -- underground experts united http://user.it.uu.se/~embe8573 |
#16
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casette shifting, again
On 12/15/2018 1:30 PM, Emanuel Berg wrote:
AMuzi wrote: For braking, pad size is a minor factor. It's all swept area, CF and leverage. You're right that linkage is efficient but the leverage is minimal and rubber on chromed steel has a low CF, made worse by dried hard pads. OK, so now it got complicated... Swept area, should that be big or small for the brake to be efficient? Small, right? As in disc brakes where say a single degree of braking on the small disc translates to a much larger distance on the big wheel? Or are disc brakes more efficient because of material interaction and other technology improvements alone? And if the linkage on rod brakes is efficient, how can leverage be minimal unless there is something wrong with the levers, and they seem pretty straightforward to me? Or is it the shackle that is pulled onto the rim, as opposed to squeezed into/around it, which is more efficient? Also, CF, is that some material interaction property? Emanuel, with all due respect, you should spend the winter reading a physics book or two. Or three. Skip the parts on electricity, atomic physics, etc. Concentrate on forces, motion, work, energy etc. - the parts that apply to bicycles. I say that because words like "efficient" have carefully defined technical meanings, and you tend to mis-apply them. "Leverage" is perhaps less technical, but probably better expressed as "mechanical advantage." And look up "swept area" for brakes (you can google it). By CF, Andrew meant Coefficient of Friction. It's most often abbreviated with the Greek letter "mu" which is hard to type into these discussions. Really, you need more foundation in basic mechanics and physics. It will allow you to understand the relevant mechanisms and to phrase your questions much more clearly. This study will be well worth your time, and will save the rest of us time as well. -- - Frank Krygowski |
#17
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casette shifting, again
Frank Krygowski wrote:
Emanuel, with all due respect, you should spend the winter reading a physics book or two. Or three. Skip the parts on electricity, atomic physics, etc. Concentrate on forces, motion, work, energy etc. - the parts that apply to bicycles. [...] Blah blah blah, you have told me this at least a dozen times by now. Probably because it is easier to be didactic/demeaning than to actually answer the questions. -- underground experts united http://user.it.uu.se/~embe8573 |
#18
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casette shifting, again
On 12/15/2018 3:04 PM, Emanuel Berg wrote:
Frank Krygowski wrote: Emanuel, with all due respect, you should spend the winter reading a physics book or two. Or three. Skip the parts on electricity, atomic physics, etc. Concentrate on forces, motion, work, energy etc. - the parts that apply to bicycles. [...] Blah blah blah, you have told me this at least a dozen times by now. Probably because it is easier to be didactic/demeaning than to actually answer the questions. Sincerely, Frank's advice is excellent. Visit a used book store and find a basic physics textbook. It's well worth a few Krona and a few hours of your time, if only to posit questions here! -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#19
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casette shifting, again
On 12/15/2018 3:04 PM, Emanuel Berg wrote:
Frank Krygowski wrote: Emanuel, with all due respect, you should spend the winter reading a physics book or two. Or three. Skip the parts on electricity, atomic physics, etc. Concentrate on forces, motion, work, energy etc. - the parts that apply to bicycles. [...] Blah blah blah, you have told me this at least a dozen times by now. Probably because it is easier to be didactic/demeaning than to actually answer the questions. more. I left school without having slept through even one physics class. My reference work here is a 1955 high school textbook for $1 (9 Kr). I don't know all of even that, but I understand the world well enough to know that this headline last week: https://www.dailymail.co.uk/sciencet...soon-2022.html was completely ridiculous. The chamber pressures are in the same range, but not power, not even within a magnitude*! Power is work over time. Without some grasp of the actual world, you would not have laughed aloud when reading the headline, etc. *A typical 120mm tank round is 7.5 kilos of depleted uranium moving at 1700 m/s. The new 6.8 rifle typically moves 7.5 grams at 850 m/s. That's why you need basic physics. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#20
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casette shifting, again
AMuzi wrote:
Blah blah blah, you have told me this at least a dozen times by now. Probably because it is easier to be didactic/demeaning than to actually answer the questions. Sincerely, Frank's advice is excellent. Visit a used book store and find a basic physics textbook. It's well worth a few Krona and a few hours of your time, if only to posit questions here! I spent 6 years, 7 months, and 12 days at the university. My degree project [1] is 153 pages. I solved the same problem five other guys did at two North-American universities. I don't have to prove to anyone I can read and understand whatever I put my mind to. In fact, this has nothing to do with any of this. This is the bike culture which for whatever insane reason is snobbish beyond belief. You can all try this out for yourself. Install Emacs, use it until you run into a problem, then go to gnu.emacs.help and ask about it. If you get the answer "you are not using the terminology correctly, go read a book, then come back" please show it to me, as, in all my years in computing, I've never ever seen that. [1] http://user.it.uu.se/~embe8573/hs-li...ort/report.pdf -- underground experts united http://user.it.uu.se/~embe8573 |
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