#11
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Cross shiftting
On Jul 16, 9:57*pm, " wrote:
On Jul 16, 7:30*am, John B. Slocomb wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. Sheldon Brown has a gear "visualizer", and there's another one called "Gerz" that makes charting pretty easy. It seems to me that with the 30/42/52 triple I have, run against 8sp and 9sp cassettes with 13-23 or 14-26t cog spreads, you wind up with gear ratios that favor running the two or three cogs most in line with both the inner and outer rings, while the middle ring works over four or five cogs, overlapping so to speak with the inner and outer rings on one cog. It's been a few years, maybe I'm misremembering but I think this "question" pretty much takes care of itself in practice if you will. Meaning, you're keeping the chain fairly straight while you use "same ratios" (or close duplicates) of gears you might find by "crossing" farther on any of the ring/cog combinations. Not to say you shouldn't "be able" to use any cog/chainring combination without either drooping the chain (which invites unshipping and/or dragging in the dirt) or binding/breaking the rear derailleur due to too short a chain, but why not use the chain in happier combinations? --D-y Well... I went back to Sheldon and did the numbers. The numbers don't "work" as far as duplicate gears or even steps between chainwheel "ranges". That part I blew out my wazoo, if that is a plain enough mea culpa. "Way off on that one". I did ride an 8sp triple with 30/42/52 chainrings and a 12-23 cassette (12, 13, 14, 15, 17, 19, 21, 23) for "a season", a couple of years ago. I found, in use, that pairing the 30t ring with the 23 and 21, shifting to the 42 for the middle five cogs, and using the 52 with the last two (or maybe three) cogs worked in "real life", for my solo riding and with "fast recreational groups". This might be partly due to the fact that I used 42/52 or 53 chainrings for about 25 years or so before changing to the "new" 39/5x arrangement. I didn't realize how much I missed the 42 until I had it to use again. I'm not even vaguely interested in a "double shift" arrangement by whatever name, having tried one once or twice way back in the day. Some people like them and more power, each to their taste, that's why they make different components, etc. etc. --D-y |
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#12
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Cross shiftting
Lou Holtman wrote:
Middle ring should shift any cogs. Large chainring avoid two largest cogs; small chainring avoid two smallest cogs. It is that simple. Yes, but this presumes neutral chainline (middle ring aligns with the middle rear sprocket). Many MTBs these days have terrible chainline, where the crank is shifted as much as two gears to the outside. This avoids much rubbing of the chain on the adjacent sprocket when in small-small combinations, but it means that the chainline in large-large combinations is even more extreme. In these circumstances, it is advisable to avoid the inner half of the cassette when using the large ring, and the couple of largest sprockets when using the middle ring. Not that anyone actually does so. Chalo |
#13
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Cross shiftting
On Sat, 16 Jul 2011 10:15:04 -0700 (PDT), Lou Holtman
wrote: On 16 jul, 14:30, John B. Slocomb wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. John B. Slocomb (johnbslocombatgmaildotcom) Middle ring should shift any cogs. Large chainring avoid two largest cogs; small chainring avoid two smallest cogs. It is that simple. Lou That is what I thought but having been caught out with the "It's obvious....." sort of thinking thought I'd ask. John B. Slocomb (johnbslocombatgmaildotcom) |
#14
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Cross shiftting
On Sun, 17 Jul 2011 01:17:20 -0700 (PDT), Chalo
wrote: Lou Holtman wrote: Middle ring should shift any cogs. Large chainring avoid two largest cogs; small chainring avoid two smallest cogs. It is that simple. Yes, but this presumes neutral chainline (middle ring aligns with the middle rear sprocket). Many MTBs these days have terrible chainline, where the crank is shifted as much as two gears to the outside. This avoids much rubbing of the chain on the adjacent sprocket when in small-small combinations, but it means that the chainline in large-large combinations is even more extreme. In these circumstances, it is advisable to avoid the inner half of the cassette when using the large ring, and the couple of largest sprockets when using the middle ring. Not that anyone actually does so. Chalo As I built this bike for this and that I was able to set the B.B. spacers so that the center chain ring is lined up with the #5 cog of a 9 speed cassette. John B. Slocomb (johnbslocombatgmaildotcom) |
#15
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Cross shiftting
On Sat, 16 Jul 2011 10:53:51 -0700 (PDT), thirty-six
wrote: On Jul 16, 1:30*pm, John B. Slocomb wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. John B. Slocomb (johnbslocombatgmaildotcom) I always like to think that the smallest sprocket must only be used with the outer ring and the biggest sprocket must only be used with the smallest ring. This help reduce the strains imposed on the derailleur pulley spring(s) and sometimes is the only way to shift cleanly over the entire range without having a drooping chain. Depending upon your derailleur it might be as well to limit the mid ring off the bottom two sprockets (if its a racing type der). You are correct but there are times when you are on, say the middle ring with a BIG hill just down the road and at the same time a bit more speed is possible for the next few moments and rather then shift both front and back for the next 100 M and then shift back I usually just go up a cog on the back, if it is possible, even if it turns out to be the little one. John B. Slocomb (johnbslocombatgmaildotcom) |
#16
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Cross shiftting
On Sat, 16 Jul 2011 14:11:39 -0400, "Ronsonic"
wrote: "John B. Slocomb" wrote in message .. . "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. As far as the chain and rear der are concerned all the cogs are in play from the middle ring. Not all setups will run without the chain rubbing the front der cage or big chainwheel. If you can trim the front der all's good. Both front and back are friction bar end shifters so "trimming" is not a major undertaking :-) John B. Slocomb (johnbslocombatgmaildotcom) |
#17
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Cross shiftting
On Jul 17, 2:22*pm, John B. Slocomb wrote:
On Sat, 16 Jul 2011 10:53:51 -0700 (PDT), thirty-six wrote: On Jul 16, 1:30*pm, John B. Slocomb wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. John B. Slocomb (johnbslocombatgmaildotcom) I always like to think that the smallest sprocket must only be used with the outer ring and the biggest sprocket must only be used with the smallest ring. *This help reduce the strains imposed on the derailleur pulley spring(s) and sometimes is the only way to shift cleanly over the entire range without having a drooping chain. Depending upon your derailleur it might be as well to limit the mid ring off the bottom two sprockets (if its a racing type der). You are *correct but there are times when you are on, say the middle ring with a BIG hill just down the road and at the same time a bit more speed is possible for the next few moments and rather then shift both front and back for the next 100 M and then shift back I usually just go up a cog on the back, if it is possible, even if it *turns out to be the little one. John B. Slocomb (johnbslocombatgmaildotcom) When I using a regiular spaced six speed block (1.1/4" wide) I was driving 42x14 and 42x13 (smallest) a lot of the time. Without a 16 I had difficulty using the 52 ring. Extra sprockets help, but are not the solution to greatest efficiency. A half step setup makes front shifts easy and the common middle gears are all near to straight. It's also good for those who are able to accelerate quickly or need to grab a low gear quickly because the wide range block is shifting over fewer sprockets in usually a narrower space. |
#18
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Cross shiftting
Sheldon Brown has a gear "visualizer", and there's another one called
"Gerz" that makes charting pretty easy. This one is very nice: http://www.gear-calculator.com |
#19
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Cross shiftting
In article ,
John B. Slocomb wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. I cross chain whenever I feel like it. When convenient I change over to a straighter run. Do not allow guilt to poison your life. Chains are cheap. -- Michael Press |
#20
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Cross-chaining
On 7/17/2011 10:59 PM, Michael Press wrote:
In , John B. wrote: "Cross shifting", i.e., Large chain Ring/large cassette cog or small chain ring/small cog is generally taken as a mortal sin. But with a triple chain ring what limits are made to the shift pattern when on the center ring? Assuming that the chain line through the center line of the 5th cog, on a 9 speed cassette, and the center line of the center chain ring? It appears to me that considering the actual distance between the three chain rings versus the actual distances on the cassette that the center chain ring should be able to shift to any cog without problems. I cross chain whenever I feel like it. When convenient I change over to a straighter run. Do not allow guilt to poison your life. Chains are cheap. Indeed, occasional cross-chaining will not hurt anything, unless through incompetence or poor judgement, your bicycle had a chain too short to accommodate the big-big combination, in which case you can wrap the chain and derailer into the spokes and/or bend or break the derailer hanger. -- Tºm Shermªn - 42.435731°N, 83.985007°W I am a vehicular cyclist. |
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