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#1
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Shifting problems on Stronglight 86mm BCD cranks
I recently acquired an '89 Super Galaxy tandem. This has Stronglight
cranks on, with a single 86mm BCD for a triple. The bicycle's original gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel. Of course, tandems being pretty quick, we found ourselves spinning out the 48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted it. However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. Furthermore, I intended to replace the rear hub with a 7-speed cassette hub; we plan to do the End to End on this tandem and I don't expect to be able to find 6s freewheels in the back of beyond, I have a bunch of existing 7s gear, and an 11t top sprocket would also alleviate the gear range problems. However, I'm concerned that a narrower chain will only exacerbate this problem. I'm not sure what the answer is. "New cranks" is obvious, but expensive. Returning to 48/42/28 might sort it out, but then the gearing's less useful. Another idea that springs to mind is drilling into the 52 and 42 just below the teeth on the 42, and bolting them together - both to make them slightly closer, and to make it impossible for the chain to descend below that level. Grinding down the flats that engage with the spider would also decrease the spacing, but seems pretty drastic. I'd be grateful for any advice people can offer. -- David Damerell Kill the tomato! |
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#2
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Shifting problems on Stronglight 86mm BCD cranks
On 06 Jul 2004 15:02:24 +0100 (BST), David Damerell
wrote: I recently acquired an '89 Super Galaxy tandem. This has Stronglight cranks on, with a single 86mm BCD for a triple. The bicycle's original gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel. Of course, tandems being pretty quick, we found ourselves spinning out the 48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted it. However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. Furthermore, I intended to replace the rear hub with a 7-speed cassette hub; we plan to do the End to End on this tandem and I don't expect to be able to find 6s freewheels in the back of beyond, I have a bunch of existing 7s gear, and an 11t top sprocket would also alleviate the gear range problems. However, I'm concerned that a narrower chain will only exacerbate this problem. I'm not sure what the answer is. "New cranks" is obvious, but expensive. Returning to 48/42/28 might sort it out, but then the gearing's less useful. Another idea that springs to mind is drilling into the 52 and 42 just below the teeth on the 42, and bolting them together - both to make them slightly closer, and to make it impossible for the chain to descend below that level. Grinding down the flats that engage with the spider would also decrease the spacing, but seems pretty drastic. I'd be grateful for any advice people can offer. Dear David, Could you be using an unusually thin chain? Last August, Pete Biggs asked about fatter chains for 5 and 6 speed bikes, and Dianne_1234 shamelessly published widths from 6.60mm to 8.61mm: http://groups.google.com/groups?hl=e...om%26rnum%3D29 or http://tinyurl.com/27po5 Carl Fogel |
#3
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Shifting problems on Stronglight 86mm BCD cranks
On 06 Jul 2004 15:02:24 +0100 (BST), David Damerell
wrote: I recently acquired an '89 Super Galaxy tandem. This has Stronglight cranks on, with a single 86mm BCD for a triple. The bicycle's original gearing was 48/42/28 chainrings with a 13-28 six speed rear freewheel. Of course, tandems being pretty quick, we found ourselves spinning out the 48/13 almost immediately. Hence I ordered a 52t 86mm chainring and fitted it. However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. Furthermore, I intended to replace the rear hub with a 7-speed cassette hub; we plan to do the End to End on this tandem and I don't expect to be able to find 6s freewheels in the back of beyond, I have a bunch of existing 7s gear, and an 11t top sprocket would also alleviate the gear range problems. However, I'm concerned that a narrower chain will only exacerbate this problem. I'm not sure what the answer is. "New cranks" is obvious, but expensive. Returning to 48/42/28 might sort it out, but then the gearing's less useful. Another idea that springs to mind is drilling into the 52 and 42 just below the teeth on the 42, and bolting them together - both to make them slightly closer, and to make it impossible for the chain to descend below that level. Grinding down the flats that engage with the spider would also decrease the spacing, but seems pretty drastic. I'd be grateful for any advice people can offer. Dear David, Could you be using an unusually thin chain? Last August, Pete Biggs asked about fatter chains for 5 and 6 speed bikes, and Dianne_1234 shamelessly published widths from 6.60mm to 8.61mm: http://groups.google.com/groups?hl=e...om%26rnum%3D29 or http://tinyurl.com/27po5 Carl Fogel |
#4
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Shifting problems on Stronglight 86mm BCD cranks
David Damerell wrote:
However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. Furthermore, I intended to replace the rear hub with a 7-speed cassette hub; we plan to do the End to End on this tandem and I don't expect to be able to find 6s freewheels in the back of beyond, I have a bunch of existing 7s gear, and an 11t top sprocket would also alleviate the gear range problems. However, I'm concerned that a narrower chain will only exacerbate this problem. I'm not sure what the answer is. "New cranks" is obvious, but expensive. Returning to 48/42/28 might sort it out, but then the gearing's less useful. Another idea that springs to mind is drilling into the 52 and 42 just below the teeth on the 42, and bolting them together - both to make them slightly closer, and to make it impossible for the chain to descend below that level. Grinding down the flats that engage with the spider would also decrease the spacing, but seems pretty drastic. The crankset may have been designed with wider, 5/6 speed chain in mind, where the rivets stick out more. Many chainrings are asymmetric - perhaps the 42 can be turned around, However, there is a better solution. I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. I used a tapered tap and didn't run it quite all the way through, so the screws are a tight fit. This keeps them from vibrating out. |
#5
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Shifting problems on Stronglight 86mm BCD cranks
David Damerell wrote:
However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. Furthermore, I intended to replace the rear hub with a 7-speed cassette hub; we plan to do the End to End on this tandem and I don't expect to be able to find 6s freewheels in the back of beyond, I have a bunch of existing 7s gear, and an 11t top sprocket would also alleviate the gear range problems. However, I'm concerned that a narrower chain will only exacerbate this problem. I'm not sure what the answer is. "New cranks" is obvious, but expensive. Returning to 48/42/28 might sort it out, but then the gearing's less useful. Another idea that springs to mind is drilling into the 52 and 42 just below the teeth on the 42, and bolting them together - both to make them slightly closer, and to make it impossible for the chain to descend below that level. Grinding down the flats that engage with the spider would also decrease the spacing, but seems pretty drastic. The crankset may have been designed with wider, 5/6 speed chain in mind, where the rivets stick out more. Many chainrings are asymmetric - perhaps the 42 can be turned around, However, there is a better solution. I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. I used a tapered tap and didn't run it quite all the way through, so the screws are a tight fit. This keeps them from vibrating out. |
#6
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Shifting problems on Stronglight 86mm BCD cranks
Benjamin Weiner wrote:
David Damerell wrote: However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. The crankset may have been designed with wider, 5/6 speed chain in mind, where the rivets stick out more. Many chainrings are asymmetric - perhaps the 42 can be turned around Curiously, I noticed this after posting; for now I've flipped the 42. I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. Ingenious - but do they help with upshifts? The derailleur cage doesn't provide much upwards hoik, because it has to do most of its work for the 28-42 shifts. -- David Damerell Kill the tomato! |
#7
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Shifting problems on Stronglight 86mm BCD cranks
Benjamin Weiner wrote:
David Damerell wrote: However, the chain falls down the gap between the 52t and 42t chainrings, which is a nuisance. The crankset may have been designed with wider, 5/6 speed chain in mind, where the rivets stick out more. Many chainrings are asymmetric - perhaps the 42 can be turned around Curiously, I noticed this after posting; for now I've flipped the 42. I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. Ingenious - but do they help with upshifts? The derailleur cage doesn't provide much upwards hoik, because it has to do most of its work for the 28-42 shifts. -- David Damerell Kill the tomato! |
#8
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Shifting problems on Stronglight 86mm BCD cranks
David Damerell wrote:
Benjamin Weiner wrote: I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. Ingenious - but do they help with upshifts? The derailleur cage doesn't provide much upwards hoik, because it has to do most of its work for the 28-42 shifts. Yes, slightly. This is on a 52-42-30 with plain rings and an old RSX STI triple front lever with no trim adjustment. If it was a friction front shifter, the plain rings would work ok. With the STI, there is a limited range of adjustment where upshifts work, the der can push the chain down to the granny, and chain rub is tolerable. The pins improve front upshifting enough to widen this workable range. Late model Shimano rings also have some shorter teeth to help the downshifting - I've been tempted to file down a couple of teeth to imitate that. Front STI is hardly ideal, but front shifting can be clumsy even with a friction shifter, especially under load. I know, it's "better" not to shift the front under load but if you have hills it's sometimes unavoidable. The mutated chainrings seem to help with that. WRT the derailleur cage and upshifts, sometimes rotating the FD about the seattube slightly helps with that. Triple fronts can be a battle between quicker shifting and tolerable chain rub. I'd like to see the manufacturers improve front shifting before adding more rear cogs, but given the degrees of freedom in any crankset/FD combination, that may be quite hard. |
#9
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Shifting problems on Stronglight 86mm BCD cranks
David Damerell wrote:
Benjamin Weiner wrote: I "pinned" a 52 in an attempt to mimic the Shimano pins that assist 42-52 upshifts. I tapped small holes in the chainring a bit below the teeth, and inserted short M5 setscrews that poke inside by 1-2mm, just enough so the chain doesn't hit them when it's on the 42. If you do this I think the setscrews will push the chain inside enough to land on the 42 when downshifting. Ingenious - but do they help with upshifts? The derailleur cage doesn't provide much upwards hoik, because it has to do most of its work for the 28-42 shifts. Yes, slightly. This is on a 52-42-30 with plain rings and an old RSX STI triple front lever with no trim adjustment. If it was a friction front shifter, the plain rings would work ok. With the STI, there is a limited range of adjustment where upshifts work, the der can push the chain down to the granny, and chain rub is tolerable. The pins improve front upshifting enough to widen this workable range. Late model Shimano rings also have some shorter teeth to help the downshifting - I've been tempted to file down a couple of teeth to imitate that. Front STI is hardly ideal, but front shifting can be clumsy even with a friction shifter, especially under load. I know, it's "better" not to shift the front under load but if you have hills it's sometimes unavoidable. The mutated chainrings seem to help with that. WRT the derailleur cage and upshifts, sometimes rotating the FD about the seattube slightly helps with that. Triple fronts can be a battle between quicker shifting and tolerable chain rub. I'd like to see the manufacturers improve front shifting before adding more rear cogs, but given the degrees of freedom in any crankset/FD combination, that may be quite hard. |
#10
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Shifting problems on Stronglight 86mm BCD cranks
Benjamin Weiner wrote:
[discussion of shifting problems on 52/42/28 Stronglight cranks] WRT the derailleur cage and upshifts, sometimes rotating the FD about the seattube slightly helps with that. Triple fronts can be a battle between quicker shifting and tolerable chain rub. That (rotation) might be an idea. Chain rub is not so great an issue, because the chainstays are quite long, presumably in order to bash the stoker about a bit less over the bumps. -- David Damerell Distortion Field! |
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