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#1
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Rear Derailer Alignment
On a modern road frame, with vertical dropouts, the real derailer mount is such as the centerline of the top derailer guide pulley is located slightly forward of the cassette center line and the Shimano instructions say to adjust the derailer so that the guide pulley is as close as possible, but not touching, the cassette cogs. On an older frame, with forward facing dropouts, the derailer mount is actually forward of the axle by a substantial amount (assuming that the wheel is mounted at the rear of the "dropout" slot) so that if the guide pulley is moved as closely as possible to the pulley will be in front of the cassette cog to the extent that the chain, when exiting the cod will actually be angled upward over the guide pulley which will be slightly forward of a 25 tooth cog. At present I have my rear derailer (Shimano 105), on the older bike, set so that the derailer body is horizontal and disregarded the vertical alignment of the guide pulley with the cassette. Should I attempt to follow the modern Shimano instructions to get the upper guide pulley as close as possible to the cassette cog and disregard the angle of the chain/cassette vertical alignment? -- cheers, John B. |
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#2
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Rear Derailer Alignment
On 12/25/2016 9:10 PM, John B. wrote:
On a modern road frame, with vertical dropouts, the real derailer mount is such as the centerline of the top derailer guide pulley is located slightly forward of the cassette center line and the Shimano instructions say to adjust the derailer so that the guide pulley is as close as possible, but not touching, the cassette cogs. On an older frame, with forward facing dropouts, the derailer mount is actually forward of the axle by a substantial amount (assuming that the wheel is mounted at the rear of the "dropout" slot) so that if the guide pulley is moved as closely as possible to the pulley will be in front of the cassette cog to the extent that the chain, when exiting the cod will actually be angled upward over the guide pulley which will be slightly forward of a 25 tooth cog. At present I have my rear derailer (Shimano 105), on the older bike, set so that the derailer body is horizontal and disregarded the vertical alignment of the guide pulley with the cassette. Should I attempt to follow the modern Shimano instructions to get the upper guide pulley as close as possible to the cassette cog and disregard the angle of the chain/cassette vertical alignment? There's a continuum of performance (not yes/no) and you're right to check that. Try to get as close to these suggested dimensions as possible for optimum shift response: http://www.yellowjersey.org/sisend.html Even moving the axle in relation to the changer pivot can make a big difference. -- Andrew Muzi www.yellowjersey.org/ Open every day since 1 April, 1971 |
#3
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Rear Derailer Alignment
On Mon, 26 Dec 2016 08:40:12 -0600, AMuzi wrote:
On 12/25/2016 9:10 PM, John B. wrote: On a modern road frame, with vertical dropouts, the real derailer mount is such as the centerline of the top derailer guide pulley is located slightly forward of the cassette center line and the Shimano instructions say to adjust the derailer so that the guide pulley is as close as possible, but not touching, the cassette cogs. On an older frame, with forward facing dropouts, the derailer mount is actually forward of the axle by a substantial amount (assuming that the wheel is mounted at the rear of the "dropout" slot) so that if the guide pulley is moved as closely as possible to the pulley will be in front of the cassette cog to the extent that the chain, when exiting the cod will actually be angled upward over the guide pulley which will be slightly forward of a 25 tooth cog. At present I have my rear derailer (Shimano 105), on the older bike, set so that the derailer body is horizontal and disregarded the vertical alignment of the guide pulley with the cassette. Should I attempt to follow the modern Shimano instructions to get the upper guide pulley as close as possible to the cassette cog and disregard the angle of the chain/cassette vertical alignment? There's a continuum of performance (not yes/no) and you're right to check that. Try to get as close to these suggested dimensions as possible for optimum shift response: http://www.yellowjersey.org/sisend.html Even moving the axle in relation to the changer pivot can make a big difference. Thanks for the answer. I had originally thought of removing the existing rear drop outs and replacing them with the more modern vertical drop outs but the bike went together and worked with the originals. Now, of course, with the bike finished I have the time to sit here and speculate on what might have been :-) As this is a "Bangkok Bike" and is ridden in flat terrain with minimal shifting I shall probably end up leaving it as original built :-) -- cheers, John B. |
#4
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Rear Derailer Alignment
JB was wondering abt getting chin on cogs ..... if not using small cog move pulley inboard for a better chainline run.
eyeball the system with string n shims on tubing ..... like blockwork |
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