Inner chainring too close
04-16-21, 06:26 AM
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Inner chainring too close
Hi all,
I've just replaced my 50T 110PCD 8 speed outer chainring, it all seems fine except for the inner chainring (34T) that now sits too close to the outer chainring and the chain won't sit on the teeth as there's no gap and drops down. Any advice on this matter would be greatly appreciated. Thanks
I've just replaced my 50T 110PCD 8 speed outer chainring, it all seems fine except for the inner chainring (34T) that now sits too close to the outer chainring and the chain won't sit on the teeth as there's no gap and drops down. Any advice on this matter would be greatly appreciated. Thanks
04-16-21, 06:50 AM
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Apparently your new 50T chainring is intended for 9 or 10-speed use and offset inward to narrow the gap required by narrower 9 or 10-speed chains. You will either have to shim the chainring more outboard or fit a narrower chain. BTW, 10-speed chains work fine on 8-speed cassettes.
04-16-21, 07:03 AM
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Check to be sure that you didn’t re-install the inner chainring backwards. If it has an offset and was installed flipped over, you’d have the same problem.
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04-16-21, 07:10 AM
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Apparently your new 50T chainring is intended for 9 or 10-speed use and offset inward to narrow the gap required by narrower 9 or 10-speed chains. You will either have to shim the chainring more outboard or fit a narrower chain. BTW, 10-speed chains work fine on 8-speed cassettes.
04-16-21, 07:51 AM
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Thanks for your quick reply. The new chainring specifically says 8 speed. The inner ring (stock) is that tight and close to the outer that I don't think any size chain would manage to sit on it. I've also made sure both chainrings are fitted the correct way round. Any idea what else it could be?
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04-16-21, 08:03 AM
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If you look at the two 50T rings what is different. Specifically the differences of thickness of the rings and where along this thickness are the teeth placed. Some rings have the teeth closer to the side/face that contacts the crank arm spider tab surface and some have the teeth placed more outboard. Also there's the aspect of any inner face ramping or lift pins that can require more space to exist and still let the chain engage the small ring without interference.
The best first choice when replacing rings is to do so with the same as the original. next best is with one that most closely mimics the contours and dimensions of the old. After this one falls back on shimming and likely readjusting the ft der, knowing that some chain rub is likely to be resent as the OEM spec of ring to ring spacing (as the teeth are located WRT to each other) is now different from what the der/shifter combo was intended to work best with.
Shims (they look like thin washers) are available to place between the large ring and the arm tab, or between the small ring and it's side of the tab, depending on how much small ring to chainstay clearance is available. .6mm and 1.2mm thick shims are the usual options. better service focused shops try to keep these on hand jut for this get out of a jam need. Andy
The best first choice when replacing rings is to do so with the same as the original. next best is with one that most closely mimics the contours and dimensions of the old. After this one falls back on shimming and likely readjusting the ft der, knowing that some chain rub is likely to be resent as the OEM spec of ring to ring spacing (as the teeth are located WRT to each other) is now different from what the der/shifter combo was intended to work best with.
Shims (they look like thin washers) are available to place between the large ring and the arm tab, or between the small ring and it's side of the tab, depending on how much small ring to chainstay clearance is available. .6mm and 1.2mm thick shims are the usual options. better service focused shops try to keep these on hand jut for this get out of a jam need. Andy
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04-16-21, 08:14 AM
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If you look at the two 50T rings what is different. Specifically the differences of thickness of the rings and where along this thickness are the teeth placed. Some rings have the teeth closer to the side/face that contacts the crank arm spider tab surface and some have the teeth placed more outboard. Also there's the aspect of any inner face ramping or lift pins that can require more space to exist and still let the chain engage the small ring without interference.
The best first choice when replacing rings is to do so with the same as the original. next best is with one that most closely mimics the contours and dimensions of the old. After this one falls back on shimming and likely readjusting the ft der, knowing that some chain rub is likely to be resent as the OEM spec of ring to ring spacing (as the teeth are located WRT to each other) is now different from what the der/shifter combo was intended to work best with.
Shims (they look like thin washers) are available to place between the large ring and the arm tab, or between the small ring and it's side of the tab, depending on how much small ring to chainstay clearance is available. .6mm and 1.2mm thick shims are the usual options. better service focused shops try to keep these on hand jut for this get out of a jam need. Andy
The best first choice when replacing rings is to do so with the same as the original. next best is with one that most closely mimics the contours and dimensions of the old. After this one falls back on shimming and likely readjusting the ft der, knowing that some chain rub is likely to be resent as the OEM spec of ring to ring spacing (as the teeth are located WRT to each other) is now different from what the der/shifter combo was intended to work best with.
Shims (they look like thin washers) are available to place between the large ring and the arm tab, or between the small ring and it's side of the tab, depending on how much small ring to chainstay clearance is available. .6mm and 1.2mm thick shims are the usual options. better service focused shops try to keep these on hand jut for this get out of a jam need. Andy
04-16-21, 12:06 PM
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If you make some measurements of the spacing with the old and new rings you will able to make an intelligent decision on what thickness of shim/spacer you need. As Andrew Stewart mentioned they are available in 0.6mm increments
04-16-21, 12:09 PM
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I'll get measuring now, thanks for sharing your knowledge
