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Y1X498020 Sprocket Wheel 10T B & 12T D
Shimano spare parts and codes can be found here
Y1X498020 Sprocket Wheel 10T B & 12T D
Shimano spare parts and codes can be found here
The strange thing is that there is no noticable wear on the sproket. Put it side to side or back to back against a brand new one and they look the same. (we are not talking about badly worn spiked teeth here, its just that the chain slips but doesn't with a new sprocket) I will try a Shimano dealer but they don't tend to stock 12 speed usually and looking on the Shimano website it isn't a stand alone product. So this is why I was asking if anyone had been able to get one and where from.Order it as a spare part through any authorised Shimano dealer/Service centre
When your smallest sprockets wear past a certain point it stands to reason they will no longer be useable with a new chain. so at that point STOP trying to run new chains on it.
Personally in your situation I'd just ditch 12 speed altogether, fit a more suitable gearing range for the riding you do then let it all wear together instead of swapping/rotating chains. But look after it better. incl always shifting as smoothly as you can (By simply doing this I get 10 to 20 times the mileage you do out of your cassettes)
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