It’s crank measuring day
08-29-20, 04:33 PM
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It’s crank measuring day
I bought a 155mm Origin8 crankset for my wife’s bike. I gather the Origin8 crank is a BMX crank. I needed to check if the chain ring spacing is good for double chain rings. So I measured the thickness of the chainring mounting tangs for various Shimano cranks for comparison:
600 FC6400: 3.4mm
RX100 FC A550: 3.5mm
RSX FC A410: 3.8mm
105 FC5700: 3.5mm
Origin8 crankset: 3.7mm
So it seems like 3.4-3.5mm is typical, but for some screwed up reasons the RSX crank is 3.8mm. Why Shimano why? Anyways the Origin8 crank looks to be in the ballpark.
600 FC6400: 3.4mm
RX100 FC A550: 3.5mm
RSX FC A410: 3.8mm
105 FC5700: 3.5mm
Origin8 crankset: 3.7mm
So it seems like 3.4-3.5mm is typical, but for some screwed up reasons the RSX crank is 3.8mm. Why Shimano why? Anyways the Origin8 crank looks to be in the ballpark.
08-29-20, 05:13 PM
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I’m not going to look up all the cranks, but you do realize that Shimano, and other manufacturers, adjusted the chainring spacing to accommodate narrower chains used for a higher number of cassettes cogs.
The reason is that you can’t run a 10 speed chain on a crank designed for a 6 or 7 speed chain. There is a good chance it will float between the chainrings when you shift between rings.
John
The reason is that you can’t run a 10 speed chain on a crank designed for a 6 or 7 speed chain. There is a good chance it will float between the chainrings when you shift between rings.
John
08-29-20, 05:56 PM
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Also, I am mostly in the small ring, so don't shift the front much.
It's not perfect, but quite workable. I wouldn't use it on a race bike.
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Last edited by Homebrew01; 08-29-20 at 06:05 PM.
08-29-20, 06:05 PM
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I’m not going to look up all the cranks, but you do realize that Shimano, and other manufacturers, adjusted the chainring spacing to accommodate narrower chains used for a higher number of cassettes cogs.
The reason is that you can’t run a 10 speed chain on a crank designed for a 6 or 7 speed chain. There is a good chance it will float between the chainrings when you shift between rings.
John
The reason is that you can’t run a 10 speed chain on a crank designed for a 6 or 7 speed chain. There is a good chance it will float between the chainrings when you shift between rings.
John
I had concerns, but I didn't notice a single problem with my 9 speed chain.
It was apparent that 165mm made a wonderful difference vs 170mm, that I immediately ordered a new, cheap triple. So, it was probably less than a week that I ran the cotters. It was a friction shifter, so I have no idea on the indexing.
08-29-20, 06:43 PM
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What does this mean for your swap?
08-29-20, 07:19 PM
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08-29-20, 10:13 PM
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You would think so , but the 5700 (10 speed) has the same spacing as the 6400 (which started out as a 6 or 7 speed group) and RX100 (8 speed), while the RSX (7 speed) is an outlier by itself.
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