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chainline of Shimano 130 mm road hubs

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chainline of Shimano 130 mm road hubs

Old 02-26-09, 09:39 PM
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chainline of Shimano 130 mm road hubs

For Shimano road cranks, I know that the chainlines for doubles and triples are 43.5 mm and 45 mm respectively. But where is the centerline of the cassette on a road hub? I'm curious where the rings are supposed to be relative to the cassette. Let's say Shimano 130 mm road hubs to be specific. I know that in practice this is probably impossible to predict with that kind of accuracy, but I'd like to know where it should be in theory.
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Old 02-26-09, 11:30 PM
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Theory is practice, practice is theory. Throw a cassette in whatever number you're using on there and measure to the center of center cog, or between center two cogs. BTW, why do you ask?

Add to the mix the fact that MTBs are sometimes set up with chainline favoring the lower gears, while road bikes are sometimes set up with chainline favoring the higher gears.
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Old 02-26-09, 11:55 PM
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Originally Posted by stedalus
But where is the centerline of the cassette on a road hub? I'm curious where the rings are supposed to be relative to the cassette.
The centerline of the cassette is at the #5 cog for a 9-speed cassette and between the #5 and #6 cogs for a 10-speed cassette. Determining the centerline of 8, 7, 6, and 5-speed cassettes is left as an exercise for the student.

It really doesn't make a whole lot of difference with modern chains and cassettes. The chain is often running at such a huge angle that it's incredible it doesn't tie itself in a knot, much less shift accurately and reliably.

Now that you got me curious, I just looked at the first 130mm width hub I came to in my collection. The middle cog is 22mm from the face of the dropout, which means it's 43mm from the center of the hub. Here's the hub:
https://home.comcast.net/~jeff_wills/...es/bike004.htm
Hope that works for you.
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Old 02-27-09, 08:57 AM
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Originally Posted by krems81
Add to the mix the fact that MTBs are sometimes set up with chainline favoring the lower gears, while road bikes are sometimes set up with chainline favoring the higher gears.
This is exactly why I ask. Road cranks have two possible chainlines (43.5 mm and 45 mm) but they use the same hubs. If the cassette is centered at 43.5, then the middle ring on a triple is actually a bit outboard. On the other hand, if it's at 45 mm, then the middle ring is truly in the middle, and on a double, the big ring has a better chainline.

Pretty esoteric question, I know. But a change of pace from the "How do I adjust my FD?" threads, no?



Originally Posted by Jeff Willis
Now that you got me curious, I just looked at the first 130mm width hub I came to in my collection. The middle cog is 22mm from the face of the dropout, which means it's 43mm from the center of the hub. Here's the hub:
https://home.comcast.net/~jeff_wills/...es/bike004.htm
Hope that works for you.
Interesting, thanks.
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Old 02-27-09, 09:05 AM
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Be sure that you understand the 43.5 and 45mm dimensions that you have referred to. The 43.5mm dimension is to a point in space, centered between the rings. Why this is used, I have no idea, since it's stupid to dimension to a point in space. With typical 7.5mm chainring spacing, that makes the tip of a tooth on the big ring 47-48mm from the center line of the ST. That is something you can measure.

The 45mm dimension is normally to the tip of a tooth on the middle ring of a Shimano road triple. FSA cranks are 46mm. The tip of a tooth on the big ring would be another 7.5mm further to the right. A typical MTB cranks has a 50mm chainline.

Last edited by DaveSSS; 02-27-09 at 02:46 PM.
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Old 02-27-09, 11:11 AM
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Originally Posted by DaveSSS
Be sure that you understand the 43.5 and 45mm dimensions that you have referred to. The 43.5mm dimension is to a point in space, centered between the rings. Why this is used, I have no idea, since it's stupid to dimension to a point in space. With typical 7.5mm chainring spacing, that makes the tip of a tooth on the big ring 47-48mm from the center line of the ST. That is something you can measure.

The 45mm dimension is normally to the tip of a tooth on the middle ring of a Shimano road triple. FSA cranks are 46mm. The tip of a tooth on the big ring would be another 7.5mm further to the right.
I've read that it's 5 mm C-C between rings, and that's what I measure on my cranks (one 9 speed, one 10 speed). Admittedly this is with a ruler and some squinting as I don't have calipers here, so maybe I'm off.
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Old 02-27-09, 11:21 AM
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They may use the same hubs but they don't use the same wheels.
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Old 02-27-09, 11:28 AM
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Originally Posted by DMF
They may use the same hubs but they don't use the same wheels.
I don't follow this at all. I see plenty of road bikes that have a double and triple model where the only difference is the crankset and derailleurs, but they use the same wheels. And if they have the same hubs but different rims, the chainline is not going to change.
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Old 02-27-09, 12:07 PM
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I was talking about the difference between road and mountain bikes.

On a road bike the 1.5mm (.06") difference between double and triple cranksets is not particularly relevant. Of more relevance is the way doubles and triples are used. Both rings of a double - especially of a compact double - and the middle ring (but not the outer rings) of a triple are commonly used over the whole cassette range. So while the middle ring might be 1.5mm off the the cassette center plane it is still closer than either double ring (both nominally 2.5mm), making actual maximum chain deflection less with the supposedly mismatched crankset.

The outer rings of a triple are mostly used with the cassette gears at the same end, so in use their chain deflection is also less than that of a double, again making the nominal chainline mismatch irrelevant.

This is one of the two major reasons I prefer a triple to a compact, btw.
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Last edited by DMF; 02-27-09 at 12:15 PM.
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Old 02-27-09, 01:31 PM
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Originally Posted by DMF
I was talking about the difference between road and mountain bikes.
Sure, but they don't use the same hubs.

On a road bike the 1.5mm (.06") difference between double and triple cranksets is not particularly relevant. Of more relevance is the way doubles and triples are used. Both rings of a double - especially of a compact double - and the middle ring (but not the outer rings) of a triple are commonly used over the whole cassette range. So while the middle ring might be 1.5mm off the the cassette center plane it is still closer than either double ring (both nominally 2.5mm), making actual maximum chain deflection less with the supposedly mismatched crankset.
That's if the cassette center is also at 43.5 mm. If it's at 45 mm, then the double big ring has pretty good access to the whole cassette, and the small ring is lined up with the back of the cassette where it mostly gets used anyway (in my experience-- I'm sure other people use different shifting patterns). So, one reason for my original question was to find out if the cassette placement favors the big ring or not.
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Old 02-27-09, 02:45 PM
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Originally Posted by stedalus
I've read that it's 5 mm C-C between rings, and that's what I measure on my cranks (one 9 speed, one 10 speed). Admittedly this is with a ruler and some squinting as I don't have calipers here, so maybe I'm off.
The best way to measure the spacing require the crank to be removed, placed on a flat surface and a measurement taken from that flat surface to the tip of each tooth, then figure the difference. It will be very close to 7.5mm. Sheldon Brown mentions 5mm, but he's wrong. Even the new 11 speed cranks are very close to 7mm, with the big ring moved .6mm closer than before.
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