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Quick question about chainline and bottom bracket length

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Quick question about chainline and bottom bracket length

Old 08-28-21, 02:45 PM
  #26  
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Originally Posted by icemilkcoffee
The 126 or 130 OLD rear hub, has nothing to do with the chainline.
Why not? Wouldn't a bike with a larger OLD generally have a chain line further away from the centerline of the bike?
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Old 08-28-21, 02:49 PM
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Originally Posted by SoSmellyAir
I see; so nothing to do with using the cranks as double or triple.
The OP specificallly said " my intention is to use it as a triple", so I did not want to bring in that complication.

But if you intend to use this triple crankset as a double, then you can use a significantly shorter spindle.
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Old 08-28-21, 03:24 PM
  #28  
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Originally Posted by icemilkcoffee
The OP specificallly said " my intention is to use it as a triple", so I did not want to bring in that complication.

But if you intend to use this triple crankset as a double, then you can use a significantly shorter spindle.
Got it. The OP is not doing this, but I am effectively doing something very similar, i.e., using this crankset for a 1X front setup with the chain ring mounted on the outermost position.
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Old 08-28-21, 03:29 PM
  #29  
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Originally Posted by SoSmellyAir
Why not? Wouldn't a bike with a larger OLD generally have a chain line further away from the centerline of the bike?
Not if you are going from a 126mm 7 speed freehub body to a 130mm 8-10 speed freehub body.

It can be difficult to visualize, but even though all of that additional 4mm width is coming from a wider freehub body only 2mm is further out on the DS. The other 2mm is pushing the hub toward the NDS which results in no change in chainline, center of the freehub body, due to the wider dropouts. The wheel has to be re-dished to compensate for this movement.

Think about the perspective from the DS dropout.

John

Edit Added: This is also why there is a change in chainline going to 135mm using the “same” freehub.
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Old 08-28-21, 07:02 PM
  #30  
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Originally Posted by 70sSanO
Not if you are going from a 126mm 7 speed freehub body to a 130mm 8-10 speed freehub body.

It can be difficult to visualize, but even though all of that additional 4mm width is coming from a wider freehub body only 2mm is further out on the DS. The other 2mm is pushing the hub toward the NDS which results in no change in chainline, center of the freehub body, due to the wider dropouts. The wheel has to be re-dished to compensate for this movement.

Think about the perspective from the DS dropout.

John

Edit Added: This is also why there is a change in chainline going to 135mm using the “same” freehub.
So the center of the cassette (regardless of the number of cogs) stay at the same position relative to the centerline of the bike regardless of whether the OLD is 126 mm, 130 mm, or 135 mm? But OLD 130 mm road bikes generally have a 45 mm chain line, while OLD 136 mm hybrids (at least the inexpensive ones using the previously ubiquitous Tourney triple crankset) have a 47.5 mm chain line.
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Old 08-28-21, 07:09 PM
  #31  
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Originally Posted by Piff
Thank you for offering to tell me how your experimentation goes, greatly appreciated
Update here: Bike Forums - View Single Post - Converting Trek FX2 to 1x

Summary: I ordered a Tange Seiki LN-3922 (made in Japan!) bottom bracket with a spindle length of 107 mm to replace the cheap stock VP bottom bracket with a 121.5 mm spindle length in order to (theoretically) move the crank arm and chain ring 7.25 mm inward.

Tange LN-3922 Bottom Bracket | - Ben's Cycle (benscycle.com)

The same bottom bracket is also available with a 115.5 spindle length, so hope one of the two works out for Piff .
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Old 08-28-21, 07:49 PM
  #32  
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Originally Posted by SoSmellyAir
So the center of the cassette (regardless of the number of cogs) stay at the same position relative to the centerline of the bike regardless of whether the OLD is 126 mm, 130 mm, or 135 mm? But OLD 130 mm road bikes generally have a 45 mm chain line, while OLD 136 mm hybrids (at least the inexpensive ones using the previously ubiquitous Tourney triple crankset) have a 47.5 mm chain line.
The quick answer is 126 (7) to 130 (8-10) the increase is all in the freehub body equally divided between DS and NDS.

130 (8-10) to 135 (8-10) basically just moves the same freehub out 2.5mm. I believe it was to add chainstay clearance.

Note: There are some 7 speed on 130 and 135 that push the centerline out. And I’ve also seen some freehub bodies that are set a little bit farther from the dropout.

John
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Old 08-29-21, 04:07 PM
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Originally Posted by icemilkcoffee
The 126 or 130 OLD rear hub, has nothing to do with the chainline.
Originally Posted by SoSmellyAir
Why not? Wouldn't a bike with a larger OLD generally have a chain line further away from the centerline of the bike?
Only at the extreme ends of the cluster, and trying to accommodate the extreme at one side of the cluster would worsen it for the other side. That's why chainline is measured from the centerline of the chainrings to the centerline of the cluster:
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Old 08-29-21, 10:26 PM
  #34  
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Thanks everyone for all the help, I went ahead and purchased a 113mm spindle as well as the cranks. I'll report back once they arrive and are installed!
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Old 08-30-21, 01:21 PM
  #35  
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Originally Posted by Piff
Thanks everyone for all the help, I went ahead and purchased a 113mm spindle as well as the cranks. I'll report back once they arrive and are installed!
Which bottom bracket did you end up ordering? Shimano BB-UN300?
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Old 08-30-21, 08:16 PM
  #36  
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Originally Posted by SoSmellyAir
Which bottom bracket did you end up ordering? Shimano BB-UN300?
Actually, just a cheap spindle. This one here.
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Old 08-30-21, 08:19 PM
  #37  
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Originally Posted by Piff
Actually, just a cheap spindle. This one here.
Oh, I see; you did buy only a spindle. You must have a serviceable bottom bracket.
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Old 09-02-21, 07:41 PM
  #38  
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Piff Achtung! Note of caution regarding the Dimension Cyclocross crank arms.

110 Crankset | Dimension Bike Products

If the drain drops toward the inside, the 74 BCD mounting nubs make it super difficult to extricate the chain. I learned this during a test ride of my 1X setup before shortening the chain. I have not found a 74 BCD chain guard. Hopefully, shortening the chain reduces the possibility and frequency of dropping the chain.
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Old 09-04-21, 06:08 PM
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Originally Posted by SoSmellyAir
Piff Achtung! Note of caution regarding the Dimension Cyclocross crank arms.

110 Crankset | Dimension Bike Products

If the drain drops toward the inside, the 74 BCD mounting nubs make it super difficult to extricate the chain. I learned this during a test ride of my 1X setup before shortening the chain. I have not found a 74 BCD chain guard. Hopefully, shortening the chain reduces the possibility and frequency of dropping the chain.
Ty for the heads up! It wouldn't look as clean, but perhaps a front derailleur would keep that from happening as well.

As for the chainline....well I actually have decided to put the crank on a different hike, a 1988 Miyata Valley Runner. The chainline works great as a double with a 110mm un55 bottom bracket. But, it has to be said that the 110mm is asymmetrical, the NDS is longer by 3.5mm. The drive side length of the spindle is more equivalent to a symmetrical 107mm un55.
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Old 09-04-21, 06:54 PM
  #40  
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Originally Posted by Piff
Ty for the heads up! It wouldn't look as clean, but perhaps a front derailleur would keep that from happening as well.
A dedicated chain retention mechanism works better and looks cleaner but costs more than a front derailleur!

Gusset Lil Chap chain device, 34.9/31.8mm - Modern Bike

I ordered the $20 Amazon version.
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Old 09-08-21, 08:13 AM
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Originally Posted by Piff
Actually, just a cheap spindle. This one here.
Would you mind giving us your thoughts concerning the quality of the spindle you ordered, as well as a follow-up in regarding same in a few weeks? I'm considering getting one or more of those for future use, and would like to know whether they're worth the $$$. IMO I'm likely not the only one, either.
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