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figuring out BB spindle length

Old 03-03-10, 02:37 AM
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pwdeegan
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figuring out BB spindle length

so right now i have a PW 108mm symmetrical BB, but the lateness of the hour makes my head dizzy at math. For my new "ideal" chain line i'll need to add +9mm to the drive side (the left/non-drive side, i figure, can be symmetrical or asymmetrical, i don't care)---currently the chain line is 45mm, and i'll want a 54mm. however, in order to get a BB spindle of proper length for the +9, would i get:
1) a 117mm BB?
2) add +18mm (+9mm for each side) and get a 126mm BB? (That seems ridiculously long/wrong.)
3) get some kind of R+5, and take into account the 5mm (2.5mm could be added to the drive side at the present 45mm chain line measurement) of additional lateral movement in the cups (which would equal what)? A 116mm R+5? A 123 sym?
4) find some other length at complete random? (pick a number, any number)
5) or just ignore the problem, because 9mm of chain flex may not be ideal, but it won't make the Middle East crises any worse.

And yes, i want to keep it JIS square taper; and no, using loctite doesn't frighten me.
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Old 03-03-10, 08:20 AM
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First off, PW makes up to 145mm BB's. 125, 127 and 130mm are all quite common for various cranks.
Second, you don't have to have symmetrical cranks. 2-4mm offset has never been a issue for myself.

Are you sure you need a 54mm chainline?
It may help to be more specific as to your equipment.

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Old 03-03-10, 09:07 AM
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pwdeegan, I would just get a 117mm BB, and shift the spindle to the right the proper amount. You can do it with a couple of the home installation tools, a washer, and a long crank bolt right in the bike, or in various other ways.

Disclaimer: This isn't recommended by Phil Wood, it is recommended by me.
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Old 03-03-10, 10:13 AM
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Originally Posted by helicomatic View Post
pwdeegan, I would just get a 117mm BB, and shift the spindle to the right the proper amount. You can do it with a couple of the home installation tools, a washer, and a long crank bolt right in the bike, or in various other ways.

Disclaimer: This isn't recommended by Phil Wood, it is recommended by me.
I'm not sure you're going to get the effective chainline with a 117mm bb, even with the allowable adjustment which will be about 5mm max to the right. And that's really pushing it. What takes a 54mm chainline? Is that an error?
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Old 03-03-10, 10:26 AM
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operator, I'm suggesting shifting the spindle in the cartridge, not using the cups to shift the cartridge in the frame. Sounds dubious, because it probably is. Has worked for me in the past. It's the only difference between a sym and R+5 phil anyway.

It's the Rohloff that uses a 54mm chainline.
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Old 03-03-10, 12:34 PM
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Originally Posted by helicomatic View Post
It's the Rohloff that uses a 54mm chainline.
yup, retrofit Rohloff install apparently requires a 54mm CL.
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Old 03-03-10, 12:51 PM
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Not knowing the exact equipment, here are some thoughts:
1) If the chainring is mounted on the inside of the spider, can it be moved to the outside?
2) Can you respace the axle and redish the wheel to bring the ideal chainline a little closer?
3) What is causing you to need this chain so far out?
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Old 03-03-10, 04:44 PM
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Originally Posted by urbanknight View Post
Not knowing the exact equipment, here are some thoughts:
1) If the chainring is mounted on the inside of the spider, can it be moved to the outside?
2) Can you respace the axle and redish the wheel to bring the ideal chainline a little closer?
3) What is causing you to need this chain so far out?
good questions; let me clarify.
1) the chainring is already on the outside (and currently with a chainline at 45mm); it's a Sugino single, and i like it and intend to keep it.
2) no; Rohloff internals are off-limits to me and other commoners; only access for Rohloff experts, and maybe wrist-watch repair people. Three internal planetary gears, many little little internal parts; things that when generally left untouched (save for oil renewal) never go bad. ain't broke? don't fix.
3) it's for a Rohloff hub drivetrain. but apparently, many a MTB triple outside-most chainring also runs at 54mm (not necessarily that the corresponding BB must meet that length), according to Rohloff, Sheldon, Thorn, et al.

I guess it's not a big deal then, to have a 123mm BB. I'm just so used to my 1x9 and its relatively close-in chainline that it seemed big. i might just get a 120 and use up 2-3mm of PW BB cup flex. as it stands now, my BB cups are asym. by ~1mm anyway, and it rides fine. Anyway, glad to have had my sleepy-head math 2x checked. Thanks all!
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Old 03-03-10, 06:26 PM
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Originally Posted by helicomatic View Post
operator, I'm suggesting shifting the spindle in the cartridge,
I was under the impression that this is not possible. Or am I mistaken? Phil wood adjustable chainline *is* from moving the cups.



Looking at that picture (and the bb in my hand there is no way that is possible to do).
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Old 03-03-10, 06:29 PM
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Originally Posted by pwdeegan View Post
good questions; let me clarify.
1) the chainring is already on the outside (and currently with a chainline at 45mm); it's a Sugino single, and i like it and intend to keep it.
2) no; Rohloff internals are off-limits to me and other commoners; only access for Rohloff experts, and maybe wrist-watch repair people. Three internal planetary gears, many little little internal parts; things that when generally left untouched (save for oil renewal) never go bad. ain't broke? don't fix.
3) it's for a Rohloff hub drivetrain. but apparently, many a MTB triple outside-most chainring also runs at 54mm (not necessarily that the corresponding BB must meet that length), according to Rohloff, Sheldon, Thorn, et al.

I guess it's not a big deal then, to have a 123mm BB. I'm just so used to my 1x9 and its relatively close-in chainline that it seemed big. i might just get a 120 and use up 2-3mm of PW BB cup flex. as it stands now, my BB cups are asym. by ~1mm anyway, and it rides fine. Anyway, glad to have had my sleepy-head math 2x checked. Thanks all!
Shimano still makes a 127mm bb square taper - $20-$25 MSRP. This is 0.5mm off from being *correct* chainline wise.
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Old 03-04-10, 09:42 AM
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Originally Posted by operator View Post
I was under the impression that this is not possible. Or am I mistaken? Phil wood adjustable chainline *is* from moving the cups.
The spindle is the correct press fit diameter the full length, no nonsense shoulders or circlips:



There's an additional small press fit spacer of sorts inside the cartridge that I assume is meant to help keep the spindle from shifting. Since the spacer isn't the full length between bearings, the cartridge itself is what keeps the bearings properly spaced.

Again, not recommended by Phil Wood etc. etc.
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