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Power Spline to Square Taper size difference?

Old 06-06-23, 12:38 AM
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Power Spline to Square Taper size difference?

I have an older bike with a Power Spline 68x113 Bottom Bracket and it will be replace with a Square Taper BB

The question is:

Do I use the exact same measurements or do I need to consider a longer or shorter spindle to compensate for the different design?
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Old 06-06-23, 02:35 AM
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I am guessing that the OP is changing his cranks to square taper as well and is concerned about chain line. @CrimsonEclipse I hope I got that right and sorry I don't know the answer to your question but going to follow this thread for knowledge
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Old 06-06-23, 02:50 AM
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Originally Posted by JoeTBM
I am guessing that the OP is changing his cranks to square taper as well and is concerned about chain line. @CrimsonEclipse I hope I got that right and sorry I don't know the answer to your question but going to follow this thread for knowledge
You are correct.

I will be changing the cranks too.
Thus, I was concerned if the spacing for the new cranks and crank arms would be changed considerably.

Thanks Joe!
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Old 06-06-23, 02:50 AM
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Originally Posted by Bill Kapaun
A sq. taper is NOT a spline.
It will not work.
What are you thinking?


I was thinking someone here would be mature.
Move along
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Old 06-06-23, 03:32 AM
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Originally Posted by CrimsonEclipse
I was thinking someone here would be mature.
Move along
Ignore List
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Old 06-06-23, 03:35 AM
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Originally Posted by Bill Kapaun
Ignore List

Oh no!
I'm being ignored by a rude witless troll!
What ever will I do?
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Old 06-06-23, 07:09 AM
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The fact that you have a powerspline now has nothing to do with what BB you'll need for a square taper crank.

You need the right BB for the model crank you are getting and the width of the BB shell in your frame.
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Old 06-06-23, 07:30 AM
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Originally Posted by Kontact
The fact that you have a powerspline now has nothing to do with what BB you'll need for a square taper crank.

You need the right BB for the model crank you are getting and the width of the BB shell in your frame.
This. Pick out your new (square taper) crank and find out what BB it needs, then buy the BB to match. Note some cranks may have a range -- choose the top end for a MTB or stout frame hybrid, and the narrow BB for a road bike.
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Old 06-06-23, 08:28 AM
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Originally Posted by CrimsonEclipse
Oh no!
I'm being ignored by a rude witless troll!
What ever will I do?
Don't worry. Most of us are on that list. It's just what he does. The BF equivalent of covering his ears and yelling, "LA LA LA! I can't HEAR YOU!"
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Old 06-06-23, 09:50 AM
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Originally Posted by pdlamb
This. Pick out your new (square taper) crank and find out what BB it needs, then buy the BB to match. Note some cranks may have a range -- choose the top end for a MTB or stout frame hybrid, and the narrow BB for a road bike.

...this, pretty much. The power spline crank you have (and all such cranks, from what I understand,) are specifically matched to that sort of bottom bracket unit. They actually make it a lot easier to install such a crank, because they all space properly when used with the appropriate power spline sealed unit. The length of that unit's spindle, (which is universal,) has no relationship to what you'll need for your new square taper crank.
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Old 06-06-23, 10:34 AM
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To be fair to Bill Kapaun he does regularly have good advice but a very short temper for B.S. or what he perceives as B.S. he does it to a lot of folks. Could you lighten up Bill, sure will you, probably not but this is the internet and people will do as they do. People have their different and sometimes divergent personalities but that is what makes BF, BF, is the mix of different people and opinions and love and hate of different aspects of cycling.

In terms of the OPs question you will need to get the correct length square taper bottom bracket for your crank which is what it is dependent on. Once the old crank is gone you don't need to worry about any part of it including B.B. as that has zero bearing on your new set up.
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Old 06-07-23, 04:40 AM
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Originally Posted by CrimsonEclipse
I have an older bike with a Power Spline 68x113 Bottom Bracket and it will be replace with a Square Taper BB

The question is:

Do I use the exact same measurements or do I need to consider a longer or shorter spindle to compensate for the different design?
Are you asking about maintaining the chainline?
If so, you need to measure the chainline with powerspline BB and replace with appropriate combination of square taper crank and square taper BB.
You should choose the crank first and then select BB axle length based on required chainline.
Experts, feel free to chime in.
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Old 06-07-23, 07:15 AM
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Originally Posted by anga
Are you asking about maintaining the chainline?
If so, you need to measure the chainline with powerspline BB and replace with appropriate combination of square taper crank and square taper BB.
You should choose the crank first and then select BB axle length based on required chainline.
Experts, feel free to chime in.
There is no standardized industry method for selecting BBs to match a chainline. That's why we have standardized chainlines, largely dictated by BB shell width. If the OP buys the correct BB, as recommended by the crank's manufacturer, for the frame's specifications, the chainline will be correct.
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Old 06-07-23, 08:07 AM
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Originally Posted by Kontact
There is no standardized industry method for selecting BBs to match a chainline. That's why we have standardized chainlines, largely dictated by BB shell width. If the OP buys the correct BB, as recommended by the crank's manufacturer, for the frame's specifications, the chainline will be correct.
From
https://bike.shimano.com/en-EU/produ.../FC-RS200.html

Chain line (mm) 43.5
Recommended bottom bracket|Threaded (normal) BB-UN300Axle length of BB-UN/ES (mm)|Threaded (normal) MM110

Choosing a manufacturer recommended 110mm BB gives a 43.5mm chainline. If one wants a 47mm chainline, does one have to look for a crankset with 47mm chainline or choose a BB with 117mm axle?
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Old 06-07-23, 07:36 PM
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Originally Posted by anga
Are you asking about maintaining the chainline?
If so, you need to measure the chainline with powerspline BB and replace with appropriate combination of square taper crank and square taper BB.
You should choose the crank first and then select BB axle length based on required chainline.
Experts, feel free to chime in.
Yep!
Didn't expect a simple question to create such drama.

I'll probably just get the same size and simply move the chainring as necessary
(bolts, spacers, position)
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Old 06-07-23, 08:40 PM
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Originally Posted by anga
From
https://bike.shimano.com/en-EU/produ.../FC-RS200.html

Chain line (mm) 43.5
Recommended bottom bracket|Threaded (normal) BB-UN300Axle length of BB-UN/ES (mm)|Threaded (normal) MM110

Choosing a manufacturer recommended 110mm BB gives a 43.5mm chainline. If one wants a 47mm chainline, does one have to look for a crankset with 47mm chainline or choose a BB with 117mm axle?
Cranks designed for more than one application often have two recommended BBs. If not you would generally add or subtract 2.5mm per side. But you ought to consider why there isn't a recommended BB for that other chainline - often you'll run into a problem with the chainstays or the front derailleur.
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Old 06-07-23, 08:42 PM
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Originally Posted by CrimsonEclipse
Yep!
Didn't expect a simple question to create such drama.

I'll probably just get the same size and simply move the chainring as necessary
(bolts, spacers, position)
Why not buy the crank and BB that works for your application.

Changing chainline with spacers generally doesn't work well.
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Old 06-07-23, 08:47 PM
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Originally Posted by CrimsonEclipse

I'll probably just get the same size and simply move the chainring as necessary
(bolts, spacers, position)
You're changing the crankset, and the new crankset will use a different bottom bracket standard than your previous one (PowerSpline to square taper, in this case). When you choose your new crankset, forget about your old crankset and bottom bracket, and this would be the case even if you were just swapping one square taper crankset for another, . Purchase your new crankset, and purchase the square taper bottom bracket with the spindle length recommended by the manufacturer for that crankset. Even within the "square taper" bb standard, one crankset vs another will very commonly requrire a different spindle length to achieve a good chainline on a given frame. Again, the crankset manufacuture will state recmmended bb spindle length for whatever crank you choose.
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Old 06-07-23, 10:48 PM
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Originally Posted by CrimsonEclipse
Yep!
Didn't expect a simple question to create such drama.

I'll probably just get the same size and simply move the chainring as necessary
(bolts, spacers, position)
That may not preserve the current chainline.
Measure current chainline.
If your preferred crankset gives a chainline close to current one with recommended BB, problem solved. If within 2.5mm, choose a BB with appropriate axle length as suggested by Kontact.
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