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?

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

CrimsonEclipse

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!

CrimsonEclipse

I was thinking someone here would be mature.
Move along

Bill Kapaun

Ignore List

CrimsonEclipse

Oh no!
I'm being ignored by a rude witless troll!
What ever will I do?

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.

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.

smd4

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!"

3alarmer 

...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.

veganbikes

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.

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.

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.

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?

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)

Kontact 

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.

Kontact 

Why not buy the crank and BB that works for your application.

Changing chainline with spacers generally doesn't work well.

well biked

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.

anga

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.