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Does a crankset upgrade need a bottom bracket upgrade?

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Does a crankset upgrade need a bottom bracket upgrade?

Old 02-16-21, 09:32 PM
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Ataylor
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Does a crankset upgrade need a bottom bracket upgrade?

tl;dr: Should I buy a new one, can I keep my old one (it's nearly 5 years old), or does it depend on if it needs to be changed?

I have a 2016 Specialized Roubaix. I'm interested in upgrading all of my components, which will include the crankset. Should I replace the bottom bracket (BB) as well? What's the conventional wisdom? It seems as though people are all over place on this one. Some guy said he had his for 50 years? While another said that he replaces his every four or five. So do you guys wait until it goes "bad" or is it better to replace it every few years?

The sales rep I spoke to said that it's better to replace it when replacing the crankset for a few reasons:

1) If I use my own (which is a BB30), I'll need an adapter to connect that older bottom bracket with the new crankset (which I believe uses BB60?) and by doing that, over time, more parts can lead to squeaking and rattling issues and what not.

2) I think he said that some of the ball bearings might not sit right or fall out of place or something? Which then would affect the crankset in a negative way somehow? Didn't quite follow what he was saying and there to be honest. Any idea what he was talking about and how often something like that happens? What do you guys think?
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Old 02-16-21, 09:40 PM
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Whether you can keep your old bottom bracket or not depends entirely on the new model crank you choose. Unless it uses the exact same bottom bracket, you may have no choice. I run my bottom brackets until they begin to fail or until I change cranks and have to use a different style. I tend to get many years and many thousands of miles out of a given bottom bracket and usually replace them only because I have fitted an incompatible crank.
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Old 02-16-21, 10:03 PM
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Right, crankset determines bottom bracket, and, to be honest, if you can afford a new crankset, you can afford a new bb. But, one does not HAVE to replace a bb if keeping the same type of crankset. Simple.
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Old 02-16-21, 10:42 PM
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I'm going from a Shimano 105 to an Ultegra R8000 crankset. Would you guys consider those the "same" and thus not necessarily requiring a BB replacement?
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Old 02-16-21, 11:11 PM
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bb

bottom brackets come in different lengths.........103mm ...106mm .....on and on.........your crank requires a specific BB length.......your chain line will be off and it might not shift if you dont use the right length..............not all years of 105s take the same BB length......look up your new crank and see what size of BB is required......only one size will work.....you will need to measure [mic] your old one to se what size it is ........my opinion........A BB upgrade is more important than a crank upgrade.........
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Old 02-17-21, 03:01 AM
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If you're swapping Shimano cranksets you do not need to change anything about your bottom bracket for reasons of compatibility. If the bottom bracket feels absolutely, entirely fine with the crank removed and the bearings turned by hand I'd certainly leave them in. Removing a Shimano crankset is really pretty easy/fast so you're not saving a lot of time long term replacing the BB while you're in there, as it is.

Most modern Shimano cranksets are a standard called Hollowtech II, which is a 24mm steel spindle passing through two bearings and preloaded by tightening the NDS crankarm onto the spindle, which is held by two pinch bolts. The "native" press fit bottom bracket standard for Hollowtech is BB86.5, named after the width of the bottom bracket, whereas BB30 is named after the width of the spindle (30mm), which is confusing. If you have a Shimano crankset in there now you either have an adapter installed into a BB30 bottom bracket, or you have some kind of conversion bottom bracket which typically presses into the BB30 shell and places smaller bearings outside the frame (as BB30 has a narrower shell). The adapters kinda suck and can cause creaking, but most conversion BBs work pretty well.

You're also getting some confusing answers in this thread and elsewhere mistaking modern bottom bracket standards with older, square taper standards. In an old school, cup and cone bottom bracket the actual bottom bracket may never need replacement in its life if its ridden in mostly good conditions and the bearings are replaced and re-greased frequently. More modern sealed cartridge square taper bottom brackets are nonserviceable (aside from replacement) but have often very impressive service life. Most things like Hollowtech II and the various other modern standards often have worse bearing life than these systems.

Bottom bracket life also varies wildly with use conditions, frame alignment, crank spindle tolerance, bearing quality, bearing preload, etc. They need to be replaced when they start feeling bad, whenever that is.
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Old 02-17-21, 01:45 PM
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They are the same. I wouldn't change it on the principle of if it ain't broke don't fix it.
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Old 02-17-21, 02:10 PM
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Originally Posted by homelessjoe View Post
bottom brackets come in different lengths.........103mm ...106mm .....on and on.........your crank requires a specific BB length.......your chain line will be off and it might not shift if you dont use the right length..............not all years of 105s take the same BB length......look up your new crank and see what size of BB is required......only one size will work.....you will need to measure [mic] your old one to se what size it is ........my opinion........A BB upgrade is more important than a crank upgrade.........
Joe,
The OP has external bearing cranksets, the spindle is hollow and fixed permanently to the crank spider...
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Old 02-17-21, 02:37 PM
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parts

Do I have to join the 21 century now....sorry OP for posting antique technology......Ive spent this last year in lockdown rebuilding my fleet of 80s bikes......been working on my chain lines all winter with a box of cartridges and an outside caliper.......generally speaking people should disregard anything I say anyway
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Old 02-17-21, 03:04 PM
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Originally Posted by homelessjoe View Post
bottom brackets come in different lengths.........103mm ...106mm .....on and on.........your crank requires a specific BB length.......your chain line will be off and it might not shift if you dont use the right length..............not all years of 105s take the same BB length......look up your new crank and see what size of BB is required......only one size will work.....you will need to measure [mic] your old one to se what size it is ........my opinion........A BB upgrade is more important than a crank upgrade.........
OT. but please quit the ..... deal is not readable

use line breaks, so people can take advantage of what you are sharing
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Old 02-19-21, 06:50 PM
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Originally Posted by homelessjoe View Post
bottom brackets come in different lengths.........103mm ...106mm .....on and on.........your crank requires a specific BB length.......your chain line will be off and it might not shift if you dont use the right length..............not all years of 105s take the same BB length......look up your new crank and see what size of BB is required......only one size will work.....you will need to measure [mic] your old one to se what size it is ........my opinion........A BB upgrade is more important than a crank upgrade.........
Wrong or right, I appreciate your your intent to help, brother. Thanks for that.

Originally Posted by cpach View Post
If you're swapping Shimano cranksets you do not need to change anything about your bottom bracket for reasons of compatibility...
Gotcha! Thanks a ton for the detailed and very helpful reply. I appreciate it.

Originally Posted by davidad View Post
They are the same. I wouldn't change it on the principle of if it ain't broke don't fix it.
Thanks!
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Old 02-19-21, 09:36 PM
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Originally Posted by homelessjoe View Post
bottom brackets come in different lengths.........103mm ...106mm .....on and on.........your crank requires a specific BB length.......your chain line will be off and it might not shift if you dont use the right length..............not all years of 105s take the same BB length......look up your new crank and see what size of BB is required......only one size will work.....you will need to measure [mic] your old one to se what size it is ........my opinion........A BB upgrade is more important than a crank upgrade.........
OP is clearly not talking about a square taper BB. Otherwise, that would be relevant.

Why all the periods.......who taught you to write in gibberish like that?
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