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I am planning to upgrade a few of my bikes .. some due to faulty BBs and some just to upgrade the crankset. Here are the questions I have:

1) Road vs MTB

I read from the another post about Road vs MTB Hollowtech that the BB and Cranksets gotta be the same category.

  • What about other types of BBs like square tapered/Octalink?
  • Is it universal for both MTB and Road?

2) BB spindle width and crankset compatibility

Was browsing some online stores for cranksets, and saw a few that mention that the particular crankset is compatible with spindle width 103-113.

  • Why is there this spec?
  • What is the difference?

My issue is that 2 of my foldies have BB width of 125 and 127mm ..

  • So what bad things could happen if I used a crankset designed for narrower BBs?
  • Or for the reverse?

3) Tolerance for difference in BB width

  • Assuming I cannot can a BB same as the old one, what is usually a safe tolerance range + or - from the existing?
  • Is it better to get one that's longer or shorter?

4) Changing from square tapered to hollowtech

  • Hollowtech BBs don't have a spindle width specified. What do I need check if I am converting from square to hollow?
  • Can I convert my foldies to hollowtech? Given their BB is at the wider end of 125mm?

5) Changing from square tapered to Octalink

  • what is the width that I'll need to add or subtract if I want to convert from square to Octalink?

6) Changing from to Truvativ's Powerspline to Octalink or Hollowtech

I've got a road bike from 2006/7 that is using Powerspline .. which is a dying/dead product so am thinking of converting.

  • what is the width that I'll need to add or subtract if I want to convert from square to Octalink?

7) Adjustments for change in Chainring/Rear Cog

Do I need to change BB with a different spindle width if:

  • Change the crankset between 1/2/3 chainring?

  • Change the rear from a 6sp to a 9sp? Thought I remember that I'll change different hub size if I want to change to a cassette of different speed.

8) Ceramic Ball bearings

  • I've seen some BBs using ceramic bearings. What are the advantage of ceramics?
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    I am voting to close this as too broad. It would be much better asked as a number of separate questions, many which have already been asked on this site. – mattnz Oct 30 '19 at 20:21
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That's a lot of questions but I think I can answer most of them with a couple of answers.

With respect to cartridge bottom brackets and cranks (Square taper, Octalink etc.):

  1. The cartridge need to be appropriate for the frame bottom bracket shell width (traditionally 68mm for road bike and 73mm for mountain)
  2. The axle length need to be correct for the specific crank you are using to get the correct chain line. It's critical to know that different model cranks need different length axles to get the same chainline, so you need to look up the specifications for the crank to find out the bottom bracket axle length required.

With respect to Hollowtech II (and other external threaded bearing systems like GXP), things are a bit simpler, because the drive side crank comes with the axle attached. The axle length is just whatever is required for the bottom bracket shell width the crank is designed for. You do have to pick a crank that gives the correct chainline for your frame of course.

With respect to deviation from the correct chainline if you use a different cartridge BB than the crank is designed for, I would not recommend being more than a few millimeters out. If the chainrings are to far inboard you may get interference with the chainstay, too far outboard can result in derailleur reach problems.

If you are using Shimano products you can look up the specifications for cranks, which includes nominal chainline the bottom bracket models that work. Start here: https://productinfo.shimano.com/#/spec.

  • Do you mean 73mm for mountain bikes? – Reid Oct 30 '19 at 23:15
  • @Reid. Yep. Typo fixed – Argenti Apparatus Oct 31 '19 at 0:58
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I'll focus on question 8. The short answer is that they have lower rolling resistance than steel bearings, but the difference is tiny (previous SE answer by R Chung). It is unlikely to be meaningful for amateur cyclists, or even perceptible.

Also, one article interviewed Paul Lew, who has a long background in high performance wheels. He argues that in the industrial applications where ceramic bearings are advantageous, the operating conditions are clean and the bearings aren't run with grease. Running with just a light oil lubricant or no lubricant is not an option for most bicycles. Running them with grease will offset much of the rolling resistance benefit.

Another interviewee raised the issue that ceramic bearings are very hard. As bicycles hit potholes, the impacts will push the ceramic balls into the steel races, potentially damaging them. Thus, that interviewee seemed to feel that this would further limit their practical durability on bikes.

That said, high-quality ceramic bearings should have lower rolling resistance. They're also lighter than steel. If you are building a bike for something like the hour record, then maybe they are something you should consider.

  • Ceramic bearings allow you to go much faster because your wallet is so much lighter :) There is also the placebo effect, after spending that much money, you put in more effort to prove (to yourself as much as anyone else) that the investment was worth it. – mattnz Oct 30 '19 at 20:24
  • Me and a friend once compared our hubs by holding front wheel by the axle after an initial push. My friend's ceramic bearing hub (road bike, I don't remember the brand) kept the wheel spinning way more time than my arm could withstand, my Shimano LX would spin for about two minutes, tops. – Jahaziel Oct 30 '19 at 21:00
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    @Jahaziel That's not a fair comparison. If your friend's rim and tire had more mass, and the starting speed were the same it would keep moving for longer. If you did the same comparison with a good quality new steel bearing and a worn one you'd see a difference. There are also other sources of friction you were not taking account of. – Argenti Apparatus Oct 30 '19 at 21:06
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    @Jahaziel in addition to what Argenti said, consider the Cyclingweekly article I linked (1st link). It says that bearing seals may also impact the equation. Low drag seals will reduce drag no matter what the bearing type, but they won't keep contaminants out. Then if you read the road.cc link (3rd one), CeramicSpeed's own rep says that spinning in the hand is not a sufficient indicator of how the bearing performs on the bike, when it's under load. – Weiwen Ng Oct 30 '19 at 21:16
  • @ArgentiApparatus Indeed they where different wheels. But my friend's where high quality road bike ones, mine where new-ish MTB 26 x 1.5 slick tires on entry level alexrims, my wheels where way heavier than my friend's. My hubs had been recently re-packed, and has not seen too many kilometers the day that test was made. Anyway, I'm well used to the feel of new steel bearing entry and mid level hubs. The difference with the other ones was VERY noticeably (at least on the hand, I doubt actual riding would be significantly different beyond placebo effect). – Jahaziel Oct 30 '19 at 21:20

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