Different types of bottom bracket

Giraffoto
Giraffoto Posts: 2,078
edited January 2012 in Workshop
To what extent is it possible to swap between the various types that are available when changing cranksets? For example (not that I'm thinking of doing this any time soon), if I took the square tapered crankset off my road bike or the Octalink one off the MTB and decided to replace it and the BB with one of the newer varieties with external bearings, would my front mech still be able to cope with it, and what else (if anything) would be thrown out of line?
Specialized Roubaix Elite 2015
XM-057 rigid 29er

Comments

  • As long as you don't mix and match BBs with incompatible chainsets, you are fairly safe. I run a Campagnolo UT chainset and BB on a Shimano bike without any problem. Your swap is perfectly doable, but I am not sure it's a good idea... Octalink cartridge BB last a lot longer than external bearings... in fact there is no practical advantage in running on external bearings, other than they are easier to service... as we are neighbours, feel free to contact me and I can show you some options
    left the forum March 2023
  • Giraffoto
    Giraffoto Posts: 2,078
    Thanks for that, and for the offer - it's something I've been increasingly curious about when I've read about all the different varieties that are out there. When I started riding there were only two types - square tapered and cottered - and they went in identical, unsealed bearings. Now that there are at least four ways of putting your crankset together, each of which has its own style of bottom bracket I just wondered how interchangeable they all are.
    Specialized Roubaix Elite 2015
    XM-057 rigid 29er
  • Giraffoto wrote:
    Thanks for that, and for the offer - it's something I've been increasingly curious about when I've read about all the different varieties that are out there. When I started riding there were only two types - square tapered and cottered - and they went in identical, unsealed bearings. Now that there are at least four ways of putting your crankset together, each of which has its own style of bottom bracket I just wondered how interchangeable they all are.

    They are not. The most used standard is Hollowtech 2, which is compatible between Shimano, SRAM, FSA and others. Campagnolo has its own systems (UT and PT)... these are all external bearing systems, easy to service, but very short bearing lifetime, compared to square taper or splined cartridge systems... then more recently BB 30 and press fit BBs came into play for non threaded carbon shells, yet another standard. In a way it's good that so many new products become available, on the other hand compatibility is more and more tricky
    left the forum March 2023
  • Giraffoto
    Giraffoto Posts: 2,078
    ... these are all external bearing systems, easy to service, but very short bearing lifetime, compared to square taper or splined cartridge systems...

    That's rather surprising. I mean, completely believable now I come to think about it, when I see the amount of muck that gets caked on the BB, but still rather surprising that they come with such a disadvantage. That being the case, what advantages do the external bearings have?
    Specialized Roubaix Elite 2015
    XM-057 rigid 29er
  • nicklouse
    nicklouse Posts: 50,673
    short life is normally due to poor BB shell preperation. But is still way shorter than the old internal BBs.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • Giraffoto wrote:
    ... these are all external bearing systems, easy to service, but very short bearing lifetime, compared to square taper or splined cartridge systems...

    That's rather surprising. I mean, completely believable now I come to think about it, when I see the amount of muck that gets caked on the BB, but still rather surprising that they come with such a disadvantage. That being the case, what advantages do the external bearings have?

    At our level, no advantage. You have to ask someone who race at a certain level if he has noticed improvements since the days of the square tapers... but as I said in another thread, Eddie Merckx won the Milan Sanremo in 1967 at a higher average speed than Goss last year, or Cavendish before, so I don't see all these improvements in bicycle engineering making a difference in practice.
    left the forum March 2023
  • I agree it would be unlikely a normal rider would notice any difference (I certainly never would!) but just for my education - Were external BBs not designed to allow a larger diameter axle, which is stiffer and hence more efficient power transfer from body to drivetrain?
  • Sorry I should also have said - Are external BBs not supposed to allow larger bearings (as they don't have to be contained in the shell) and so are suppossed to be more durable?

    Is it all BS then re the adtvantages of Ext BBs?
  • ChrisSA
    ChrisSA Posts: 455
    They are not. The most used standard is Hollowtech 2, which is compatible between Shimano, SRAM, FSA and others.

    SRAM GXP is not compatible with HTII/FSA.
  • External BBs have more drag than old square taper BBs as well as a shorter life.
    The thicker axle should be stiffer and the wider spaced bearings should support the axle better, which is the only real advantage, appart from easy assembly on the production line.
    Bike tests and crank tests spend a lot of time banging on about 'measured' stiffness or deflection. Riders can then compare the numbers and make judgements based on them. Manufacturers spend time trying to make their cranks the stiffest. I am 92 kg and ride a fixie with a set of old TA cranks. I have never noticed the cranks flexing, even compared to my more modern bikes.
    Perhaps all these different systems are fixing a problem that doesn't really exist. But we are all addicted to a bit of tech and bling.
  • Giraffoto
    Giraffoto Posts: 2,078
    External BBs have more drag than old square taper BBs
    That gets me onto another thing I've noticed - does a freehub have intrinsically more bearing drag than an old-fashioned freewheel, or has mine just got lots of thick grease in it? I noticed when I had my new MTB hanging up for a thorough clean that the drag of the freehub is enough to push the chain quite slack at the top, something I've not noticed with freewheels.
    Perhaps all these different systems are fixing a problem that doesn't really exist. But we are all addicted to a bit of tech and bling.
    That sounds familiar - don't you wish they'd pick one way to "fix" it and stick to though?
    Specialized Roubaix Elite 2015
    XM-057 rigid 29er
  • Giraffoto wrote:
    External BBs have more drag than old square taper BBs
    That gets me onto another thing I've noticed - does a freehub have intrinsically more bearing drag than an old-fashioned freewheel, or has mine just got lots of thick grease in it? I noticed when I had my new MTB hanging up for a thorough clean that the drag of the freehub is enough to push the chain quite slack at the top, something I've not noticed with freewheels.
    Perhaps all these different systems are fixing a problem that doesn't really exist. But we are all addicted to a bit of tech and bling.
    That sounds familiar - don't you wish they'd pick one way to "fix" it and stick to though?

    Old freewheels did spin better, but the difference in terms of wasted kinetic energy is negligible. The pawls only work when you are not pedalling and old bikes do not freewheel much better than modern ones. It's due to different design of the pawls, which have now fewer but stronger springs. Old freewheels were significantly heavier than modern freehubs + cassette. I have to say they were also less durable than modern freehubs are
    left the forum March 2023