Replace GXP BB with Hollowtech

dilatory
dilatory Posts: 565
edited October 2014 in Workshop
Is it possible to straight up replace GXP BB with something else? It's oddly expensive for BB and Crankset replacement. It seems like I could just unscrew GXP and screw in HT but probably there's some odd interface just to balls it up for me...

Alternatively would HT Crankset work with GXP BB?

Comments

  • jimothy78
    jimothy78 Posts: 1,407
    The axle standards are different, so you can't just replace the crankset.

    However, you are right that you could change the whole setup by simply unscrewing the GXP cups and replacing with HT2. This is assuming you have standard "English" threaded BB shell, of course.
  • dilatory
    dilatory Posts: 565
    Ah well, replacing the BB would be fine, as HT2 is cheaper too! Thanks!
  • jimothy78
    jimothy78 Posts: 1,407
    Be aware that if you buy new, Hollowtech2 chainsets normally come with BB cups included, so no need to purchase separately.
  • Ouija
    Ouija Posts: 1,386
    edited October 2014
    GXP axles are 24mm drive side and 22mm NDS whereas HTII are 24mm both sides. You can use HTII bottom brackets on GXP cranks but you need to buy reducer caps for the non drive side. These press into the NDS cup from either side and meet in the middle of the bearing. Essentially reducing the inside diameter of the bearing from 24mm to 22mm, so the GXP axle fits snugly on that side (also prevents you over tightening the crank arms and stressing the bearings).

    Some aftermarket HTII bottom brackets come with the reducer cups (Trailbright, springs to mind) or offer the option of including them for a few quid extra. Hope also do them.
  • arlowood
    arlowood Posts: 2,561
    jimothy78 wrote:
    Be aware that if you buy new, Hollowtech2 chainsets normally come with BB cups included, so no need to purchase separately.


    News to me!!!

    I've purchased 2 new 105 5700 chainsets in the last year and also a Shimano CX50 chainset 2 weeks ago and none of these was supplied with BB cups included.

    HTII BB's are cheap enough anyway so I would err on the side of caution and buy one separately - don't assume that the cups will come with the chainset.
  • heez29
    heez29 Posts: 612
    HT2 chainsets come with BBs only with MTB chainsets. Road ones don't.
  • dilatory
    dilatory Posts: 565
    heez29 wrote:
    HT2 chainsets come with BBs only with MTB chainsets. Road ones don't.

    Oh really? I'm thinking of putting a Deore crankset on and running a narrow/wide single ring up front (for a CX project). Might be worth looking around then, if I can get a bargain new one it'll probably cost the same as second hand + BB.
  • Ouija
    Ouija Posts: 1,386
    heez29 wrote:
    HT2 chainsets come with BBs only with MTB chainsets. Road ones don't.

    Largely because there isn't the plethora of BB standards on mountain bikes as there is on road bikes so Shimano can be reasonably sure that if they include a 24mm HTII BB with the cranks they will probably fit the bike. There seems to be a bewildering number of BB variations on road bikes that will take a 24m HTII axle but not a HTII BB itself, so i guess they decided to leave the BB out and leave it up to the buyer to get the correct BB for their frame.

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