I need to replace the crankset on my Specialized Rockhopper 29 Expert (year 2017) due to damage. I would prefer not to replace the BB to minimize the cost/effort.

The original crankset is described by Specialized as:

Specialized Stout XC, 2-piece 2x10, 24mm spindle, anti-corrosion hardware``

and the BB as

BSA threaded, external bearing, 73mm width

I have concluded that since most of the drivetrain is SRAM (except of the rear derailleur weirdly), the crankset SRAM GX 1000 GXP would be a suitable replacement since it features 24 mm spindle, has the same 36/22T, the same BCD, setup and looks generally similar on pictures (yeah, I know).

Unfortunately, it fits pretty well, except of one minor detail - the shaft seems a bit too long and there is couple mm wiggle space left when I install the left crank. I have since learned that the BSA threaded is something else than BB30 that the SRAM GX 1000 GXP apparently features, even though they have the same radius. I am very confused by all the different parameters to watch for.

What I want to ask - is there an adapter for this? Or simpler - what should I buy that will fit the BB? Or is this is a lost case and I need a new BB? I do not really feel a need to upgrade the 2x10 setup and just want to fix the bike.

Thanks for help!

Edit: I have found here that the Shimano and Sram Threaded BBs differ. Since my spindle is 24 mm all the way, it is probably compatible with the Shimano system. Would e.g. COMET MODULAR CRANKSET work on my bike better then?

  • It has been almost a year - are you able to provide an update on progress ? – Criggie Apr 12 at 6:40
  • All you need is a Shimano to GXP adaptor. Cheap little C-shaped ring with 22mm ID and 24mm OD. Apparently some FSA cranks’ “24mm” is more like 24.1 or something, and they don’t fit very well at all into Shimano BBs. No idea exactly which models do and don’t fit though. – MaplePanda Apr 12 at 6:56
  • Hi, I ended up buying the FSA Comet Megaexo Modular Crankset 2X. When I first installed it there was a gap as you suggest so I bought a washer and a spacer. However, as I kept constantly tightening the screw the gap slowly disappeared and now the crank is there without any spacer or washer. It does seem weird but I did not touch it for a year and it works fine. I do not feel it squeezes the bearings and neither does it wiggle. Not sure how it was intended to work because the tolerances for that are pretty small. – erkil1452 Apr 13 at 13:57

The parameters involved are as follows:

  1. Your frame’s bottom bracket shell, which is BSA threaded.
  2. The spindle type, which is where you ran into trouble. Shimano specifies a 24mm diameter spindle. SRAM’s GXP is a 24mm spindle that tapers to 22mm on the left crank. I don’t know if there’s a substantive reason for this, or if it’s just to avoid any patents that Shimano had on its Hollowtech II system.

The FSA crank you linked appears to have a 24mm spindle, so this should fit as is. Some companies may make spacers to adapt a Shimano BB to a GXP axle, but I can’t remember who does off the top of my head.

BB30 is a different bottom bracket shell standard entirely. It is one of the press fit BB standards. Many press fit BBs are made to take 30mm axles, but 30mm axles are less common in threaded BBs (but it is possible, and BBs are made for that purpose).

  • Thank you! This confirms what I was thinking. I will try the FSA crank. – erkil1452 Jul 19 '20 at 15:38

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