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Bottom bracket alignment question

BmanBman Posts: 442
Hi, Im busy tring to rehab myself from a hip flexor and groin injury on my right side, so while playing with my cleat setup on my commuting bike (noticed my right heel was too far out on rotation, stressing my ITB), I also got to thinking it felt like my whole right pedal was further away from the centreline than my left. This is a MTB which I built, and looking up the shimano instructions, it says to use 2 spacers on the driveside and 1 on the left, but the centre of my rt pedal is still a full cm further away from the centreline of the bike than the left one.

I know youve got the chainset there on the rt but surely this cant be right and would create an imbalance and certainly not help my injured leg?

Any thoughts would be appreciated.


  • transittransit Posts: 163
    Hmm, that's an interesting question. Not sure about the exact answer but what I do know is that the spacers are there to ensure the chain rings are in line with the cassette to create the correct 'chainline' - this will optimise drive train performance. With that in mind I would imagine the spacers are there to make up for a lack of width of the bottom bracket so whatever bb you use the crankset will be in the same place and thus offset by the same amount.

    That may be a load of rubbish! - but think it makes sense. So, are you measureing the centre line of the bike correctly (note: I have no idea of how that is done!!!), just wondering if you have measured the centre of the bb shell, is the bb shell central in the rest of the frame? Is the BB compatible with the frame?

    Just a few ideas, more questions than answers but thought I'd post as noone else has
  • ZacniciZacnici Posts: 1,385
    Again I am not a bike mech and playing with a BB is just one of things I do not want to touch, but ny understanding is that spacers are to adjust for differeing BB shell widths of 68mm or 73mm. Just a thought but do you have the wrong spacing so that you have spacers for a 68mm install whereas the shell width is actually 73mm?
  • AvoneerAvoneer Posts: 174
    Is this an old type BB or one of the newer external bearing BB30 types?

    As above, generally used to align the front rings with the back, but I agree that it's probably doing nothing for your ITB.

    Merely dropping my saddle 5mm almost completely eliminated my old running ITB issues which I get on the bike on long rides so small misalignments might be problamatic.

    Are you still on an MTB?

    Check that you have adequate clearance from the front rings to chainstay, crank arm to chainstay when it's at 9 o'clock and that your centre front ring kind of points to the middle of the cassette - that'll determine if you can remove a spacer or not.

  • BmanBman Posts: 442
    Thanks for the replies guys, I'll need to check the shell width to make sure its the right one im looking at. The BB is a good old shimano hollowtech 2 so external bearings, and Im measuring from the centre adjustments screw on the SPD pedals to the nearest edge of the downtube (I assumed you should be placed centrally over the midline of the bike). I'll have to check Ive got the right setup for the frame I guess. Think I might measure the other bikes too just to sure.

    I find my MTB with slicks is better for winter/park trail commuting and much better in traffic with narrow gaps, road bike for long rides and summer commuting and tri bike for race days. So i actually think I spend most of my riding time on the MTB, hence the eed to get the setup right.
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