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Hi all,
I changed my BB and I am convinced I ordered the correct spindle length for the new part (the old one is long recyled by now) but when the chain is on the large ring of the rear cassette and the large or med ring on the crank, the angle seems soo severe that it drops down to the smalled ring on the crank.
The only thing I can think of os that the spindle size is too long on the new BB but the specs (Specialzed stump FSR 2004) states it is the correct length 68 - 121.
Any thoughts please?
Thanks
md
using large front and large rear is a big no-no.
How straight is the chain when on big front and small rear and small front and big rear?
Is it hollowtech? 121 sounds long. chain should be roughly parallel to plane of frame in middle-middle cog/chainring.
And in a perfect world it will work on big-big but it's not a good idea.
Modern chainsets run at a 50mm chainline(47.5mm for earlier models, better in my opinion, but may give clearance issues with frame/rings and tyre/mech)measured from centre-line of BB shell to centre-line of middle ring.If yours is more than that, then you've got the wrong BB.
Firstly, check the middle chainring is in line with the middle sprocket.
If so, all is correct and you just need to avoid the large ring + larger sprocket combos.
If not correct, check the chainset against Sheldon Brown's database for the recommended BB axle size (I assume from your 68x121 that is an old cartridge square taper).
If still no joy, tell us more detail of chainset, rings and cassette.
PaulD