I just changed my cassette from a 32 to a 34. All is good but on the big sprocket in the front it will not change properly on the big sprocket on the rear. On the small sprocket on the front it will shift good onto the big big sprocket on the rear. What am I missing? Adjustment or a longer chain?

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    Can you please add the rear derailleur model and cage size, and your front chainring sizes to your question. – Argenti Apparatus Oct 1 '18 at 1:06

If you can change to biggest sprocket on the small chainring, sounds like the chain is too short. If it's new you can add a link in (if you have the left over links), otherwise you'll need to replace and resize the chain.

You should probably also check that your rear derailleur can take a 34 tooth max cassette sprocket, and you have not exceeded the derailleur total capacity (difference in chainring tooth counts plus difference between largest and smallest sprocket tooth counts).

  • Agree with this. It's usually a good idea to replace your chain when you replace your cassette anyhow. You may be able to improve shifting by tightening the "b" screw on the back of the rear derailleur, which will change the angle it hangs at. Finally, there is a gizmo that lowers the whole derailleur, which might help if nothing else does. – Adam Rice Oct 1 '18 at 1:55
  • I did adjust the derailleur ( a bit lower ) have not adjusted the angle of the derailleur. How do I do that? – Creighton Oct 1 '18 at 2:57
  • @Creighton Tightening the B screw moves the top idler away from the cassette (i.e.,'lowering it'), but also changes the derailleur angle as a side effect due to the derailleur rotating around the B pivot. There are no separate height and angle adjustments. – Argenti Apparatus Oct 1 '18 at 3:05
  • If the derailleur couldn't cope with the cassette, wouldn't it be unable to shift into the big cog from the small chainring, rather than just the big one? – David Richerby Oct 2 '18 at 13:00
  • @DavidRicherby Yep, that's why I think it's chain length, but recommended checking derailleur specs. Messing with B-screw 'aint gonna fix this. – Argenti Apparatus Oct 2 '18 at 13:05

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