Problem with jumping gears

rugby bloke

Veteran
Location
Northamptonshire
I ride a 2018 Giant Defy 3, bought new on August and fitted with a Tiagra groupset as standard. Up to yesterday it has run trouble free. On my commute last night the chain started jumping between cogs on the rear cassette, usually down the cassette.
The problem seemed to be worse when I put more power through the pedals so I cruised home on half power.
I'm guessing that something needs adjusting, it would be great to have some advise as to what that something is !
 

Vantage

Carbon fibre... LMAO!!!
Is your indexing out?
 
It sounds like indexing. You should have an in-line barrell adjuster near your bars. It's accessible as you ride, so you can adjust it to see if you can tune it out. Turn it, if it gets worse turn it the other way. Also, check your derailleur to see nothing is caught in it and it hasn't been knocked and bent.
 
OP
rugby bloke

rugby bloke

Veteran
Location
Northamptonshire
Thanks for the feedback - I'll check out the indexing, most likely with the help of YouTube. The road out of Wellingborough station has been dug up and is in shocking state so I guess something could have been thrown out at this point.
 
Location
Loch side.
The road out of Wellingborough station has been dug up and is in shocking state so I guess something could have been thrown out at this point.
No. That's not the cause.
 

si_c

Veteran
Location
Wirral
As mentioned above, the derailleur is no longer setup correctly to mate the chain position with the sprockets at the back. This can be caused by a number of things, most likely re-indexing will fix the problem but before you do check the following:

1. Is the derailleur hanger straight.
2. Is the rear wheel correctly seated in the drop-outs - you'll be surprised on rough roads that it can move out of position.
3. The derailleur cage is straight and not bent in any way.

If those things are ok, it's time to twiddle the barrel adjuster - if the chain is jumping down the sprockets (i.e. away from the wheel and into a higher gear) turn 1/4 anti-clockwise and see if that fixes the problem, if not try another 1/4 later. If it goes the other direction up the cassette (closer to the wheel) then do the same but turn clockwise.

Also make sure that the chain is actually shifting over sprockets and not slipping - this is a completely different sensation when riding, but it's easy to confuse the two if you're not familiar with them both.
 
Last edited:
OP
rugby bloke

rugby bloke

Veteran
Location
Northamptonshire
As mentioned above, the derailleur is no longer setup correctly to mate the chain position with the sprockets at the back. This can be caused by a number of things, most likely re-indexing will fix the problem but before you do check the following:

1. Is the derailleur hanger straight.
2. Is the rear wheel correctly seated in the drop-outs - you'll be surprised on rough roads that it can move out of position.
3. The derailleur cage is straight and not bent in any way.

If those things are ok, it's time to twiddle the barrel adjuster - if the chain is jumping down the sprockets (i.e. away from the wheel and into a higher gear) turn 1/4 anti-clockwise and see if that fixes the problem, if not try another 1/4 later. If it goes the other direction up the cassette (closer to the wheel) then do the same but turn clockwise.

Also make sure that the chain is actually shifting over sprockets and not slipping - this is a completely different sensation when riding, but it's easy to confuse the two if you're not familiar with them both.
Thanks for this, very comprehensive, I will check all of these tomorrow night. I've got a Sportive on Sunday so hopefully I can make it better rather than worse ...
 

si_c

Veteran
Location
Wirral
Thanks for this, very comprehensive, I will check all of these tomorrow night. I've got a Sportive on Sunday so hopefully I can make it better rather than worse ...
If you only turn the dial one way then you just have to remember how many turns you made and you can always get it back where you were.
 
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