Indexing: stand vs on the road (gears jumps when I pedal)

[Ugo51]

Hi guys,

I'm having some issues indexing gears on one of my bikes (Shimano Claris 2x8 ).
I just istalled a new chain (Shimano) and all is fine on the stand but when I actually try to ride, the chain tries to jump to the inner cog, as if there was excessive tension. What could it be?? The chain is admittedly very close to the inner cog, almost as if it's too thick...
On the way to work (with another bike) I thought it could be the wheel not mounted correctly, but the bike has vertical dropouts...
It's a bit frustrating as the problem only presents itself when I apply a good amount of torque on the pedals. On the stand, or if I pedal lightly on a flat road, all is fine. As soon as I start pushing...clack, clack, clack...

 

[dookie]

Sounds like new chain/old gears. How to the cog/ring teeth look?

 

[Ugo51]

Ah! I didn't know that matching a new chain with old cogns would give that problem!
The cogs are not terribly old (only 7500km) and look fine to me, but I will take a picture tonight and upload it here. Maybe they are more worn out than they look to me

 

[SF Klein]

Might also want to check out this article…
https://www.sheldonbrown.com/autoshift.html

 

[Ugo51]

Thanks.
My problem is slightly different though. It tends to shift to the next larger cog.

I will double check the cable guide, but I think it's fine. I just replaced the cables and cable housings a couple of weeks ago

 

[ishaw]

I have had this happen, perfect in the stand, slightly off in use. MTB shifters make this easy to dial out while riding, using the cable adjusters on the shifter. Not sure of it's as easy on road shifters.

 

[Ugo51]

Not as easy. I could use the dial on the downtube.
But that's not the point, as it doesn't depend on the tension. It just does it no matter what...
I could try swapping the chain with another one, but maybe it's wiser to wait for the new cassette first.

 

[hamster]

I've had exactly that, unpredictable shifting and jumping between gears with a worn cassette.

 

[novocaine]

answer is already covered above, your cassette is fubar.
really I just wanted to make a point.
It does seem to be more of an issue these days, I used to swap chains 3 or 4 times before replacing a cassette, now it seems like I have to replace it every other change (or every chain in some cases as I do like to forget about it till it's to late). I do wonder if modern chains are built to tighter tolerance so it results in less wear resulting in greater issues.

there is a cassette wear gauge available, but I'm not sure I trust it as it's a bit ambiguous in it's results.

(note, cheaper versions are available)
https://www.ebay.co.uk/itm/12391112...juDjoKjGghAGL0_M8Ja9PMVx2Uy6vpwxoCq_IQAvD_BwE

 

[Ugo51]

I do wonder if modern chains are built to tighter tolerance so it results in less wear resulting in greater issues.

...or the new cassettes that wear out quicker?

I've ordered a new cassette, which should arrive in days. Unfortunately I am working late hours these two weeks and I can't pick it up from the shop