Need new jockey wheel? What do I need?

[jase_31]

I have a 8 speed (Altus) and need to replace the two jockey wheels.

What do I need to get? I think it "might" be 13T and or 15T but im not sure. Can anyone advise? They seem hard to find?

 

[Slioch]

I'd go with the same size jockey's you've got on at present. These look like the ones.

 

[Gazjacko]

They should be sold in pairs as are not the same. Remember top one has play in it deliberately when fitting .

 

[screenman]

Wow! I'm all my years of cycling I have never replaced a jockey wheel, what has happened to yours?

 

[Ajax Bay]

https://www.cyclechat.net/threads/jockey-wheel-maintenance.213572/
Anyone find a decent explanation of what improvement in effectiveness using jockey wheels which are top/bottom designated (and fitted the correct way round) offer over a pair which are the same.
I've read all the stuff about the top one needing sideways float but (having searched) can find no decent explanations. Isn't the sideways float designed into the cage/bolt dimension/design?

Relatively new; (for @screenman - had done 15,000+km) should have been replaced ages ago (x2)

 

[fossyant]

Wow! I'm all my years of cycling I have never replaced a jockey wheel, what has happened to yours?

Only replaced them on an MTB, but seeing as they are running in mud and dirt, that's acceptable.

 

[Gazjacko]

The bottom one is a guide only whilst the top one has to cope with changing sprockets so needs some flexibility in its cage before the chain jumps to the new gear. Even if the look the same you might see the metal bush is slightly different to allow lateral movement.