Directional Tension Pulley???

andulong · Nov 8, 2009

Ok, this is just a question asked out of curiosity. I am not having any problems with the bike. Today when cleaning up the rear derailleur (Ultegra) I noticed that the tension pulley has directional arrows on it. I can not see any difference in the teeth design or the way it spins. Looks the same from both directions, why directional? The guide pulley is not, at least it is not marked. I searched online but could not satisfy my curiosity.

Thanks.

Kerry Irons · Nov 8, 2009

Rotating right

andulong said:
Ok, this is just a question asked out of curiosity. I am not having any problems with the bike. Today when cleaning up the rear derailleur (Ultegra) I noticed that the tension pulley has directional arrows on it. I can not see any difference in the teeth design or the way it spins. Looks the same from both directions, why directional? The guide pulley is not, at least it is not marked. I searched online but could not satisfy my curiosity.

Without having a pulley in my hands to examine, I'll take your word that they are completely symmetric. If that is the case, then the directional arrow is just like the directional arrow on many tires; they put it there to keep people from bugging them if the item has to be mounted in one direction or the other. Campy pulleys are the same way, but it's not obvious that they really need to rotate one way or the other. Next time I have the derailleur apart, I'm going to check this out

Chainstay · Nov 8, 2009

Maybe it's for those who are mechanically challenged to show them how to route the chain through the derailleur pullies

Nielly · Nov 8, 2009

On the Campy the directional arrow does indicate the pulley rotation. The pulleys are symetrical when looked at from the side but if you look at them end-on you can see that the teeth are profiled - narrower in the front.

kbiker3111 · Nov 8, 2009

This has always bugged me too. I haven't been able to find a lack of symmetry, so I run them whichever way the go in.

andulong · Nov 8, 2009

Ha, Ha

Chainstay said:
Maybe it's for those who are mechanically challenged to show them how to route the chain through the derailleur pullies

In that case, it would be fun to put it on backward and see what they could do with it!

wim · Nov 8, 2009

It is directional, for a while.

andulong said:
I can not see any difference in the teeth design or the way it spins.

If you look closely at a new or almost new Ultegra derailleur tension pulley, you'll see that there are chamfers leading up to the front edge of each tooth. As the pulley wears, these chamfers pretty much disappear into the general wear pattern and the pulley becomes (and looks) more or less symmetrical.

Directional Tension Pulley???

andulong

Kerry Irons

Chainstay

Nielly

kbiker3111

andulong

wim

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