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my lower jockey wheel is a plastic affair 12tooth that has no bearings just a bushing. It gives a lot of friction and a lot of side to side movement. I wish to replace it with perhaps a metal one with sealed bearings but I can only find 11tooth and 13 tooth, would either of these work and which one??

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  • The side-to-side movement is intentional. I doubt it adds much friction. I’d clean it and install it with a light grease (or maybe even chain lube). I think 13 teeth could be problematic if there is not enough distance between the pulley wheels.
    – Michael
    Apr 1, 2021 at 13:42
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    A different size may cause the chain to rub or interfere with the tab many derailleurs have in between the pulley wheels. Pulley wheel sizes also affect the way a derailleur tracks the cassette (mainly in upper pulleys) and the derailleur’s total chain wrap capacity (mainly in lower pulleys), but one tooth probably isn’t a huge difference. What is the model number of your rear derailleur? For some Shimano RDs, pulley wheels are still available from the factory, but the small parts catalog has a more recent part number than the exploded view. I ran into that issue with my RD-M772.
    – Pisco
    Apr 1, 2021 at 14:15
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    @Michael I lateral play on upper pulley wheels is definitely by design. I was under the impression that the lower pulley wheels are not supposed to have that float. Am I correct?
    – Weiwen Ng
    Apr 1, 2021 at 15:31
  • @Weiwen Ng That is correct to the extent of my knowledge. The floating upper pulley isn’t strictly required either. It helps compensate for poor indexing, but a laterally rigid pulley should give crisper shifting if you know how to adjust it right.
    – MaplePanda
    Apr 1, 2021 at 17:30

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Jockey wheels with bushings are pretty common. (NB for readers not familiar: bushings, aka plain bearings, just have the axle rotate within a plastic or bronze sleeve rather than supported by bearings. The bushing materials are self-lubricating.) Also, the plastic in question is a pretty common material for jockey wheels, and it is not intrinsically fragile in that application. That was discussed on a previous Stack Exchange post. Furthermore, the jockey wheel may appear to have relatively high friction when spun by finger, but we don't push the pedals with our fingers. The amount of friction is pretty marginal in the context of your total power output. That said, play in the lower jockey wheel is probably a sign that it's wearing out. Note that play in the upper wheel is by design.

On performance road bikes, one of the minor new trends is to replace the jockey wheels with slightly larger ones, e.g. Kogel Bearings makes 12t upper and 14t lower pulleys for current generation Shimano road groups, which come stock with 11t pulleys. However, the clearance between the upper pulley and the smallest cog is a potential issue, and some Shimano groups can only take 11t replacement upper pulleys. On the lower pulley side, there may be interference between the pulley teeth and the cage.

Thus, extrapolating to your group, if you are dead set on metal jockey wheels, it would be safest to get the 11t pulley. A larger jockey wheel may work, but it's not guaranteed. At minimum, you'd need to provide your derailleur make and model. As described in the first paragraph, I'm not convinced it's necessary for most riders to upgrade to metal pulleys and cartridge bearings. In interest of full disclosure, I did upgrade the jockey wheels on my road and gravel bike to 12/14t Kogel units, which are aluminum with ceramic bearings. That was for performance reasons, but the expected difference in drivetrain friction is small, maybe 0.5-1W at 250W input power. I have typically seen long life out of the stock plastic pulley wheels.

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  • Plastic or bronze are probably the most common bushings, but some nicer Shimano RDs used a sealed ball bearing for the tension pulley, and a sealed ceramic bushing for the guide pulley.
    – Pisco
    Apr 1, 2021 at 16:42
  • @Pisco I believe the arrangement on the current generation of Shimano road units is that Dura Ace has bearings in both, Ultegra has a bearing in one and a ceramic bushing in the other, and 105 has two bushings.
    – Weiwen Ng
    Apr 1, 2021 at 17:53
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    Looks like Ultegra has two ball bearings on R8000. Two ball bearing pulleys have been on Ultegra since 6800, XT since M773, and Saint since M820, going by the genuine parts catalog.
    – Pisco
    Apr 1, 2021 at 19:25
  • I’ve got two ball bearings in my XT M8000 RD. I believe the XTR has a hybrid ceramic bearing in the guide pulley.
    – MaplePanda
    Apr 1, 2021 at 19:33

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