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Today I had to make a detour to the bike shop as a jockey wheel decided to fly out of a friend's derailleur. The shop were able to supply a replacement retaining bolt free of charge, however the only jockey wheels that they stocked were cartridge bearing ones at £20 a go. Needing to get home, the derailleur received an unexpected upgrade.

I did not notice any speed improvement on the way back, the jockey wheels didn't strike me as being featherlight and the shifting worked the same as before. I was beginning to wonder 'if we had been had'.

So, what is the point of expensive jockey wheels? I can see the benefit for the shop, but not for the cyclist.

ʍǝɥʇɐɯ
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    I'd never heard the term "jockey wheels" before, but eventually realized they are what I usually call "derailleur pulleys". Figured I would leave this note here for anyone else that gets the regional terminology differences confused. – rally25rs Sep 17 '11 at 02:51
  • One small and non-functional advantage is colour matching. Plastic wheels tend to be black, whereas aluminium can be anodised any colour to match the bike, and titanium has an overall lightness factor. – Criggie Jan 26 '23 at 23:48

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The advantage of sealed idler cogs is that the bearings stay cleaner and don't (in theory) need lubing. This keeps the cogs and derailer a bit cleaner, allows you to reduce maintenance slightly, and presumably provides a 0.0001% reduction in drive-train friction.

(I suspect that there was more of an advantage prior to indexed shifters, where considerable sideways force from the cog was needed to help shift the chain. In that situation wear on the bearings lead to poorer shifting. With indexed shifters (and the associated profiled sprockets and "climbing" chains) this advantage is somewhat negated.)

Daniel R Hicks
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I had repeated problems with noisy squeals on my gravel bike due to dirt getting into the bushings of the Claris rear derailleur. It was possible to clean and lube them, but it returned too often. After changing them to third-party (Tacx, but they no longer produce them) jockey wheels with sealed bearings I never had the problem again.

Now my new groupset is GRX 400 again with bushing-base jockey wheels. Let's see how long they will last before needing a service. If that turns out to be problematic, I will be looking for ball bearing replacements again.

Vladimir F Героям слава
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  • Interesting - the more-sealed the bearings are, the more drag they have. because of sealing surfaces dragging against each other. Claris was always a road groupset, whereas GRX was intended for gravel from the start. Will be interesting to see how it all holds up. – Criggie Jan 26 '23 at 23:46
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    On the other hand, sealing allows using actual bearings instead of dirty metal dragging against metal – ojs Jan 27 '23 at 12:05
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I've never seen the advantages of expensive jockey wheels, I always found that the chain wore the teeth down long before the bearings/bushes went.

cmannett85
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An independent research shop called Friction Facts ran a test in 2013 or so. Note that they’ve been bought by a firm called Ceramicspeed that sells super fancy jockey wheels, and the original paper is hosted at Ceramicspeed’s site.

They estimated that the delta between Shimano Acera pulleys, which use bushings, and the absolute best pulleys at the time was about 1.35 watts. In Friction Facts’ other work, I think I have seen them use 250W as a standard input. That is quite a high output for amateur riders. I think the drag from the pulleys should scale with the overall power input. Even so, if you lost 1.35W at a standard cruising speed, you would not be able to perceive the difference at all, barring any placebo effects.

For reference, I recently switched from standard butyl to latex tubes. At a 250W input, I think that should save me around 4-6 W for both wheels. I don’t believe that I can perceive a difference. When I flat and I change to a spare butyl tube, I definitely do not perceive a difference. Hence, while the bearing-based pulley wheels likely had lower resistance than the previous ones, you would not have been able to detect that based only on feel.

Weiwen Ng
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    The drag from jockey wheels does not scale with power output, it scales with cadence, only: The tension on the part of the chain that touches the derailleur comes 100% from the derailleur's spring and has nothing to do with the force on the working part of the chain. As such, the resistance should be a constant force that acts on the chain, and the work lost to that constant force scales linearly with the amount of chain that passes by. – cmaster - reinstate monica Jan 31 '23 at 18:07
  • @cmaster-reinstatemonica concur - the jockey wheels are on the Low Tension part of the chain path. I wonder if the resistance changes across the cassette as the angles and spring pressure changes. – Criggie Jan 31 '23 at 18:47
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    @Criggie I would think so, though I have not done measurements. Chain tension translates to force on the jockey wheels and on their bearings/bushings. And force on a bushing typically increases resistance. Thus, the more tension your derailleur puts on the chain, the higher the jockey bearing resistance. Resistance due to rust/gunk in the derailleur does not require any chain tension, though. – cmaster - reinstate monica Jan 31 '23 at 19:06
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    Both of you are right, I think Friction Facts themselves showed that the jockey wheels are under little load. – Weiwen Ng Jan 31 '23 at 22:33