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SubscribeKCNC Ceramic Derailleur Pulleys
Tue, 01/12/2010 - 10:03pm by Andy
I received some KCNC ceramic pulleys from Fairwheel Bikes, a Tucson bike shop known for its eclectic inventory of specialty parts. Aside from being anodized in pretty colors, these pulleys promise better shifting thanks to a bit of lateral float, as well as less drag from its ceramic bearings.
In terms of float, these pulleys fall between Shimano (lots) and Sram (none). My Sram drivetrain did seem a tiny bit quieter with KCNC pulleys installed, but the difference was so tiny that it could have been my imagination.
The real interesting claimed benefit of these pulleys is reduced drag. Fairwheel's site claims that derailleur pulleys are the best place for a bearing upgrade, since they're the fastest spinning bearings on the bike. If you pedal at 100 rpm, your pulleys are spinning at 481 rpm's in the big ring, and 355 rpm's in the little ring (53/39). The faster the bearings spin, the more watts they suck up, so the logic goes. I have my doubts about this, since derailleur pulleys see far less radial load than wheel and BB bearings, and load also increases bearing drag. But since I have no way of testing this, let's just press on and see if these pulleys do decrease drag compared to stock pulleys.
There's two ways to reduce pulley drag: upgrade the bearings, and use a larger, slower spinning lower pulley (you can't put a bigger one in the upper position). A quick spin test immediately raised doubts as to the quality of KCNC's bearings – Sram's pulleys, also with ceramic bearings, had much less drag. Perhaps this is a good time to harken back to what Josh Poertner of Zipp said about ceramic bearings (cheap ceramic bearings are made to withstand heat, and don't necessarily spin faster), as well as the fact that Rich Sawiris of Wheelbuilder.com only recommends Ceramic Speed bearings (Ceramic Speed pulleys go for $140 on Fairwheel's site, KCNC, $35). KCNC's bearings may be ceramic, but they sure don't seem fast.
Next I tested the pulleys on the rollers, with a Quarq Cinqo crank and a PowerTap wheel. Since the Quarq is upstream of the pulleys and the PowerTap downstream, drivetrain drag should show up in the difference between the two power readings. I rode with a constant cadence using a metronome, and I did runs in both the big and little rings. Runs were done on Sram, Shimano, KCNC 11-11, and KCNC 11-12 pullleys.
Sadly, the differences involved were all well within the claimed margins of error of the Powertap and the Quarq. The only conclusion I might draw are that the Sram pulleys seemed 4 or 5 watts more efficient. But to reiterate, this was all within the margins of error for the two power meters.
Lastly, I tested one more theory from Fairwheel's Emiliano Jordan. He thinks that for the same gear inches, you're better off riding in the little ring than the big ring. The thinking is that when you're in the big ring, the rear derailleur is more stretched out, and that extra spring tension puts a radial load on the pulleys which increases drag. I ran the same pulleys in the big ring and small ring, pedaling at 100 rpm in the small ring and 74 rpm in the big ring so that the pulleys spun at the same speed, and got almost identical numbers.
So what's the moral of our story? First of all, things that make sense logically may not pay off in terms of real world benefits. Secondly, all ceramic bearings aren't created equal, but lesser bearings in your derailleur pulleys will probably only cost you a watt or two. Based on my somewhat inconclusive tests, I'd have to say that derailleur pulleys aren't the best bang for the buck for a bearing upgrade. But there's a silver lining. One of my Sram pulleys split, causing my chain to occasionally pop off and lodge between the pulley and the cage. I happily swapped out the composite pulleys for the KCNC aluminum pulleys.
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Add a commentI like the jig idea, but you still need something to measure the drag the pulley is causing. So something to spin the jig at a measured rate and pressure (torque) and then calculate the difference? Something like that.
From the previous post you can get the jig but then you still need the saw. You can't go "I solved it, I solved it!" and then when people ask you for the solution and you only have a jig and no saw, they would go "You have not saw!" and then you'll be the laughing stock of the scientific testing of pulleys world. I suggest you ask Lorenzo Rivnut for a saw.
I propose you create a jig to test the pulleys. You could use the remains of an old derailleur. Mount the pulley in the cage, use a torque wrench to get the preload the same during your test. The take a chain and loop it over the pulley. Add a 10lb weight to one side of the chain and a 5lb weight to the other. Raise the 10lb weight 3ft off the ground and do several timed drops to see how long it takes to reach the ground. Average out the number and see what you get. Then repeat with the other pulley/s.
Gripes! Twice! The Sky is falling on the Shack! The season is already long...
You can't imagine? Good thing the writer quantified it then. Thanks for your unverified musings though.
I cannot imagine that any of this makes a damn bit of difference in the real world other than as a negative i.e. worn/dirty or otherwise compromised bearings might create a little extra drag. but really the only thing that matters on a bike is aerodynamics (somewhat) and the quality of the rider.
As far as I could tell they're interchangeable.
Hey Andy,
Very cool, thanks for writing up your test results.
Do you think Sram red ceramic pulleys would work well with DA7900 derailleur?
Mark Twain drank Old Crow
it's like comparing Basil Hayden and Pappy Van Winkle Bourbon. Both are excellent. By comparison, comparing Old Crow and Pappy Van Winkle, and you will know the difference immediately.
Well maybe testing some really ratty pulley's would prove disprove your hypothesis? If some pulley's off a $100 bike (new) show the same result then, yes you are right. Comparing top of the line vs supposed top of the line might not show much difference. I'm not saying it will prove the ceramic's are better just that any pulley will be the same.
Now to find some ratty pulley's?
Been working the last couple of days, catching up on some questions.
Spin test wasn't claimed to be accurate, but I think it lent some insight into the quality of the bearings.
Slope measurement for each power meter was not necessary. I was looking at the change in the relative measurements, so as long as they were consistent that was good enough. If I wanted to know the % power lost in the drivetrain, then I'd need to measure the slopes and y-intercepts and have a good grasp of the absolute numbers.
Gearing was the same for all the runs, very obvious factor to control for.
I don't NEED better test equipment. My aim was to test a marketing claim (these pulleys save power) because false advertising bugs me, and I think I did enough to say that claim is dubious at best.
As for 'the final straw', you need to work on your reading comprehension. The point is that these things DON'T help you, and that just because some bearings are ceramic, doesn't mean they're better. The $140 pulleys might really be better, but I doubt they'll help you much either.
What matters is parasitic loss under load, not freely spinning.
As mentioned, the results are within the margin of error. Additionally, you would need to do a measurement of the slope of each powermeter (with a known weight) in order to ensure the meters are correctly reading the proper numbers. Additionally, different f/r gear combinations have differing amounts of drivetrain loss, so you would need to factor that in as well. (Human Power 52 summer 2001, Chester Kyle and Frank Berto, Human Power 50, Spicer (with subsequent analysis in 51 by Walton & Walton)
http://www.chroniclebooks.com/index/main,book-info/store,books/products_...
Eben gets about a million per, he's that good at blowing Lance.
Ouch! How many extra web hits is a blowjob worth these days?
I'm so excited about this development. For years I've been feeling like my derailleur pulleys have been holding me back, keeping me from making the big jump to Cat 3. This is almost as revolutionary as the internal headset.
tiso
I think "the moral of the story" is you need better test equipment. At least to get the numbers you need or more accurate ones.
I heard the Aluminum pulleys were noisier than those plastic-ish ones? What's the word on that?
I bought some a while back (different brand) and thought they were less draggy (no solid data, of course) and the red bearing cover looked cool (hey at least I admit it)
"This is called "cabin fever." One day you're compulsively spinning derailleur pulleys, and the next you're talking to a volleyball and roasting and eating your housepets."
Eben had some downtime from blowing Lance?
Snap!
Oh no he didn't!
Thanks Andy. Now I have confidence that I am doing the right thing by buying beer instead of cermaic pulleys.
Here's my logic. The pulleys are on the lower run of the chain, so it should be independent of power. I kept chain speed constant, used the same gear combo, so the power output was pretty consistent anyway. But the key number is the difference between the two power meters on the same run, so some inconsistency between runs shouldn't matter too much.
I didn't use a torque wrench to make sure each pulley was installed with the same bearing preload, though.
Your last detail - the SRAM pulley coming apart -- made me wonder: ss there any difference (quality, durability) between composite/plastic pulleys like the default Shimano D/A, and replacement aluminum ones, all bearings being equal?
not to nitpick, as I know you don't claim this is scientific, but the "spin" test you employed is hardly reliable. who is to say that (a) you spun each with equal force, and perhaps more importantly, (b) you held each pulley with equal force?
Perhaps a coast-down test from a given speed (on rollers or a trainer) with the only difference between each run being the pulleys might be more appropriate?
You may not pick up any watts with new pulleys, but they can significantly increase performance. I just switched out the pulleys on my winter bike with Shimano 105 shifting. I put in something similar to what you are reviewing here except they have steel bearings in a sealed cartridge. It only cost me $35, and it works as well as the Campy Chorus on my race bike.
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