Tour de France pros are using oversize rear derailleur pulleys. Should you?

Oct 14, 2023

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CeramicSpeed's OSPW system helps reduce drivetrain friction. Photo: Dan Cavallari | VeloNews.com

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Quick: Without going to the garage to count, how many teeth do your derailleur pulleys have?

If you guessed 11, you’re absolutely right. If you had no idea, you’re absolutely normal. It's a weird thing to know, but Jason Smith, CeramicSpeed's chief technology officer, is the kind of guy who could tell you that without hesitation.

That's because he tested nearly all derailleur pulleys (when he was the sole proprietor of Friction Facts, an independent friction testing laboratory that CeramicSpeed now owns) to see which ones save you the most watts. If you’ve been paying attention to the bikes at the 2018 Tour de France, you’ve probably noticed that CeramicSpeed's OSPW (Oversize Pulley Wheel) pulleys are on more bikes than you can count. They look kind of goofy, so they certainly stand out. But oversize pulley wheels actually offer enough of an advantage in wattage savings that it may be worth sacrificing style.

The big idea here is to reduce friction in the drivetrain. Fewer watts wasted as you pedal mean more efficiency and speed. But wait a second: Wouldn't increasing the surface area of parts in contact with each other thereby increase friction?

Technically, it would. But when you think of how a drivetrain operates — a chain winding its way over chainrings and then around a cassette, and finally, through the serpentine pulley system of a rear derailleur — the more significant cause of friction is actually the angle the chain reaches as it wraps through the rear derailleur.

So by opening up those angles and making them less sharp, the chain can articulate less than it would when it passes around smaller pulley wheels. Voila! Less friction.

Well, okay, maybe not Voila. There's actually a lot more to it than that.

"The biggest advantage is friction reduction, or increasing the efficiency of the drivetrain," says Smith. "There's a couple of ways the OSPW reduces friction. In other words, it's part of a system. The biggest factor is the larger pulley wheels. The less amount a chain has to articulate as it engages and disengages the pulley wheels, the less friction is produced. The next thing is on the larger pulley wheels, the bearings spin slower so you don't have as much drag there."

Both of those friction-saving realities are true for any oversize pulley wheel system on the market. That's just physics. But Smith says CeramicSpeed's OSPW is the fastest because there are other parts in its system that further reduce friction.

"When you get to the CeramicSpeed specific OSPW, we have our high-efficiency bearings," he adds. "The pulley wheels are a given they’ll reduce friction no matter what. And the bearings will spin slower regardless. But we design the OSPW so there's lower cage tension. So there are three settings in our system. The lower the cage tension, the less friction the derailleur system will create."

All of those factors will save you 2.4 watts when you’re pushing 250 watts, according to CeramicSpeed. Of course, those gains can go away just as quickly if your chain is filthy. All that road grit makes it more difficult for the chain to articulate, thereby adding more friction to the system. But even if your chain is dirty, the OSPW system will limit efficiency loss over a regular 11/11-tooth pulley system.

CeramicSpeed didn't invent the OSPW system. Smith says as far as he knows, the German company Berner was the first to experiment with oversize pulleys (they weren't as large as CeramicSpeed's 17/17-tooth pulley system). But after a solid initial showing shortly after development, the oversize pulleys largely disappeared. That is until Smith chose to research pulley systems at Friction Facts and came to the conclusion that oversize pulley wheels did indeed reduce friction. CeramicSpeed was paying attention to Smith's work, and the company took to task developing the OSPW.

It sounds like a no-brainer to add an oversize pulley system to your bike then, right? Not so fast. There are some drawbacks, and you’ll have to pay close attention to who makes the pulley system you’re considering. They’re not all created equal. The system isn't patented, so anyone can make them.

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"Some knockoffs will come out just with big pulley wheels with bad bearings and high cage tension," says Smith. "And the advantages aren't there because of the way it's designed. So it's not just the large pulley wheels or whatever, you need all four things [large pulley wheels, low cage tension, efficient bearings, and less lateral chain movement] working together to get the advantages."

If it sounds like we’re only focusing on CeramicSpeed, there's a good reason for that. Few other companies are offering oversized pulley wheels and its OSPW are, by and large, the pulleys of choice in the pro peloton.

Even with CeramicSpeed's system, you can run into some problems. First and foremost, the upgrade doesn't come cheap. But the $500 price aside, it's possible your shifting performance can suffer due to the lighter derailleur tension.

As you might expect, major drivetrain brands discourage consumers from retrofitting oversized pulleys to their products.

And the pulleys do hang much lower than a standard 11/11 setup. That means there's more cantilever force the derailleur has to overcome in order to shift from one cog to another. This is another trouble spot that can lead to shifting sluggishness. That's why CeramicSpeed's OSPW kit includes a carbon fiber cage to help compensate for that added force.

The price sure is tough to swallow, which begs the question: Could you get the gains somewhere else?

"Ultimately, [faster chain lube, better bearings in smaller pulleys] can all be separated out," Smith says. "You can use a faster chain lube like UFO Drip. Another way is you can retrofit larger pulleys onto a standard cage. Or you can put CeramicSpeed pulleys with high-efficiency bearings in your existing derailleur. Or — and I wouldn't recommend it —you can get into one of the rear derailleurs from major manufacturers and make a new spring tension hole to make the tension lighter. They can all be individually done for little tiny gains."

But without voiding your derailleur's warranty, or knocking your head against the wall to figure out a winning combination, you could just get an oversize pulley system. After you’ve invested in a top of the line chain lube, new bearings and/or new regular pulleys for your existing derailleur cage, you may well have spent just as much cash anyway.

CeramicSpeed remains the largest supplier of oversize pulley wheel systems, but there are many other small brands trying to make headway into the market. When choosing among them, be sure to consider more than just the size of the pulley wheel. Take into consideration the quality of bearings, the quality of the derailleur cage, the tension on the cage itself, and the ease of installation. Those are the factors that must stack up to compete with CeramicSpeed's benchmark system that you see all over the pro peloton.