The Lowdown on Oversized Pulleys

Published October 18, 2018 05:52PM

The bicycle chain drive system has seen many technical advancements in the last decade. Today’s systems are precise, reliable, lightning quick, and provide a wide range of gear ratios—all while performing very efficiently.

A clean bicycle chain drive is about 98 percent efficient, a performance value unbeatable by gear- or belt-drive systems. In the quest for the slightest performance advantage, a few companies have brought products to market to make these high-efficiency systems even better, but improving on such a great system isn’t easy.

The modern rear derailleur uses two “jockey” wheels that are housed in a spring-tensioned cage below the cassette. The chain winds around the cassette and through the jockey wheels, maintaining chain tension in different gear combinations. When the chain moves through the jockey wheels, a small amount of energy is required to turn the actual wheels, and reducing this energy is what Oversized Pulley Wheel Systems (OPWS) aim to do.

OPWS use large-diameter sprockets to guide the chain—typically 15-17 teeth, compared to 11 teeth on a stock Shimano or SRAM rear derailleur. According to Jason Smith from CeramicSpeed (and formerly Friction Facts), an OPWS saves energy four different ways: lower friction bearings; larger pulley wheels, which require less force to turn and require less chain articulation; a slower bearing RPM; and a lighter cage tension. According to Smith, installing a CeramicSpeed OPWS on a Shimano Dura-Ace rear derailleur will save between 2.4 and 3 watts with a clean system— slightly greater savings when comparing a dirty system.

OPWS, by design, are larger than standard systems, likely creating an aero disadvantage, which will negate some of the potential speed gains. The installation of an OPWS is also a little tricky, and if your mechanic doesn’t get it just right (or if your derailleur hanger is not perfectly straight), your shifting quality may suffer.

The power savings of using an OPWS are marginal—but they do exist—and when you consider the cost, you should think about other optimizations before this upgrade. A good bike fit, an aero helmet, or a skinsuit will likely provide a greater watt savings per dollar than an OPWS for almost any rider, but if you’ve already maxed out your speed and are looking at the possibility of cutting a few seconds off your next bike split, then consider adding one of these slick systems to your ride.

Oversize Me!

CeramicSpeed OPWS

CeramicSpeed has been the go-to OPWS for the high-end triathlete. At the Kona component count in 2018, they increased their share by almost 40 percent, making them the number-one OPWS brand at the Hawaii Ironman by almost 15 fold.

SLF Motion Hyper Speed System

Considered a slightly less pricey option for a quality OPWS, SLF’s numbers increased in the Kona component count by quite a bit in 2018, but it still puts them in the underdog of pulley systems.

Digirit SRA1 Oversized Pulley Wheel System

Digirit is still not nearly as popular as the other two brands, and ordering can be a little tricky, but it’s a budget setup for a triathlete looking to dip their toes into the aftermarket jockey world.