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Wheels of fortune: oversize pulley wheel systems

27 Apr 2021

Main image above: Ceramicspeed OSPW, buy now from £289.99 at Wiggle 

It’s a small component, but the effect an oversize pulley wheel system can have on drivetrain performance is surprisingly big

Words: Sam Challis Photography: Rob Milton

The oversize pulley wheel (OSPW) system was pioneered by engineer Wolfgang Berner, and it set internet forums ablaze when it was first spotted on the Sram Red rear derailleurs of Fabian Cancellara, the Schleck brothers and Lance Armstrong during the 2010 season.

‘What is this rear derailleur thingy?’ was the topic headline of countless threads, accompanied by a grainy screenshot of Spartacus at his imperious best in one of the two time-trials at that year’s Tour de France (he won both).

Andy Schleck won the 2010 Tour (admittedly only after the original victor, Alberto Contador, was disqualified after testing positive for clenbuterol that he claimed came from contaminated steak), which added fuel to the discussion surrounding the benefits of the design.

Berner is no longer a name in the OSPW space but the concept has since moved from esoteric to mainstream and the claimed benefits to drivetrain efficiency are well known.

Anything up to 4 watts can be saved by upgrading stock cages to an oversize system. It is said that a new Shimano Ultegra groupset costs 20 watts of a 250 watt effort at 90rpm, making a standard drivetrain setup 92% efficient. Oversize systems claim to move that figure up to 94-95%.

As an aside, a good lube choice and fastidious cleaning regimen on top of a cage upgrade can bump that figure even higher, although 100% efficiency is impossible to achieve.

Muc-Off LOPS, £tbc,

It’s a gain that may appear to be inconsequential to some, but for the many who subscribe to the marginal gains school of thought the upgrade is well worth making. So how are these gains made?

Stock pulley wheels – the kind found as standard on many rear derailleurs from Sram, Shimano or Campagnolo – tend to have 11 or 12 teeth each, whereas oversize systems use pulley wheels with up to 19 teeth.

‘Larger pulley wheels decrease the amount of articulation required from the chain links,’ says Ard Kessels, founder of Kogel Bearings.

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‘As friction is created through chain plates sliding back and forth when articulating, there is less friction created when the chain moves less. Additionally a larger pulley wheel rotates slower than a smaller wheel, reducing bearing speed and therefore bearing friction.’

‘A well-designed oversize pulley arrangement will also allow for customisation of the cage’s backward spring tension,’ says CeramicSpeed’s Paul Sollenberger.

Kogel Kolossos, buy now from £290.80 from Ebay

‘Friction is further reduced by the use of a lower spring tension, which allows the chain to articulate more easily through the derailleur cage.

'Plus the larger pulleys will actually wear at a slower rate than smaller pulleys because each tooth contacts the chain fewer times during each chain revolution and the wheels are made from machined aluminium rather than plastic.’

Ironing out the imperfections

This promised longevity, as well as performance-enhancing capabilities, helps to offset the OSPW’s invariably high cost, but over the years the design has been met with some reservations about its effects on shift quality.

There have been reports that because the larger wheels need longer cages, old systems’ lower lateral stiffness made gear changes sloppier.

Interestingly the current crop of designs all go about solving this issue in a different way. Kogel’s Kolossos goes for I-beam-inspired machined aluminium to house its wheels, while Muc-Off plumps for 3D-printed titanium in its LOPS system.

Token Shuriken, £289.99,

Both brands claim their designs are significantly stiffer than stock cages. CeramicSpeed’s OSPW goes for injection moulded carbon fibre and Token’s Shuriken uses machine-cut, woven carbon composite.

‘We also have purpose-specific tooth profiles to promote crisp and silent chain engagement,’ says Jerry Lin, Token’s head of R&D.

The exotic cage materials and designs help keep weight to barely greater than stock models. Current generation stock cages that cater for increasingly larger sprockets mean that OSPW systems aren’t physically larger (and therefore more vulnerable to impact) anymore either.

‘We just take better advantage of the space within,’ says Sollenberger.

The question remains, however, if these systems have been around since Cancellara and the rest sported them back in 2010, why don’t we see them throughout the pro peloton these days?

Recently Muc-Off’s LOPS system was used by Mikel Landa on Stage 20 of the 2020 Tour, and CeramicSpeed has spent some time aboard the bikes of AG2R-La Mondiale, but that’s about the extent of it.

‘The primary resistance we meet for broader adoption is existing sponsorship agreements with other component brands,’ says Sollenberger.

There’s little doubt that it would happen otherwise, such are the component’s advantages. Happily, though, most of us have no such concerns.

So if your wallet can take the hit, upgrading your rear derailleur cage may just be worth it, for the style points if nothing else.