SRAM sues Princeton Carbon Works for patent infringement of wavy rim on aero wheels

SRAM is suing Princeton Carbon Works for infringing a patent relating to an undulating rim design that is said to reduce aerodynamic drag and side force, which is a factor when riding in crosswinds.

SRAM says that the wavy rim shape on Princeton's 6560 carbon road wheel infringes its patent for the rim design that features on its Zipp 454 Carbon NSW wheels.

“SRAM's wheels rely on two patents from inventor Dimitris Katsanis. The first patent was issued in 2017 and a related patent was issued in 2020. Katsanis assigned both to Metron IP Limited, a Nottingham, UK, company, who in turn assigned them to SRAM. It's not clear when the patent was assigned to SRAM,” Bicycle Retailer reports.

Katsanis is best known in the cycling world for designing track bikes used by Team GB. 

SRAM’s patented rim shape is in part inspired by a humpback whale, with the "Hydrodynamic Design of the Humpback Whale Flipper," published in the Journal of Morphology in 1995, cited in the patent. The SawTooth design came from the irregular shape of the leading edge of humpback whale pectoral fins.

Princeton Carbon Works is a relatively young US performance wheel brand that arrived on the scene in 2018, conceived by a group of engineering graduates from Princeton University.

Princeton’s Wake pattern is said to have taken four years of development, and what you are left with is a rim that contains 24 sinusoidal oscillations, giving a depth that varies from 60mm to 65mm.

"Advanced aerospace engineering facilitates better speed through the breakthrough of dynamic cross-section variability – WAKE – which yields lower drag and reduced effects of vortex shedding," says Princeton.

Stu Kerton recently reviewed Princeton’s Wake 6570 Disc Tune wheelset and his full review can be found here.

The depth of the Princeton rim and the Zipp rim each vary, but the Princeton undulations appear symmetrical while the shape of Zipp’s is more like a sawtooth.

SRAM complains that Princeton was aware of the SRAM patent and continued to market its wheels. SRAM is asking for tripled damages for willful infringement and for Princeton to be ordered to deliver up for destruction any remaining inventory, according to Bicycle Retailer.