Giant’s new Propel Disc aero road bike was first spotted at the Tour de France, where green-jersey-winner Michael Matthews raced it on several stages. Now, a month later, Giant is revealing more about this near game-changing, disc-equipped bike and making some strong claims about its aerodynamic performance and frame stiffness. I was able to ride the bike over several days in France and test those claims.

The new Propel Disc shares no tube shapes with the previous generation Propel. Its truncated-airfoil design is similar to what is used on other aero-road bikes: a rounded leading edge with flat back. The shape - Giant calls it a truncated ellipse - was developed over three years by Nixon Huang, Giant’s senior global category manager, and Xavier Gergaud, director of Aero Concept Engineering, an independent company that helps Giant with aero designs.

Huang said the shape works better overall at wind angles from zero to 30 degrees than a traditional teardrop shape. The Propel shares other details with its competitors as well, including dropped chain stay attachment and a rear wheel cut out.

“It’s not just the frame anymore, it’s not just the fork anymore, that makes an aero-road bike an aero-road bike; it’s every single component and how they affect each other,” said Andrew Juskaitis, Giant’s senior global product marketing manager.

Consequently, part of the Propel Disc’s aerodynamic benefit comes from the frame-specific bar and stem with hidden derailleur and brake lines. Wheels are also part of the story, with a 65mm-deep rear wheel coming on all models. Up front, Giant uses a 42mm deep wheel to balance aerodynamic benefits with cross-wind stability. 

Unsurprisingly, all the newness results in a bike that Giant claims to be more aerodynamic that the previous generation. Compared to the old Propel with rim brakes, the new Propel shows about a 10 watt improvement (206.9 watts for the new Propel Disc vs 217 watts for the old Propel with rim brakes) at 40km/h. And while Giant did not provide specific data on the competitors it tested, Juskaitis said that the new Propel Disc's aerodynamic performance equals best-selling aero bikes on the market.