Why do modern aero bikes look less aero?

Are today's aero bikes really faster, or is marketing just getting better? Joe Baker investigates...

- Joe Baker

Not too long ago, it was standard for every bike brand's race line-up to include an aero bike, a climbing bike, and a 'somewhere-in-between' bike. But in recent years, there's been a resurgence of the 'do it all' machine.

Trek, Specialized, Lapierre and many others have prioritised a singular race bike encompassing aero features whilst edging close to - or creeping under - the UCI's minimum weight limit of 6.8kg by merit, often, of slimmer tubing. These tube profiles appear to undermine the 'wider is more aero' rule of thumb that was often prevalent in white papers published by the same brands; there's certainly room for some cynicism here.

But despite their appearances are these modern 'aero' bikes actually faster than their deep-section counterparts? And if so what's driving this change?

Why has tubing become shallower again?

The most prominent example of shrinking - but apparently faster-tube profiles can be seen in the Specialized Tarmac SL8. The brand claimed that the bike "eclipsed the 2020 Venge as the most aerodynamic road bike we've [the brand] has ever made". When challenged at the launch event, Specialized conceded that "over 50%" of the savings compared to the old bike - with its characteristically chunky tubes - were courtesy of the new Roval Rapide CLX Carbon Cockpit.

Asked directly how slimmer tubes could be faster, Specialized's senior engineering manager Sébastien Servet told us that a lot of the change comes down to a greater understanding of aerodynamics and better testing.

"The use of shallower tube shapes in the design of aero bikes is the direct outcome changed. Firstly, the aerodynamic interaction between the bike and the pedalling rider is considered with a much greater fidelity, and secondly, a much more accurate statistical spread of yaw angles is considered in the calculation of the overall aero performance."