Tire Pressure Pioneer: Tom Anhalt

For an upcoming AJA episode, here’s my question:

Josh,

It seems that the Rule of 105 for optimizing the aerodynamics of the rim-tire combination isn’t guiding wheelset designs or recommendations today as much as it might have in the past.

25C models of recently introduced tires like the Conti Grand Prix 5000 TL or the new Schwalbe Pro One Tubeless produce rim-tire combinations that violate the rule of 105 on 19C and 21C rims whose outside widths are no more than 27 or 28mm respectively.

Examples, per my measurements

- Zipp 404 NSW Disc (19C, 26.5mm outside rim width), 25C Conti Grand Prix 5000 TL measures 100%, 25C Zipp Tangente RT25 measures 102% @80 psi

- Bontrager Aeolus XXX6 disc (21C, 27.9mm outside), 25C GP 5K TL measures 101%, 25C Bontrager R3 tubeless measures 101% @80psi

And more and more wheelset makers recommend 28C tires which would violate the Rule of 105 for all but 25C rims with 31 or 32mm outside widths.

Examples, per my measurements

- Zipp 303 S (23C, 27.5mm outside, hookless), 28C Zipp Tangente RT28 measures 90% @60psi

-Enve 4.5 AR Disc (25C, 31.1 outside front wheel) 28C new Schwalbe Pro One Tubeless measure 107% @60psi – a rule follower!

While physics hasn’t changed, have wider rims, new rim profiles, hookless rims, or other developments since you established the rule of 105 created a new aerodynamic relationship between the wheels and tires that suggests an update to something like the Rule of 100 or 103?

Or has the focus on the benefits of comfort, wider tires, rolling resistance, impedance, etc., made aero drag less important or increased drag from not following the Rule of 105 more than offset in the wheelset and tire’s overall contribution to speed?

Or, more cynically, has the hype and buzz around comfort, wider tires, rolling resistance, impedance, etc., pushed wheelmakers to put less emphasis on aero in the marketing of their wheels even though drag and the Rule of 105 still matter just as much?

Thanks!