It is widely accepted/proven that wider tires allow for lower rolling resistance, and (maybe less publicised) lower pressures cope better with impedance losses from rough surfaces. It is also well accepted, that wider tires take an aero hit at zero yaw, and do so even more at yaw if you go over the width of the rim.

Disc brakes are allowing tire sizes like 28mm (measuring even larger) to become a reality with minimal low yaw aero losses, offset by improved rolling resistance, and impedance losses, as the roads i frequent are not great.

Many of us are limited in tire choice due to our frames, and/or rim brakes.

It is all give an take, and your average speed, wind strength/direction, rider weight, and road surface factor in.

What combo have you opted for, and why?

To start, as a light 130lbs/60kg rider i have opted for 25mm tires, measuring 26mm at 90psi, on rims that are 25mm at the brake track, and 27mm at the widest. My reasoning is that i want to follow the 105% rule for optimal aerodynamics of my wheel, and i keep the pressures low(er) to prevent tire size from getting too large, and hurting aero. What i lose in rolling resistance with lower pressures is partly offset by my low weight, and gains in comfort, aero, and minimizing impedance.

Given the pressures i run, i estimate marginal gain scaling up to 28cc tires, wider rims (requiring disc brakes).