Originally Posted by
MKahrl
Bicycle Quarterly did wind tunnel tests with rider on bike and at speeds 22 mph and below there was no measurable difference in aerodynamic drag between narrow and wide tires.
Actually it's not that simple. Those wind tunnel test measured with wind straight ahead. When it comes at an angle, the differences are greater. But more importantly wider tires impact aero wheels. That's why Zipp recomends, per the post above don't use more than 23 with their wheels