Quote:
Originally Posted by andrewsuzuki
Josh Poertner's rule of thumb is +1 aero watt (@30mph) per +2mm width. Tires are kinda complicated because the top half hits the air at twice the velocity of the rider.
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Where did you see that? I've heard a different rule from Poertner, the 105% rule. That states that the rim width should be no less than 105% of the tire width for best aerodynamics. Poertner discusses the 105% rule
here.
Based on this rule, the absolute tire width is not the predominant factor, matching the tire to the rim is. For example, a 23mm tire on a 24mm rim will actually be faster than 21mm tire on a 20mm rim.