Originally Posted by
mstateglfr
Yan - how many watts slower is a 40mm smooth tire vs a 32mm smooth tire due to wind resistance?
I genuinely don't have a number or formula. I have read articles that said in wind testing, it is less than the difference between rolling resistance for a good tire and a cheap tire.
But again, I don't have a formula or actual number.
You have argued the point, many times, that wind resistance is gonna get ya at 40mm so it's best to drop to 32m.
What controlled testing is that based on? I honestly don't know what the difference is and am curious.
I have bikes with 26mm, 27mm, 32mm, 38mm, and 43mm tires right now and some are the same brand and model. Curious to know.
It's going to make almost no difference at touring speeds. Every 10mm wider tire gives you an extra ~70cm2 frontal area, turned into a square would be 8.4x8.4cm, equivalent to about 1/4 the wind resistance of hanging one front pannier. Wind resistance isn't a major factor in tire width selection for touring because we're barely breaching 20km/h.
Not sure about watts, maybe you could find something via Google where someone's done some wind tunnel testing. Most of the product manufacturers wind tunnel test at 50km/h to amplify their marketing spin. Not sure if anyone has ever tested at 20km/h. It'll probably be some absolutely tiny number, like less than one watt.