>>1152469>>1152545>>1152557>>1152561>>1152651>>1152680>>1152682>>1152769The question is not wich tire is faster, the question where it is faster.
There are 2 factors that determine rolling resistance:
>deflection lossThe tire deforms under load, a bit of energy is lost to that.
>suspension lossThe tire absorbs small bumps more efficient than the rest of the bike and looses less energy
On perfectly smooth tarmac you have almost only deflection loss, so the tire deflection should be as low as possible.
Here a narrow tire pumped up to the maximum is the fastest.
On rough tarmac/gravel/cobblestone the suspension loss increases, so you need a tire that can absorb these bumps more efficiently.
Here a wider tire or airing down a narrow tire is the fastest.
In extreme cases like 100% cobble a XC might actualy be faster than a high end aero roadbike on 25mm tires.
Of course both extremes are not occuring during the whole ride, so you need to compromise accordingly, for most roadbikes this is about 25-35mm depending on where you ride and what you weight.
