Originally Posted by
Retro Grouch
2. Intuitively, many folks think that skinny tires will necessarily have lower rolling resistance than fatter tires. If everything else is equal, that's not true. A skinny tire AT THE SAME AIR PRESSURE will deform more front-to-back than a wider tire. Since this deformation is what causes rolling resistance, a skinny tire will have higher rolling resistance.
Of course, it's never that simple. Skinny tires have fewer square inches of sidewall so they can safely handle more air pressure. As a general rule, bike riders use more air pressure with skinny tires which negates the rolling resistance advantage of wider tires. I think that most riders are looking at the wrong side of the equation. If everything else is equal, a wider tire will yield EQUAL rolling resistance at a LOWER air pressure. The lower air pressure will also yield a more pleasant ride.
The fatter tyre will also have more braking and turning grip, all things being equal. That's why the tyre lab referred to advised running wider rubber for crits than for TTs.
It's also important to note that
1. As roads get rougher wider lower pressure tyres reduce energy lost to vibration: this is why quite a few European racing teams use cyclocross bikes or special models of road bike that can take 28s for the rougher stages of road races. (This is close to RGs #3)
2. Most of the work a rider does at max speed on the flat is against air resistance. The faster you go, the more this applies.
In practice, if you can run them, the best tyre for an activity like commuting or touring is something like a Marathon Supreme in 35-40mm. Lots of grip, good puncture resistance, low RR at a sensible pressure.