Several years ago BQ included a seminal article on tires. I don't have that issue, but there is an article available online with some interesting data. The most recent issue (Spring 2013, available for order) goes into tremendous depth on the subject, with about 25 pages of content.
I won't rehash all the details, since BQ does a much better job than I could. But some of the highlights:
- Coefficient of rolling resistance can vary by 100% among various makes of tires. On a smooth road at moderate speeds, this might translate into a ~15% increase in power needed to ride the same speed.
- Tire pressure has virtually no difference on tire performance. Moderate pressures are in fact less efficient than lower pressures.
- Clinchers and Tubulars have virtually identical performance characteristics, except that a tubular can be run at lower pressures which improves performance on rough roads
- Wider tires of the same make offer the same performance as skinny tires on smooth roads. On rough roads wider tires provide far superior performance.
- The 'fastest' clincher BQ tested is the Vittoria Open Corsa Evo CX. The various Grand Bois tires are ~0.5mph slower at 150W. A typical mass market tire (Michelin Pro2 Race) is another 0.5mph slower. Lots more detail (not from BQ) here.
- Flat resistant tires exact a significant tax in rolling resistance that is hard to justify for long distance rides on paved roads.
- Tire tread can, contrary to some assertions, provide assistance with wet traction and even puncture resistance. That does not, of course, mean that the tread most tires have helps with either.
The journal of course goes into far more depth on the testing methodology and results. I'd recommend it to any distance cyclist. Of personal relevance, I'm using Schwalbe Ultremo ZX 700x28 tires on my Habanero rebuild (primarily out of vanity, they look really sweet!). For a fatso like me, this probably puts my ideal tire pressures at about 80psi front, 95psi rear. BQ of course includes a handy graph for calculating your own tire pressure.