Originally Posted by
bruce19
There was a previous thread with a reference to a site that said that 25s actually rolled better (less resistance) than 23s because rolling resistance was affected more by sidewall stiffness than tire width. I was trying to get a bit more speed while improving comfort a bit. But, let me be clear, I am not having any type of problem with my current set up. Just thought there might be a benefit to 25s based on that thread.
I agree that ride comfort can be improved by going from a size 23 to a size 25. I also agree that there is no loss in performance, a 25 can be more supple and there is a performance benefit from having the tire absorb the small impacts. On smooth pavement, the 23 sized tire at very high pressure has a small performance advantage over a larger tire at reduced pressure, mostly due to better aerodynamics. However, a 23 sized tire at very high pressure forces the bike and rider to move up and over small impacts, this reduces speed on bad pavement.
I'm intensionally not trying to make an apples to apples comparison, a size 23 at 115psi will run faster than a size 25 at 95psi, if the pavement is perfectly smooth. Over damaged pavement, the size 25 at lower pressure becomes faster due to reduced suspension losses.
This report discusses the energy consumed by suspension losses:
http://janheine.wordpress.com/2010/1...-and-pressure/
I use a 700x24 on my road bike and a variety of larger tires on my Cyclocross bike. I've seen a speed increase on the larger tires on sections of pavement that are damaged or defective. I see a loss of speed with larger tires on sections of pavement that are new and in perfect condition.
If I was lucky enough to only ride on perfectly smooth pavement, I would always use a 700x23. However, my roads are often damaged: so I am faster and enjoying cycling more with the larger tires I use.