Originally Posted by D1andonlyDman

Well, here's the counter-argument: As I am no longer a Clydesdale, having gotten just below 195#, I decided to mount 23s on my fastest bike last night. And today, first time on the skinnies, I shattered the lap times I'd been running on the local circuit around my house that I normally ride, knocked my times down 4-5%: I went from lap times in the 7:15 to 7:20 range running 25mm tires inflated at 8 bar, to consistent times in the 6:50s on the 23s inflated to 9 bar. I could not believe how much faster I was on the skinny tires. Yes, they give a firmer ride. And I just about never flatted on the 25mm tires - who knows how the 23s will do on that score. But 4% faster is nothing to sneeze at. I can't imagine how anyone could race on 25s after that experience.

Originally Posted by D1andonlyDman

Well, here's the counter-argument: As I am no longer a Clydesdale, having gotten just below 195#, I decided to mount 23s on my fastest bike last night. And today, first time on the skinnies, I shattered the lap times I'd been running on the local circuit around my house that I normally ride, knocked my times down 4-5%: I went from lap times in the 7:15 to 7:20 range running 25mm tires inflated at 8 bar, to consistent times in the 6:50s on the 23s inflated to 9 bar. I could not believe how much faster I was on the skinny tires. Yes, they give a firmer ride. And I just about never flatted on the 25mm tires - who knows how the 23s will do on that score. But 4% faster is nothing to sneeze at. I can't imagine how anyone could race on 25s after that experience.

Originally Posted by alcjphil

The question that I would ask is if the new tires were otherwise identical to the old ones. Basing a comparison on tire width alone isn't valid unless the new tires are the same make and model as the old ones. When I switched from a puncture resistant 25 mm tire to a more supple racing oriented tire I noticed a difference in both comfort and rolling resistance

Originally Posted by D1andonlyDman

Very similar, but not identical. The 23s were Vittoria Rubinos IIIs, the 25s were Forte Pro+, which are basically copies of the Rubino IIIs, with the same specs and same type of construction. Previously, I've used both in 25 size and couldn't tell the difference between them in ride characteristics, and in my times.

Originally Posted by dbg

If the course is very smooth, I would expect skinny, high psi to be faster. But I have been in pace lines on very rough courses where we suddenly cross a county line and the road goes total glass smooth. The speed of the pace line instantly goes up by 3 or 4 mph. I try to imagine a similar effect by switching to super light, soft/supple, wider tires --to smooth out the harsh ride.

And even if I'm not in a pace line or racing (I never do), banging over harsh expansion joints all day long on 23s at 120psi is not something I ever want to do again, ever.