You seem to misunderstand this at a very basic level.

Contact patch size is not solely determined by pressure.

What other factors and how?

I do not maintain the same pressures for road riding.

Ah. I was going on your earlier post where you said they were utterly consistent in your testing.

What other factors and how?

Rim width will also influence the shape of the contact patch and the tyre profile, but I have no peer reviewed scientific data to back that up 😥

You’ve not answered the question.

I know, I was hoping you would indulge us with the correct answer.

I’ve already done so.

A 25c will have a larger cross sectional radius, and a slightly larger overall radius. It is this that I think helps with rolling over imperfect surfaces. For racing at Hillingdon, I use the same pressures (Hard!) for all tyres as the surface is perfect. For road riding, commuting etc, I use a slightly lower pressure for 25c (100/105 PSI). I’ve flatted two Open Pro rims this winter with Mavic 23c tyres, despite 120 PSI (and no pinch flat). More rubber may have helped but they were both big potholes.

The Schwalbes have a very nice tubular-like cross-sectional profile in 23c and 25c. The mavics are more “U” shaped, especially the 23c, and I think that, adjusting for other factors including rim width, this is the biggest difference. They make something of compound as well, but all nice tyres roll well.

Can’t say I’ve noticed much difference going from 23 to 25, but noticed a big difference going to 28’s.

My Michelin Pro4 in 25c are the same width as Continental Gatorskins in 28c.

I was merely pointing out that contact patch shape was another factor as it hadn’t been mentioned previously and that rim width also influenced the shape of the contact patch.
There’s some interesting research from zipp where the different attributes start to cancel each other out and if you go too big it upsets the swirl behind the tyre and how it interacts with their rim profile and creates more drag than you are gaining by lowering rolling resistance.

Reinventing the Wheel: The 25mm Revolution

http://www.competitivecyclist.com/learn/25-vs-23

http://velonews.competitor.com/2012/05/news/giro-tech-rise-of-the-25c-tire_218011

http://velonews.competitor.com/2012/07/bikes-and-tech/technical-faq/technical-faq-wide-rims-light-bulbs-and-quonset-huts_232490

Just put on some vittoria pro from chain reaction. £20 each.

Off to work in a bit so I’ll see how they feel.