[Lio]

Fast Fitness produced a little spreadsheet to calculate optimal pressure based on tyre width, bike+rider weight and a very granular assessment of surface.[1]

Something else to take into account is the aerodynamic trade off as tyre width grows. I think I read somewhere that 25mm is roughly the sweet spot. What you gain in lower rolling resistance by going up to 28mm you loose in drag. That's a bit anecdotal (sorry) but I have heard it mentioned in a couple of places. The best source I could come up with was from Zipp's web site.[2]

Of course that might well be worth it to be more comfortable if it means you can keep your body in a more aero position as that will dwarf any loss from the tyres (again a guess).

Hopefully there's some numbers somewhere to back that up. Maybe Bicycle Quarterly or Tour Magazine might be a good bet for anyone interested.

Also https://www.bicyclerollingresistance.com/ is always very interesting ...assuming you obsess over bike tyres as I'm sure everyone does. :P

[1] https://www.youtube.com/watch?v=Clk_LLBYFzA [2] https://zipp.com/support/faq/faq.php