Originally Posted by
Sapperc
I would be careful trying to compare newer 700c wheels to old 27” wheels. They aren’t built the same externally or internally. Same goes for the associated tires. But then I’m not an advocate for under or over inflating tires. The old style 27” tires like mine are labeled “inflate to 90 PSI.” That’s how I ride them. The ride on my vintage Nishiki International is responsive, supple, and sure. No need to fix something that was never broken.
Inflating tires based on volume and load is something that basically applies to all pnuematic tires. Plus there are plenty of 700c wheels and tires built to the same quality as 27"ers.
Personally, I use the Berto tire pressure app, plug in my riding weight, bike weight and tire installed width. I treat 27" tires as 700c and run that. Technically the 8mm larger diameter of a 27" rim means more volume so they could be run slightly lower, but it's good enough.