Originally Posted by Sy Reene

Never liked the SRAM calculator, because it is inferring how wide your tires will be for a given rim width, even though it's quite known that different manufacturers nominally label their tire sizes differently versus how they actually inflate. It also only has 2 road surfaces to choose from -- Dry or Wet. Nothing to do with actual texture -- eg. rocky, smooth, dirt, etc. And then of course, since they're heavily invested in selling the hookless variety of wheel through Zipp, I expect their bias on PSI recommendations is always going to be on the low side in order to satisfy the marketing side of their business.

For any calculator, what none of them seem to ask for is the inflated height as well. Even sites like BicycleRollingResistance, will show the inflated height as well as width. I presume a taller inflated height means more air volume than a lesser height (for an equivalent inflated width, and there are sometimes fairly significant differences between tire brands on inflated height.