Lower tire pressure thanks to wider tires or wider rim?

[cyan]

Between the rim width (taking into account both internal and external) and tire (marked) width, which has more effect on reducing required tire pressure.

For example, a 19mm/27mm-wide rim paired with a 25mm tires vs. a 17mm/22mm wide rim paired with a 28mm tires. How do we adjust/lower tire pressure between the two? Or does it all come down to the actual inflated tire width no matter the rim widths and marked tire width?

[eddief]

is there not room for air to fill the volume of the tire and the room for air associated with the volume within the rim bed itself. i think tough to measure those volumes. trust your gut and generally accepted mythology.