I`d be guessing at the PSI, but its a pretty good guess. The bike I take this out with is running 700 x 23c Michlin Bi-Sports that call for between 85 and 110 PSI.

So I know from using a floor pump with a guage and a compressor with a guage that it takes 95 PSI before I start to get a tire that I can`t deform by squeezing and thats what I aim for. Checked myself a few times with the guage on the Park Tool floor pump and I`m usually within 5 PSI of 100PSI so don`t bother any more. For my weight (155lbs) its OK.

But any portable pump is an emergency tool and you need to be in reasonable shape to use any of them. The whole idea of forcing 100PSI into something requires that you exert a greater force yourself and exceptional mechanical advantage is difficult to build into a hand held unit. `Effortless` isn`t exactly how I`d describe any pump except CO2 operated units.