That app sounds like a bit of a suck and it and see gimmick for innocents. No innocents around here, though some have guileless smiles. (You can trust them. They ride a Thorn.)
In theory, I like the 15% rim drop prescription. In practice, it's purely for obsessives with time on their hands. I'd rather spend my time cycling. So what if my tyres give 1% less milage than someone who spent hours, perhaps days, measuring a 15% rim drop for all possible loading conditions? A pair of Schwalbe Liteskins 60x622 with a matching pair of Ultraleicht tubes T19A cost Euro 66 landed in rural Ireland and those tyres are still marching on strongly at 7169km, so the saving over around 10,000km is 66 cents.
Instead I propose that you test by riding, which is fun rather than work. Schwalbe, the makers of most of our tyres, give good information. I presume Pasela's makers do too, and if they don't, Dan published a reference to an Andy Blance article on tyre inflation not too long ago in another thread. So look up the makers recommendation for your tyres and and inflate to that, front and rear. Take a ride, take several rides, ride for a week or a month to see what happens when the tubes let out a little air by osmosis. If by that time you forget to follow the rest of my prescription, you've arrived, that's the right pressure for you. If you're inclined to experiment, first increase the pressure 10% and take a short ride. The purpose is merely to prove that an increase is required so infrequently as to be an ignorable condition.
Now reduce the pressure to 90% of the maker's recommendation. Why such a large initial reduction? Because those guys cover their backsides. Their marketing department doesn't want their tyres to get a reputation for giving tubes snakebites, so they bump up whatever the guys in the lab tell them is a safe pressure. Right. Now, at 90% of the recommendation, you're at the native, natural inflation of the tyres on your bike for your weight and circumstance.
Now go down another 10% of the maker's recommendation, 20% altogether. If you love this level, you can very likely safely ride here. The downside might be slightly faster tyre wear, and some tyre sidewalls may be damaged by under inflation, though generally they are damaged only by gross under inflation, not 11% real under-inflation. (This is 100 recommended minus 10% CYA margin = 90% of what the guys in white coats thought right. 10/90 is 11%.) It is unlikely that you will cause more drag by 11% under inflation, and very unlikely that you will reduce drag by overinflation; overinflation will cause faster tyre wear than under-inflation, just like on a car.
In summary: 90% of manufacturer's recommendation is very likely to give you the correct 15% drop at the rim, and to be the native, natural, necessary inflation of your tyres. A reduction to 80% of manufacturer's recommendation will give you more comfort with no or very small penalties in efficiency or longevity of tyres.
