Just for comedic relief, I built up my Medici, this time with new (to me) stem and bars and a 12-25T cassette that I thought was a 12-27? I don't know...
Anyways, 25mm tires on the gauntlet of the side street my apartment building is on. It's as if it says, rather immediately, "ARE YOU AWAKE?"
Bad news: impacts are FELT, NOW. High level of kick, so that's not fun. Good news: The tires, wheels, and frame "stop" the vibration festival quite quickly. No "quivering." And then once on good roads, it's time to fly.
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So, in my (presently futile) search for a unicorn Big Tire But Not Disc Brakes Touring-ish bike, I keep coming across the same few JH articles on tire size and all of this, so I decide to have some calculator fun and look at both nominal and actual tire diameters to see how various larger (Soma Supple Vitesse EX) tires compare to my "33mm" Soma Supple Vitesse EX's with respect to tire volume.
So let's take, per JH calcs, but for me, a 33mm tire (nominal), the Soma SV EX. It's air volume will be "100%" and any size smaller or larger will work from that bogie.
28mm - 615mm^2 - 72% (just for kicks)
33mm - 855mm^2 - 100%
38mm - 1,134mm^2 - 133%
42mm - 1,385mm^2 - 162%
48mm - 1,809mm^2 - 212%
You can see that a 38mm tire struggles to attain (what I term) "escape velocity" with regard to appreciable increase in volume. 33% volume improvement is good/fine, but in my direct experience, didn't have me feeling it was that beneficial. 42mm tires have 62% more volume, so now we're cooking a bit. And of course, bumping to 48mm tires has us over double the air volume, and that is definitely felt, and for the (much) better.
So let's get Real World (TM) here. 30mm is my actual tire size for the 33s, and 45-46mm was my actual tire size for the 48s (sorta averaging 13mm internal and 16mm internal rims' results). I guestimate that 42s would measure 40mm, so now let's use 30mm tires as "100%":
30mm - 706mm^2 - 100%
40mm - 1,256mm^2 - 178%
46mm - 1,661mm^2 - 235%
Impressive "work" by the 42s IMO. Nearing or nearly double the volume! But then you have the
sweet sweet siren song of well over 2x the volume with the 48s at a whopping 235%. This is why I am on a mission with those 48s, aside from the fact that I got them essentially new and for so cheap.
Next, I move to estimated tire pressures of a 42mm tire were I to run it. (F/R in PSI)
33mm (30mm) - 70/75
42mm (40mm) - ?/?
48mm (46mm) - 38/40 (or 40/40)
I calculated things using actual tire diameter proportion/relation to each other, but not volume, and ended up with:
42mm - 50/53
[if the 33mm size is "0" and the 48mm size is "100", then the 42mm size is, "62.5"]
That sounds nice. Sufficiently lower than the 33s, which is one of my goals. I then calculated pressures based on proportion/comparison of volume [33mm = 706, 48mm = 1,661, with 42mm's 1,256 being "57.777...."]
I got 52/55 PSI, which ends up being very close to the previous value/ratio/fuzzy math number [all the engineers are going to murder this industrial designer over here
"Hey, guys, I liked and did well in math! It was a while ago, but please put your forks down!"]