Okay so I have a Pilot Road 2 on the ream rim. About 5 months ago, while I was riding, it randomly went flat. I got to the nearest gas station and filled it up. Had no issues for 3 months. Then all of a sudden one day I was riding on the freeway, it went flat out of nowhere. I went to the nearest gas station and filled it up, then road again and let it sit for about 5 hours. No air had leaked out. Then I got back on the freeway and after a couple minutes, it went completely flat out of nowhere.

I've had the rim+wheel off the bike for about a month now. I had it filled to about 60-65psi for a whole month. I did all the normal tests of spraying it with soapy water and even dunked the whole wheel +rim in a tub filled with water. There is not 1 single tiny air bubble anywhere, and no air leaked out for that whole month.

Wtf is going on here? How can I figure out why it was going flat out of nowhere at speed?

Sounds like it might be a fooked valve stem. If not then it has to be the bead, I mean it's leaking from some where...Did you make sure to fill it with summer air and get that winter fall air out? That will cause a loss of PSI since the colder winter air is...much more.....dense.



Do I....sound like. Dribble...yeT?

Centrifugal force due to road speed at the rear wheel might be placing load on the bead and causing the seal between the tyre and the rim to leak - very unusual situation though.
Refit the tyre without any lube on the bead and put a little gasket goop on instead and see if its still leaking at speed. Easy to clean off if it doesnt work but man what a pain in the azz.

The high pressure at test will actually hide a bad bead due to the force eggzerted against the rim. I vote for bad stem seal. Do you use a sealed cap?
Mark the tyre so you can see if it is spinning on the rim. The factory light spot dot should suffice as a gauge. I did replace my air and try to use a high elevation bottled air from Denver when available. It lightens the wheel and feels just like switching to carbon wheels. If you can't source it Ill give you the contact. Nitrous Oxide is even better and is easy and fun to check for leaks.

would a valve stem leak be slow at speed? Because the loss of tyre pressure is ridiculously fast.

It only took like 10seconds for it to go flat from full. That's what it seemed like anyways. Was perfectly fine one sec and then all of a sudden shit was flat and I had no control of the rear

Sucks because that tyre is almost brand new with a shitload of life left on it.

Take it up to 65-70 psi to set the bead,then reduce to normal pressure.I had a similar problem with a road 3 and this fixed it .
I would also be concerned for your rear wheel bearings if you have immersed the whole wheel.