First, I researched. I looked at Amazon’s top-rated products and their user reviews. Then I consulted Bicycling magazine, Gear Junkie, Bike Radar, Outside, and the occasional bit by Lennard Zinn via Velonews. I also found some worthwhile discussions at Bike Forums. Then I spoke with four experts, Ramona Marks, Scott Karoly, Cari Z, and Alison Tetrick, riders from all across the spectrum, who tour, repair, and race.
It’s both surprising, and not, if you think about it. The way I’ve usually seen it happen is first the rear tire goes flat, then the front one. My theory is that both tires went through the same pile of glass/thorns/metal bits and they both picked up junk. the reason for the flat occurring on the back first is because there’s more weight on that tire, so the offending article works its way through the tread more quickly.
Basically, you’re stuck with toggling between systems for the advantage of a few pumps, and it doesn’t seem worth it. In the original iteration of this guide, I tested 12 pumps and inflated three different tires completely full to their psi rating, and measured how many pumps it took. Yasuda did similarly for his revamped full-length exploration. That’s 36 tires, and I can guarantee there is no difference between 50 pumps and 100—it’s all terrible.
Modern bottom brackets use a sealed bearing type construction that keeps water and debris locked out, so they seldom go wrong. Maintenance is impossible so they need replacing when they do wear out. Older style cup bottom brackets need to be re-greased every now and again, and occasionally will need to have their bearings replaced. There are a lot more teeth on the chainring cogs than those on the rear cassette, so need changing less regularly. Cranks usually a solid one piece construction so there is not much to go wrong.