View my fuel log 2013 Mirage 1.0 manual: 47.5 mpg (US) ... 20.2 km/L ... 5.0 L/100 km ... 57.0 mpg (Imp)
I'm seriously wondering if not airing the tires up to 44PSI/4.4 bar (I think) is holding my car's mileage back.
Sure it is. If you're OK with the harsher ride, and don't drive on gravel/broken pavement much, I'd go for it.
Monitor tread depth for unusual wear. I've gotten away with higher than spec tire pressure in all my cars without adverse wear issues, but some cars/tires may wear in the center from high pressure.
FYI, a comparison of changing tire pressure on rolling resistance:
Experiment: coast down distances (rolling resistance) @ various tire pressures
40 seems to be the best compromise between comfort and economy. You don't really gain a terrible amount more roll-out but you do get a cement truck ride.
Came very close though a while ago
3.3L/100km --> 30.3km/L
View my fuel log 2015 Space-Star 1.0 manual: 48.8 mpg (US) ... 20.7 km/L ... 4.8 L/100 km ... 58.6 mpg (Imp)
I just did a 160 km round trip this afternoon and saw the same result (72 mpg US) in my 1.0L Chevrolet Metro (Suzuki Swift). Max posted speed limit of 80 km/h = 50 mph, light traffic. Includes going through 2 small towns with traffic & multiple stop lights. Hot, dry, conditions (28 C / 83 F). Stronger tail wind on the return trip than the head wind on the first leg.
But my Metro is extensively modified for better efficiency: