Ugh unknown China cheapo brand but nonetheless should not cause such drastic drop in fuel consumption. I suggest you recheck the tire pressure yourself at the fuel station then observe again for several rounds of full tank (not just simply fill up rm50). Measure properly by resetting the trip meter to zero everytime you pump full then drive until fuel warning light turn on then see how far you travel. My suspicion is tire pressure too low and you didn't measure properly but just by feel which is inaccurate.

Btw what car do you drive, what tire size and how much did you pay for that China cheapo tires??

Wah really damn cheap, scary cheap almost like used tire price. I personally would rather buy used tires but good ones than these unknown cheapo but most people don't know how to check hence not an option for them. Anyway understandable in this difficult times, many loose jobs or get pay cuts so need to try save as much as possible. Just be mindful when driving coz usually these cheapo tires have horrendous grip especially in the wet. Drive safe.

No lah, most car std recommended pressure is around 190-230. My Evo and Swift only 220 front and 200 rear. My heavy Mark X only 230-240 max. 260-280 is already too hard for most cars unless you like harsh uncomfortable ride. Too high pressure like that also lose grip and too nervous in the wet. Persona is also a light car, no need such high pressures, at most should be just 220-230.