10W-30 is fuel effiecient tested on cold climates like US. because its lighter compared to 40. if you planned to change oil let say every 3-4 mos. ok sya gamitin sa tignin ko pero if going for long change intervals mas ok yung heavier oil like 40-50.

reason for this is climate(sobrang init dito sa pinas) and traffic. an oil weight at 30 is too thin to withstand too much heavy traffic on a hot climate like philippines, you'll get the engine exhuasted.

ganito yon in short:

QUALIFYING: 0W,5W,10W-20,30 (yan pwede kasi 1/few laps lang) doesnt required long race laps

RACE: they opt for thicker viscosity like 20W-50,60 (30-60laps of full racing)