I've seen 10 km, but I usually don't go below 20 km. And if there is a gas station handy, I pull over after the yellow light comes on at 50 km. My vehicles have all been very linear down to 20 km remaining or so.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue