Hi Gang
   New  90 Ls400 owner here, just finished my first tank of fuel and recorded 390mi on 17.1 gals of fuel. The cars rpms at 80mph (130kph), stands at 2000.
The car is compleatly stock and I think that really helps the mpg,s. The one tire that could possible improve mpg are the HP varieties that run 35 to 50 psi of pressure. Big wide tires will surely decrease mileage but they look so good.
I think the v8,s do just fine cruising at 15oo rpms and when you need to go faster, thats what your trans is for. Your engine will last longer at lower rpm usage.
                                                                    195,ooo m 305,000 to go
                                                                    PhatGrip