The RX 400h also gets specific 18-inch wheels. The wheels are 7 inches wide and the tires are designed to provide grip in corners rather than offer low levels of rolling resistance. This says a lot about the intent of the RX 400h. Lexus could have improved fuel efficiency further with hard, low-grip tires, but chose to enhance handling instead.

The RX 400h uses the fourth generation of Toyota's hybrid system, which it calls Hybrid Synergy Drive, and each generation has been faster and less expensive than the previous. Three electric motors draw on 30 modules of nickel metal-hydride (Ni-MH) batteries. Clever engineering has resulted in efficient packaging of the batteries, which are split into three groups housed largely under the rear seats.

The hybrid powertrain adds just 300 pounds to the curb weight. That's not an insignificant amount of weight, but it's an impressive engineering achievement, and most of the weight is mounted low in the vehicle. Lexus increased the rigidity of the chassis to manage the additional mass. The Lexus RX and Toyota Highlander models are built on the same platform (with modifications) as the Toyota Camry and Lexus ES 330 sedans.