Lexus specs put the IS-F at 16 City, 23 Highway.

http://www.lexus.com/models/ISF/deta...fications.html

Interestingly, that is almost exactly what my old IS300 was rated at (17/23), with much less power than an IS-F. I suspect that is because of the IS-F's 8-speed transmission, but an interesting question comes up as to how often you will actually USE 7th or 8th gear, particularly in urban areas.

 

The answer to that is all the time. In city driving the tranny will get you into the best gear possible to optimize fuel efficiency. Even if you're only going a smooth 40 mph, it will eventually find 7th and 8th and keep the rpm's lower. Of course, that is just regular driving in Automatic mode and not driving like the car was meant to be.

 

7th and 8th at only 40 MPH probably means a lugging engine, though, if the transmission's ECU is working properly, it will automatically downshift on upgrades or with significant pedal pressure, unless you use the paddles and manual Sport-Shift in that range.

I reviewed an IS-F in the spring of 2008, and, I think, in full auto mode, I got the gearbox up to 7th and 8th only once.....on a relatively long stretch of straight 4-lane highway. Under most normal driving, and especially under acceleration, it was hard to get it past 6th.

On a separate note, I almost lost a couple of teeth (and vertebrae) with that car on rough roads and frost heaves....its factory suspension, particularly the rear suspension, was almost race-car stiff, and made the rear end jump up and down like a porpoise over bumps. Early-production IS-F's were noted for their stiff underpinnings. The only other 4-door sedan I've ever driven like that was the last-generation Mitsubishi Evo (the Subaru STi and BMW M3 were close, but not quite as stiff)