Very interesting discussion.
my Corolla GLi 2010 consistently gave average of 12km/litre in Islamabad City. My car has 205 Yokohama dB series tyres and I check the tyre pressures on weekly basis. I keep the tyres inflated at 30 lbs. Last week I had a discussion with a friend who also owns the same car. He is using stock tyres and gets the same fuel mileage.
just out of curiosity, I checked the Eco Challenge on my Garmin 2460LT GPS and I found there was something wrong with my fuel consumption. The Eco Challenge gives maximum of 99 points on best driving which includes parameters of braking, acceleration and speed, and based on that, gives an Overall Score.