I've managed a lifetime 50+ mpg average since my car was new (coming up on 35K miles). I've done this with 15" wheels/tires on my car almost since day 1.
I only do basic hyper-miling stuff (coasting up to red lights, minimize AC usage, limiting freeway speed to around 60mph). I don't have any mileage "mods" other than keeping my tires at their maximum sidewall pressure.
Now that we're into winter-blended fuels and cooler temperatures, maintaining 50+ is more challenging...and almost impossible for me when temps stay below 30 degrees. I need to have lots of 50+ mpg fill-ups in the summer to counter-balance my sub-50 tanks in the winter. This is why I am starting to play around with partially blocking the grill and using a warm air intake in the winter. One winter advantage I have is that my car is garaged and I use an engine block heater.
I would really like to ride along with someone getting 60+ mpg on a regular basis. I don't know how they do it. I think I would have to find a perfectly flat road 500 miles long and drive 45mph without stopping to get those numbers.
View my fuel log 2015 Mirage ES 1.2 manual: 51.5 mpg (US) ... 21.9 km/L ... 4.6 L/100 km ... 61.8 mpg (Imp)