For a 5th gear swap, many are external to the case, found underneath a stamped steel cover on the end of the gearbox. It's literally a half hour job for some cars. Not sure about the Micra, but I'd be surprised if it was any different.
Taller tires would help too. Then lower the suspension to cancel the lift. Win win!
One thing you have to be careful of though: taller tires are good for gearing, but wider tires are bad for aero (as are most aftermarket open spoke wheels). Low rolling resistance is also usually not a goal of performance tires.
Originally Posted by
Daox
You think you could have done even better?
Sure, with the mods in place 100% of the time it would have been better.
A more advanced driving technique you can use with a manual but not an automatic: coasting with the engine off. I didn't do this because the Micra's fuel economy display doesn't update properly when the engine's not running, and it would have thrown the calibration way off. But it probably would have improved the numbers by another 5% or so.
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View my fuel log 2015 Micra S manual: 5.0 L/100 km ... 56.5 mpg (Imp) ... 20.0 km/L ... 47.0 mpg (US) ...