Hi John,

There's no simple answer to that as there are so many variables at play, including the gearing in the gearboxes, etc. Traditional automatic gearboxes using torque convertors certainly made cars less efficient as there is slip in them, but newer versions of those, and dual-clutch gearboxes, are better and sometimes can lead to better economy than the equivalent manual on an overall test cycle. Nonetheless, an automatic gearbox is likely to be heavier, which will also increase fuel consumption.