New tyres.

[gone-ot]

Originally Posted by JockoT

My car takes 175/65/14's too. With the difference in tread depth between new tyres (8mm on these ones) to 2mm before changing them, this is a difference of 12 mm in diameter (disregarding tyre distortion).

Which is roughly about 3%, from Michelin™ specs. Per their revolutions per mile values, the rolling-diameters compute to be about 97% of the unloaded-diameters.

[JockoT]

I would imagine that is the same for a worn tyre as a new tyre, so should balance out.

[JockoT]

Filled the tank up today, the first complete top up since having the new tyres fitted. Figures were a bit disappointing, but not as bad as they might have been. 55.7 mpg UK - 46 mpg US - 5.11 L/100km.