i found a difference of one gear between my stigmata gravel bike with 30c tires and six13 road bike with 25c tires
i.e. going up a hill i'd typically need one gear lower/easier on the stigmata
with bigger tires (35c) on the stigmata, it might go up to 2 gears difference.
same size tires on both bikes, the difference was nearly unnoticeable