>>1407579in that case 30 kph should be farely easy on your bike
and if you want to go 40 kph 53x14 should be fine
or 48x13 if your willing to slightly exceed 100 rpm
46x13 will only just work
of note however is that 6 speed free hubs with a 13 tooth gear are rare
and 60 tooth chain rings are more for velodrome bike's
where as chain rings closer to 50 teeth are in common use on older style road bikes
