Well 38 x 16 is about 64 gear inches with 27" tires. That works out to about 15 - 24 kph @50 - 80 rpm cadence. That seems like a reasonable starting point for the average recreational rider. Low enough for short hills and a moderate headwind, and high enough for comfortable flat land cruising. But might be frustrating if you want to take advantage of a tailwind. For that 78 gear inches (26 kph @ 70 rpm) is good on my comfort bike.
As far a lowest goes, The new (2021) Giant Simple One cruiser uses 57 gear inches. I've never ridden a beach cruiser, But I assume ridding in sand (the damp part near the water) needs lower gears then a comfort or hybrid bike.
Last edited by xroadcharlie; 02-27-21 at 05:58 PM.