harrier

My daughter has an Electra Hawaii 1 20" cruiser. It is a single speed coaster brake model with a 40 tooth front chainring and 20 tooth rear. The cranks are 140mm.

I bought a 20"x1.5" rear wheel with 7-speed Shimano Nexus hub and need to figure out whether I should use a 20-tooth cog on the Shimano hub.

She does fine with the single speed, but has to dismount for hills. It also gets a bit ahead of her on downhills. I would like to give her 2 or 3 more high gears but also give her more options on the low end (without being ridiculous). She loves riding but is mad when she has to walk the bike.

I really appreciate the help.

fietsbob

Using : https://sheldonbrown.com/gears/internal.html
I get this , inputing a slightly wider tire.

23.6/27.7/31.5/36.9/42.8/49.9/57.7
57 inch is a decent Gear size for cruising along, modest tailwind.
Try out different cog and chainring choices and see what you get.

4 of 7 is direct gear, sprocket turning the hub-shell as if still a 1 speed.