Cargo Bikes: Gears and Gearing - Intro
Most cargo bikes come with around 24 - 27 gears, unless they are from Holland. If you are building your own and which to choose gears to suite then perhaps follow the below advice.
Cargo Bikes: Gears and Gearing - Shopping and General Use
Carrying extra weight will mean that you will need a greater gear range. I struggled buy with a gear range of 300% for a number of months pulling 35kg up fairly steep hills.
300% can be provided by a 1 x 9 setup, that is 1 chain ring at the front and an 11 - 34 cassette at the rear.
On flat ground you might choose a 42 tooth chain wheel up front, but for hillier areas operhaps a 32 tooth chain ring might be better.
Cargo Bikes: Gears and Gearing - Kids and other Heavy Loads
A 3 year old and 5 year old will weigh about 30 - 40 kg depending on what you are feeding them, this really changes things, and 300% range will no longer cut the mustard.
A 22 tooth chain ring will now probably be required up front which combined with a 34 tooth sprocket at the rear will give a good low gear, for lugging heavy loads up fairly steep hills.
You highest gear may well be determined by you fitness and and your desired top speed, but I have found that a 32 tooth with the 11 sproket at the rear ios "stiff" enough for my liking, and I don't want to go that fast.
So in the end I have settled on a gear range of 450%
Cargo Bikes: Gears and Gearing - Conclusion
To work out your gear range, you can use this gear range calculator spread sheet.
Many European cargo bikes are sold with gears giving a range of just 250%, and for holland and London, this is fine. If you live in hillier areas, then you will be needing at least a 400% range, some high end hub gears can offer close to this range, but for the price savvy it will be derailleur gearing. . . or get off and push!