A-bike / A-bike Plus / 6" wheeled A-bike Smart

Dual Chain ratios: 14:8 and 35:9

Tyre Size: 15cm/6" diameter x 3.2cm/1"

Crank length: 140mm

Gear inches: 6" x 14 ÷ 8 × 35 ÷ 9 = 40.83"

Metres of development: 0.15m x π x 14 ÷ 8 × 35 ÷ 9 = 3.21m

This means that the bike travels about 3.21 metres per crank rotation.

Gain Ratio: 150mm ÷ 2 ÷ 140mm x 14 ÷ 8 × 35 ÷ 9 = 3.65

A-bike City / 8" wheeled A-bike Smart

Dual Chain ratios: 14:8 and 33:11

Tyre Size: 20cm/8" diameter x 3.2cm/1"

Crank length: 140mm

Gear inches: 8" x 14 ÷ 8 × 33 ÷ 11 = 42"

Metres of development: 0.2m x π x 14 ÷ 8 × 33 ÷ 11 = 3.30m

This means that the bike travels about 3.3 metres per crank rotation.

Gain ratio: 200mm ÷ 2 ÷ 140mm x 14 ÷ 8 × 33 ÷ 11 = 3.75

What is "gear inches"?

http://en.wikipedia.org/wiki/Gear_inches

What is "metres of development"?

http://en.wikipedia.org/wiki/Gear_inches#Calculating_metres_of_development

What is "gain ratio"?

http://www.sheldonbrown.com/gain.html

Information about measuring gears:

http://en.wikipedia.org/wiki/Bicycle_gearing#Measuring_gears

Gear ratios comparison among tiny wheeled folding bikes:

http://www.abikecentral.com/forum/viewtopic.php?f=2&t=1369