Dimoby 40 ad 50 serie Mobys came in three flavours: 20, 25, 30mph rating
12 x 44 = 3.67 (20mph Dimoby)
11 x 48 = 4.36 (25mph Dimoby)
13 x 52 = 4.00 (30mph Dimoby)
Variator Mobys only came in one flavour: 30mph
11 x 52 = 4.73 (30mph Variator)
Make note that the drive gears are matched to the hardware behind the driven pulley, so a 11 gear needs a 11 gear engagement arm, a 12 gear needs a 12 gear engagement arm, and a 13 gear needs a 13 gear engagement arm. On initial install youmay think "bullshyte" however the engagement arm will fail with zero notice or warning and you will hear "the machine gun sound" and your Moby will go no further under power of the motor. (edited)