Bicycle

Gear ratio

Pure gain ratio according to Sheldon Brown Calculated as: wheel radius / crank length * front / rear T

Gearing and cadence

Bike modelGearingPure gain ratio
Surly Steamroller49/17T 700(680mm) wheel 170 crank5.76
Leader 72546/17T 700(680mm) wheel 165 crank5.57
Cinelli Vigorelli48/17T 700(680mm) wheel 165 crank5.81

Cadence for a fixed is linear to the gearing.
(1056 / 1.609344 * rear * speed) / ( front * 26.28 * PI)
26.28 is constant for wheel 700x23/23-622

SpeedCadence
49/17T48/17T46/17T49/15T49/14T49/13T
15 41 42 44 36 34 32
20 55 56 59 49 45 42
25 69 70 73 61 57 53
30 83 84 88 73 68 63
35 97 99 103 85 79 74
40 110 113 117 97 91 84
45 124 127 132 109 102 95
50 138 141 147 121 114 105

Recommended CT

Recommended CT length according to cyclecomponents.com

Length of leg in mm (B)

racerB x 0.883 - 180 = CT
MTBB x 0.883 - 280 = CT

B = 810mm

racer715 - 180 = 535mm = 21"
MTB715 - 280 = 435mm = 17"

33T - 18T comp

29" wheel. crank 175mm-180mm4.3
26" wheel. crank 175mm 4.3 with 33T front = 16T back