CONSTANT GEAR RATIO TABLES

The following table can be used to aid with gearing at the track.  Since tyre sizes (circumferences) vary, this table aids in maintaining a desired constant gear ratio to the track when changing rear tyres.

EXAMPLE :-

Old rear tyres measure 860mm in circumference and new tyres measure 890mm.  Rear gear is 75 teeth.  Read across the line with the 75 gear to the column headed 860.  The ratio is 11.47.  Now read down the column headed 890 until you find a number nearest to 11.47.  In this example it is 11.41.  Now read left across the line to the Gear column to find the number.  In this example it is 78.  Therefore a new rear gear of 78 teeth is required to maintain a constant gear ratio to the track with the new rear tyres.

 
Rear Gear 840 850 860 870 880 890 900 910 920 930 940
67 12.54 12.69 12.84 12.99 13.13 13.28 13.43 13.58 13.73 13.88 14.03
68 12.35 12.50 12.65 12.79 12.94 13.09 13.24 13.38 13.53 13.68 13.82
69 12.17 12.32 12.46 12.61 12.75 12.90 1304 13.19 13.33 13.48 13.62
70 12.00 12.14 12.29 12.43 12.57 12.71 12.86 13.00 13.14 13.29 13.43
71 11.83 11.97 12.11 12.25 12.39 12.54 12.68 12.82 12.96 13.10 13.24
72 11.67 11.81 11.94 12.08 12.22 12.36 12.50 12.64 12.78 12.92 13.06
73 11.51 11.64 11.78 11.92 12.05 12.19 12.33 12.47 12.60 12.74 12.88
74 11.35 11.49 11.62 11.76 11.89 12.03 12.16 12.30 12.43 12.57 12.70
75 11.20 11.33 11.47 11.60 11.73 11.87 12.00 12.13 12.27 12.40 12.53
76 11.05 11.18 11.32 11.45 11.58 11.71 11.84 11.97 12.11 12.24 12.37
77 10.91 11.04 11.17 11.30 11.43 11.56 11.69 11.82 11.95 12.08 12.21
78 10.77 10.90 11.03 11.15 11.28 11.41 11.54 11.67 11.79 11.92 12.05
79 10.63 10.76 10.89 11.01 11.14 11.27 11.39 11.52 11.65 11.77 11.90
80 10.50 10.63 10.75 10.88 11.00 11.13 11.25 11.38 11.50 11.63 11.75
81 10.37 10.49 10.62 10.74 10.86 10.99 11.11 11.23 11.36 11.48 11.60
82 10.24 10.37 10.49 10.61 10.73 10.85 10.98 11.10 11.22 11.34 11.46
83 10.12 10.24 10.36 10.48 10.60 10.72 10.84 10.96 11.08 11.20 11.33
84 10.00 10.12 10.24 10.36 10.48 10.60 10.71 10.83 10.95 11.07 11.19
85 9.88 10.00 10.12 10.24 10.35 10.47 10.59 10.71 10.82 10.94 11.06
86 9.77 9.88 10.00 10.12 10.23 10.35 10.47 10.58 10.70 10.81 10.93
87 9.66 9.77 9.89 10.00 10.11 10.23 10.34 10.46 10.57 10.69 10.80
88 9.55 9.66 9.77 9.89 10.00 10.11 10.23 10.34 10.46 10.57 10.68
89 9.44 9.55 9.66 9.78 9.89 10.00 10.11 10.22 10.34 10.45 10.56
90 9.33 9.44 9.56 9.67 9.78 9.89 10.00 10.11 10.22 10.33 10.44