Gearing and Tyre Information

Basic gearing information plus rim and tyre considerations.

Gearing
Ratios

This is an extract from a full ratio table with only the sprocket sizes able to be used on the 650.

13 and 14 tooth sprockets seem a little small but they are available.
The 39 and 43 tooth rear sprockets may raise gearing too high.

Sprocket
Sizes

1 - JT Sprockets list 13, 14, 15, 16, 17 tooth front and 43, 44, 45, 47, 49 tooth rear sprockets.
2 - SuperLite Sprockets list 13, 14, 15, 16 front and 43, 45, 47 tooth rear sprockets.

Metric
Calcs

Wheel revolutions per minute
EU Tire Circumference (mm)
Speed in KMH

RPM / Primary Drive Ratio * Gear Ratio / Final Drive Ratio
( Width / Aspect Ratio / 100 + Rim Size / 2 ) * 2 * PI
Wheel Revolutions per minute * Tire Circumference * 60 / 1000

Imperial
Calcs

US Tire Circumference (inches)
Speed in MPH

( Width / 25.4 * Aspect Ratio / 100 + Rim Size / 2 ) * 2 * PI
Wheel Revolutions per minute * Tire Circumference * 60 / 63360

Tyre
Calcs

The gearing calculators on line use the calculations above to determine the wheel circumference
The actual circumference specified by manufacturers can be different to the calculated value.

Mfr

Manufacturer

Model

Size

Circumference

Diameter

Height

% Change

Info

Continental

TKC 80

120/90-17

77 ins

24.5 ins

12.25 ins

+1.2%

TKC 80

130/80-17

76.1 ins

24.2 ins

12.1 ins

TKC 80

140/80-17

78 ins

24.8 ins

12.4 ins

+2.5%

TKC 80

120/90-18

80 ins

25.5 ins

12.75 ins

+5.4%

TKC 80

140/80-18

81 ins

25.8 ins

12.9 ins

+6.6%

% Change is % change over STD 650GS Tyre size to gauge effect on speedo.

Tyre
Diameter

There is another figure for tyres, it is "Centrifugal Radius" which gives a guide to any increase in size when a tyre is spinning. It can be expressed as a ratio. The ratio for road tyres is normally considered 1:1. Continental provide the figure for the TKC80 which suggest there may be up to 20mm increase in diameter on the TKC80. This should be taken into account for tyre clearances.

Rim
Info

An 18" rear wheel can improve ground clearance and open choices on tyre selection. When fitting the larger rim a narrower rim width of 2.5" is used. The 2.5" rim limits tyre size to 12/90 width tyres.

Husky
TR650

The info above can also be used for the Husqvarna Terra along with the calculator pages. The ABS Terra has 17" rear wheel while the non ABS has an 18" wheel. Sprockets are confirmed the same.