Sprint ST FAQ's - Chain and Sprockets

Q: How do I change my sprockets ?

Answer:

Front

Tools Required: 36mm sprocket, breaker bar (or impact wrench), torque wrench

  1. 1 - Remove sprocket cover
  2. 2 - Loosen chain
  3. 3 - Bend down tabs on securing washer. Leave bike in gear - have second person hold front and rear brakes. Remove nut - requires 36mm socket (helps to grunt a lot - some have even required use of air tools to remove the nut)
  4. 4 - Remove old sprocket
  5. 5 - Replace with new sprocket
  6. 6 - Torque to 132Nm
  7. 7 - Bend securing tabs back up

If doing rear sprocket as well, do it now.

Q: What is stock gearing on my ST ?

Answer:

1999 - 18 / 43

2000 and up - 19 / 43

Q: What performance change can I expect by changing sprocket size

18/43 gives good acceleration in 1st and 2nd, yet gives a low motor speed when cruising (under 5k @80). 17/43 will give better acceleration in 1st and 2nd, yet will make your top end looking for shift for highway use. 19/43 will give you great touring speeds, but may leave you looking for more on the low side.
A purely theoretical examination of the performance would suggest the following statistics. The variance in the acceleration times occurs when a gear change occurs at the top of the acceleration window (i.e. 60 or 100).

Front Back Ratio 0-60 0-100 top
19 43 2.26 4.06 8.45 166*
19 45 2.37 3.61 8.44 158*
18 43 2.39 3.59 8.41 157
18 45 2.50 3.66 8.23 150
17 43 2.53 3.64 8.20 149
17 45 2.65 3.54 8.27 142

* Speed at max revs. Wind resistance limits actual max to ca. 157 mph.

 
Thanks to Keith Tynan for information