i've always changed the front and back on all my bikes , on the s1 -1 front +1 rear , and there's no prob with the speedo as it runs of the back wheel, felt the s1 lacked a lot of low end grunt this helped it for me ,also let me get a better feel for the power delivery , now i.m running with a pcv and new exhaust i'll prob change the back sprocket to standard again . tbh i dont think u need to change any of the sprockets you just need to learn how the s1 rides and where all that power is and how to release it , try running with traction control of with warn tyres then you'll feel the real power thats on tap , its a differant bike again [MEGA POWER ] lol try it!!! remember make sure ur tyres are warm !!roads aswell !!