sprocket changing for motorcycles?

Question

I'm just curious how much of a change you can make on a bike just from sprocket change.
Say a 04 zx6r.. if you change the gearing like -2/+4 (just an example) could you turn the bike into a 9second quarter mile bike? Or low 10s?
Or is there a limit to the amount of "torque" you'd be gaining from this?

Even if it meant making a bike that can only go 120 or so.. I didn't know if in return you could make a bike that would accelerate extremely fast.

Anyone know?

Answer 1

Theoretically, there is no limit. Practically, however, there is. There is limited room for for some sprocket changes, you can only fit so big a sprocket with the chain to clear hard parts of the bike. Too small a sprocket on the front and the engine won't have enough low RPM torque to even get the bike moving.



While you can move the final gearing, you cannot change the transmission gear ratios. Move the final gearing too far and you will mismatch the transmission and make the bike essentially unrideable.



So, yes, you can "tune" a chain drive bike to accelerate faster at the expense of some top speed or you can move it the other way to allow somewhat higher top speed at the expense of some acceleration. But, there are practical limits to how far you can move those sweet spots.

Answer 2

Guessing that you wish to make the front sprocket 2 teeth smaller and the rear 4 teeth larger which will give you lower gearing and help somewhat with acceleration but to a very moot point because you would need to shift sooner to the next higher gear.

Might get you in the low to mid 10s as long as you are doing second gear launches, as first would be fairing low.

Answer 3

Yes you can lower the final drive ratio within reasonable limits. How fast off the mark that would make any bike also depends on various friction points - clutch and tyre/surface - and the weight of the rider (Physics 101: F=MA)

Answer 4

Traction is probably your biggest limiting factor -- increasing torque is easy keeping the tire hooked up to the track is a bigger problem.