Change of sprocket size

Hi, I have a 2003 ZX6RR which has an inaccurrate speedo. I checked with Kawasaki and they said I should have a 43tooth rear sprocket but I have a 40 tooth - I haven't checked the front as it can't be seen without some work. If I put a 43 tooth sprocket onm, what differences will it make?

Thanks
Ben

According to my sources the front sprocket on your zx6rr is 15 teeth and the rear is 40 teeth from the factory. Of course I am getting information from a source in the U.S. but I doubt the Aussie version would be different. Adding 3 teeth to the rear would decrease your top speed and increase your rear wheel torque. A shot and a brew help all troubleshooting.