Where can I find out info on how much a sprocket changes the speedo?

I need to take the info I find to court. I got two tickets with in two miles on my buddies 600 GSXR with a Vortex sprocket on it. Both where for 15miles over.

I already have a service ticket open on it at my job. The Service manager is going to write how much it was off by. I just need to find that info out. I also need to know the size of the sprocket that would make it 20mph off.


Thank You guys!