to increase top speed do i need a smaller or bigger sprocket and if so,do i need to change them both?

 

You would need a larger front or a smaller rear. A good rule of thumb is that 1 tooth on the front sprocket is equal to 2 1/2- 3 teeth on the back. Dont go to crazy or it may take you forever to reach top speed. The engine only has so much power. No you dont need to change them both. Just remember that a larger sprocket will require a longer chain and a smaller one will require a shorter chain.

 

I am not questioning you but if you go smaller in the back, that would make it quicker off the line but slower at top end correct?

 

No, exactly the opposite. Think of it as leverage ratio. If you had a 10 tooth front sprocket and a 40 tooth rear sprocket the ratio is 4 to 1. A 80 tooth sprocket would be 8 to 1.

8 to 1, rear wheel turns 1 revolution to engines 8 revolutions.

4 to 1, rear wheel turns 1 revolution to engines 4 revolutions.

Bigger rear sprocket gives the engine the advantage, but slower top speed.

Hope this help's.