Hundreds of different combinations of ratios exist. You must understand that going from a larger driven sprocket ratio to a smaller sprocket may enhance your low-speed acceleration, but your engine must rev higher. In turn, while your acceleration off the line may improve, your high-speed acceleration may decline. It's all a matter of trade-offs, since your engine puts out a finite amount of horsepower.
You have to fine tune the kart to the track and engine conditions. These conditions can vary greatly. Some variables are the weather, the composition of the track surface and how the composition of your tires reacts with the surface. Engine conditions vary with the weather. On a high humidity day, the engine intakes moisture, affecting its performance. On dry days, the engine intakes dry air, which also affects its performance. To compensate for all the variables, you have to experiment with different ratios to determine the best ratio to use on race day. The final selected ratio should provide excellent acceleration off the line, as well as good acceleration at high speeds.
The racing team of Ronan Quinn uses a computer program to help select sprocket ratios. After a few trial runs on the track, data such as lap time, maximum engine rpm, condition of track, and size of tires is entered into the computer. The sprocket sizes used on each run is entered as well. The program analyzes the data and provides a detailed report by displaying a visual graph of the most efficient trial runs.