Pulley/Bealt Calculation and why 15teeth to 36teeth is often used?

I’m a engineering student and building my longboard ,so far I came across the use of a timing belt . Now i want to use a Belt too for several reasons,but as a inquisitive student i want to know the reason why everybody uses 15 teeth and 36 teeth pulleys . I’m in early stage and my only requirements are a speed at 30km/h and a wheel size by 83mm and a range at 15km. So if i want to use a bigger wheel which things i have to change.

Do the math! :smile: Do you have a motor and battery in mind? If so you should be able to do the math and figure out the gearing ratio.

If you didn’t then you need them, otherwise too many variables hint hint