[Cycling] Gearing Ratio

i'm quite new to bmx riding , what exactly is the gearing ratio needed for??

the gearing is measured in inches. its the number of inches you will travel with one complete revolution of the cranks. but you want a gearing which suits you. obviuosly you want the biggest gearing you can push...but if it is too big you wont be able to push it....trying to find the right gearing can be a real pain.

you take the number of teeth on your chainring and divide it by the number of teeth on your freewheel, that gives you your gear ratio. For example, if your front sprocket is a 45 tooth, and your rear sprocket is a 16 tooth, then your gear ratio would be 2.8125 (45 divided by 16 = 2.8125). You then take that number (in this case 2.8125) and multiply it by 20 (the diameter of a BMX wheel). 2.8125 x 20 = 56.25 (the gear size)

so... whats a good way to tell what your ratio should be??

getting a pal to time your sprints over a set distance

how long should i test for good results?? like 100metres?

100metres is a good distance , just keep a record see what works best