UCI regulations govern the maximum distance that the cycle can travel in one complete turn of the pedals. e.g. Age 10 max progressive metres is 5.4 mts. The formula to calculate progressive is ( Number of chainring teeth / Number of sprocket teeth ) x Outside circumference of wheel. With this calculator you can quickly calculate the progressive metres then if required alter the three variables of tyre, chainring and sprocket size to obtain the optimum progressive metres for the age of the rid