Driven Racing EVO TECH front sprocket for fits and compatible with Honda Grom and Monkey 125cc with 428 chain. Driven fits and compatible with Honda Grom and Monkey 125 front sprockets are available in 13t, 14t and 15t options. The stock front sprocket size on the fits and compatible with Honda Grom is 15 tooth. You can go down to 13t or14t to increase your low end acceleration. A few rules regarding gear ratios for sprockets are as follows: Drop teeth on front/add teeth to rear = increased torque, increased acceleration, wheelies, racetracks with short straights Add tooth on front/reduce teeth on rear = increased top end speed, open road cruising, lowers RPMs, better gas mileage, tracks with long straights 1 down on the front is like adding 3 teeth on the rear The bigger the rear sprocket, the lower the gearing and the faster the acceleration