changing front tooth ratio has bigger effect for 1 tooth at time, 17f to 43 rear = 2,52 to one ratio, 18f to 43 rear = 2.38 , doing rear 17f to 42 rear = 2.47 17f to 41 rear = 2.411 to one, but changing front sprocket especially down massively increases forces on chain- much tighter curve around sprocket