THE CON-ROD OF 4-STROKE ENGINE IS SUBJECTED TO AN INERTIA WHIP LOADING DUE TO MASS OF THE PISTON SWINGING ABOUT THE PISTON AND HIGH SPEED OF ROTATION. IN 2 STOKE ENGINE THIS WHIP LOADING IS LESS DUE TO LOW SPEED OF ROTATION.
MOREOVER, THERE IS A REVERSAL OF STRESS DUE TO INERTIA LOAD BETWEEN EXHAUST AND INLET STROKE. HENCE TO REDUCE THIS INERTIA WE HAS TO REDUCE THE WEIGHT OF THE CON-ROD WITHOUT COMPENSATING THE STRENGTH OF THE CON-ROD. THE I-SECTION HAS GREATER STRENGTH THAN THE ROUND SECTION WITHOUT COMPENSATING STRENGTH.