The connecting rod of 4-stroke is subjected to an Iberia whip loading which occur due to the mass of piston and high speed of rotation , swinging about piston hinged point.
In Two stroke engine the whip loading is less,which is due to less due to low speed of rotation of con rod.
Moreover,there is a reversal of stress due to inertia load between the inlet and the exhaust stroke of the engine.
Hence,we need to reduce the inertia.For this we need to reduce the weight of the connecting rod.
Reducing the weight of connecting rod without the compensating the strength of the con rod ,the connecting rod of the engine is of I – section.
The I – section has greater strength than the round section without compensating it’s strength.
HENCE TO REDUCE THE INERTIA WE 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.