If you want to go faster you need to go lighter! This is a generalisation but in the vast majority of cases it is true. Triathlon is a race of three parts, on both the bike and run lowering your weight will make significant improvements to your race times.
If you cast your mind back to your science lessons, the greater the mass (weight) the greater the force required to accelerate (move) it. Sorry if you have just eaten that big bar of chocolate but it’s as simple as that. This is why you spent a fortune on that lightweight bike frame, or covet those latest carbon bits and pieces.
Read more here.