Why does it feel harder to ride on the trainer than on the road?

To explore the phenomenon of resistance on the trainer versus the road we need to go back to high school physics and talk about Newton’s laws of motion. Newton’s first law, the law of inertia, describes how a body at rest stays at rest, and body in motion stays in motion until acted upon by an unbalanced force. In very basic terms, if you are sitting on the couch, doing nothing, you will not move from the couch until you exert the force necessary to move. Newton’s second law addresses said force describing that the application of a force will change the velocity of an object that the force is acted upon. Mathematically speaking, force equals mass multiplied by acceleration. Thus the large the mass, the larger the force needed to accelerate the given mass. This is why it is hard to ride up your favorite hill post holiday weight gain- thank Newton here, as well as your extra serving of desert. We all know that you have to exert a force (or watt) to move an object, and normally the object we want to move is our bike and body along the open road, this is the application of Newton’s First Law. Let’s take this to the second law that force equals mass times acceleration. On the road we have a lot of mass to move (your bike and your body weight), so there is a lot of force needed to accelerate that mass. However, on the trainer, we don’t actually move the mass of our bikes and body weight anywhere, instead we accelerate the mass on a small flywheel. To make a long explanation short, you need to keep generating forces (watts) in a constant manner to keep accelerating the small mass of the flywheel of the trainer because the acceleration and resistive forces of the trainer are so small. This means a more continuous force is needed to generate the same watts. It all comes back to the small mass of the flywheel versus the bike and body weight that you are normally moving. You may not realize it, but you actually get small micro-breaks when you generate those watts on the road because of the acceleration you gain. On the trainer, you don’t gain the same amount of acceleration because of the small mass of the flywheel and that is why it can feel harder to produce the power.

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