Browse any online cycling forum and you’ll discover two types of people: those who think gear selection in ERG mode doesn’t matter and those who swear by it. ERG mode, for starters, is a mode on smart trainers like the Wahoo Fitness KICKR that will set your trainer’s resistance for you. It helps by adjusting resistance to match Target Power, so you don’t have to worry about doing it yourself.
But if ERG Mode is a feature that helps you reach target power automatically, why is there such an debate? It seems helpful, right? The problem lies with each cyclist’s “realism” and “road feel” preferences — and that’s much too subjective to ultimately answer the questions around ERG Mode.
When you get down to the science of ERG and gear selection, the results are pretty clear. As Shane Miller describes, “momentum” of the flywheel or kinetic energy is a more scientific understanding of what the heck is going on in ERG mode. And the results are pretty clear: momentum makes a big difference when you compare small momentum trainers versus high momentum trainers.
Example: Hill vs Road Momentum
Here are two scenarios using the same wattage and RPM, but with two very different landscapes.
- Flat Road / 330 Watts / 90 RPM
- Big Hill / 330 Watts / 90 RPM
If you stop and adjust your shoe for a few seconds on the flat road, your momentum won’t drastically change. Your momentum is high enough while you’re cruising so that it doesn’t take a whole lot of effort to come back to the handlebars and get back up to speed. Alternatively, if you adjust your shoe while you’re climbing up a hill, you’ll be starting at a much lower speed. It will take considerably more effort and time to get back to where you were before the adjustment.
But it’s not just that; As you pedal up the hill, your pedal stroke will have to be higher and all the way through. Whereas when you’re riding along the flat hill, you’re “tapping” on top of the gear and it’s a much quicker and easier effort.
When choosing a smart trainer, it’s important to consider this factor: how big is the flywheel?
Smaller flywheel trainers will have smaller kinetic energy and smaller momentum and lower inertia. A trainer with high inertia, or high kinetic energy, will help keep you on top of the gear — and this makes a big difference during training.
Deeper analysis of the data shows that the OCA (or Optimal Changing Angle) is different between the two tests. This angle is an indication of where you should install your curing based on the flywheel speed.
Why is this important? You’ll be using different muscles based upon your ride style, so without ERG modulating for you, you may not get the results you want when moving from indoor to outdoor training. If you want to maximize your training for your different workouts, it becomes clear why ERG Mode makes a huge difference.
As Shane Miller explains, “If you’re looking at using a single speed on a KICKR make sure you select the right gear for your training.” You shouldn’t be exercising like you’re training for hills if you’re only training for flat time trials (and vice versa).
For more on Shane Miller’s experiment on ERG Mode and gear selection, check out his video above. Learn More about the KICKR HERE.