When purchasing a smart trainer (a bike trainer that works with an app to simulate hills) you can choose a “wheel-on” version or a “direct drive” version. With direct drive, you remove the rear wheel from your bike and put the skewer straight through the trainer and the axle. The cogs for shifting gears in the back are built into the trainer. These tend to be about twice as expensive as the “wheel-on” versions, in which you leave your rear wheel attached to your bike, and seat it in the resistance mechanism just as you would on a traditional trainer.The wheel-on smart trainer might look like a traditional trainer, but it is a different beast. You’ll need to remember a few new tricks.
On most traditional wheel-on trainers, there’s no need to think about braking, because as soon as you stop pedaling, the whole mechanism comes to a halt after a second or two. It’s one of the frustrating things about regular trainers … you never get a chance to coast!However, most smart trainers work differently. They allow for “spin down” so that it’s possible to simulate downhill sections and more accurately apply the algorithms that approximate power metrics. (In fact, you’ll want to learn how to decrease the difficulty setting during a workout if you have your app or program set to keep you at a minimum power output. Sometimes you can get stuck after coasting because the computer program is adjusting to your lack of pedaling and requiring a ridiculous amount of power per pedal stroke to keep maintain the workout parameters despite your low pedal cadence. You’ll have to lower the difficulty briefly until you can start pedaling again.)The reason this is important is that you need to remember not to brake! If you have completed your workout and stop pedaling, you will need to wait a few moments for the wheel to stop spinning. Unlike on the road, the momentum of the flywheel is pushing your wheel around. If you clamp down on the brakes, you will put an incredible amount of pressure on your brake parts and/or your tire tread because the heavy flywheel on the trainer will attempt to keep spinning. It would be like applying the brakes in your car while moving through the automated car wash.
You are saving money getting the wheel-on trainer, and you’ll need to invest some of that savings in an extra beefy tire. Unlike the lightweight, treaded tire you want to use in road training and your race, your trainer tire needs to be heavy and smooth. Rubbing against the metal of the trainer for miles and miles, the smooth tire will minimize friction and the thicker rubber will withstand the heat and stress longer. You can either get a lot of practice changing tires, or you can buy an extra wheel so that you have a dedicated trainer wheel. (It’s must easier to swap out wheels than to swap out the tire repeatedly.)
Unless your tire miraculously stays at the same exact tire pressure all of the time, and you screw down the tension on the trainer to exactly the same resistance, and there are no environmental factors impacting tire pressure or resistance, please run through the recommended calibration exercise before each workout. With a wheel-on smart trainer, your power output is being approximated by mathematical formulas. In order to making your training meaningful, you want that wattage to be as accurate as possible. Since the factors above can dramatically change how much work you are doing to move the trainer flywheel, you want to reduce the variables as much as possible. By performing a “spin-down” at the start of each ride, you give your smart trainer a chance to calibrate to today’s conditions and setup. Most smart trainers come with an app for syncing up the sensors and calibrating the power readings.