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Smart Trainer Calibration: Hot and Cold
The heart of power accuracy lay in calibration.
One of the best features of a smart trainer is their ability to provide power numbers. And when it comes to power, nothing is more important than accuracy.
With a smart trainer, the heart of power accuracy lay in calibration. Saris and CycleOps bike trainers can be calibrated with the Saris App (iOS | Android). This calibration process is especially important with smart trainers that have a tire-to-roller interface, also known as a wheel-on trainer. The Magnus and M2 are an examples of this type of smart trainer.
Since each bike set-up is different, each bike needs to be calibrated with a smart wheel-on trainer to ensure the best possible accuracy. This is because no two bike set-ups are the same as each uses different tires, rims and recommended tire pressures, all of which play a role in dictating the rolling resistance measured by the trainer.
It’s this varied rolling resistance that the roll-down calibration is measuring and accounting for when calculating power readings, or wattage. Since rolling resistance can change from session-to-session, or even within the same ride, we recommend performing a calibration as frequently as you wish to keep your power numbers as accurate as possible.
You may notice that this recommended calibration protocol is for wheel-on smart trainers only. This is because direct drive smart trainers, like the Saris H3, CycleOps H2 and Hammer, do not need to be calibrated as often as wheel-on trainers, as there is no tire-to-roller interface. The direct drive design reduces the variability in rolling resistance from ride-to-ride.
Before you calibrate your wheel-on smart trainer, be sure to do the following:
- Mind the PSI: Inflate your bike tire to the highest recommended PSI listed for your wheel and/or tire. Doing so will help get the best interaction between your tire and the trainer's clutch knob.
- Get a Trainer Tire: The tire you use can impact calibration, which is why we strongly recommend the use of a trainer tire.
- Let the Clutch Knob Do the Work: Make sure the clutch knob is fully engaged with the rear tire (i.e., you hear an audible click, like a gas cap). The clutch knob will compress your tire at least halfway toward the rim. The tire will not pop. This is okay. This level of roller-to-tire engagement prevents slipping during a ride, excess wear on the tire and more accurate readings.
Now you’re ready to calibrate your wheel-on smart trainer. There are two ways to go about this important process:
1) Cold Calibration
Traditionally calibrating a smart trainer is done at the beginning of a ride. This calibration often happens prior to when the trainer and tire are "warmed-up." When performing a calibration before the tire and trainer are warm, the cold calibration will be unable to account for the decrease in rolling resistance from the start of the ride when the equipment is cold to when it’s been warmed-up.
With this variance in equipment temperature, the rider may not be experiencing peak accuracy from their smart trainer. The old way of accounting for this was to ensure that a warm-up was done on the trainer before performing the calibration, and then begin the ride/workout.
2) Hot Calibration
The steps for completing Hot Calibration are the same as the Cold Calibration. A Hot Calibration is simply a second (or third, or fourth calibration...) performed after the rear wheel is warm and the rolling resistance has stabilized.
Since indoor cycling apps will also be trying to send control signals to your trainer, we recommend calibrating with the Saris App before pairing to your training app of choice (ROUVY, Zwift, TrainerRoad, etc.). If you want to perform a Hot Calibration mid-workout or during a virtual ride, remember to pause the training app and then connect to the Saris App.
To perform a calibration with the Saris App, follow these steps: