How is Strava distance calculated from a TR workout?

I sync my TR workouts to Strava and I see a distance calculation once it is uploaded.

On my 2018 Kickr I turned on “Erg mode speed simulation” as I understand it better associates speed with the power and flywheel.

Does anyone know if the Strava distance calculation is accurate and/or how this is derived from the uploaded data?


It is highly highly varied and inaccurate but your trainer sends a “speed” variable to TR/Strava.

I had the same workout 4 days in a row (Traditional Base). When synced to Strava it came up with 4 different distances, one of which was almost 2 miles difference. Just playing around it seams like cadence and which gear you’re in affects the overall distance when synced to Strava. I’m using a Kickr Snap.

The “Erg Mode Speed Simulation” is intended to deliver a speed measurement that is based on power and not flywheel speed, but it is only supposed to be for head units, and does not affect Zwift or TR or anything that is only using power.

So no it seem like an even greater mystery to me.

TR does not any distance measurements, so is Strava just using the speed + time = distance from inside each workout to calculate distance? I guess the is accurate enough assuming the TR speed calculation is accurate?


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TR doesn’t actually calculate any speed data from the KICKR, since the trainer sends us power and speed data directly for the device - we just record it. The way your KICKR calculates speed is based off of the trainer’s flywheel speed, which can be affected by your gearing, cadence, and the resistance level of the trainer.

I can shift into my hardest gear, set the trainer to hold ERG at 75W, and make the trainer spin as fast as I can. The speed the trainer sends will be high, and would affect distance data calculated by Strava later. I’d recommend reading the following Help Center article we’ve written on the topic:


Thanks Larry,

I started this post after reading that thread and I understand how the gearing affects flywheel and distance. I have been intentionally using harder gearing overall to allow more focus on cadence during workouts.

Let me ask a different question;
What the difference between distances calculated via Strava and the distances recorded by Zwift?

You mention a potential physics model for speed in the future; does Zwift have a model in place that more closely represents distance?

Is there or could there be a way to correlate flywheel speeds and power to representative outdoor speeds? Is that what is meant by ‘physics model)

(This rabbit hole is deep isn’t it?)