Distance mismatch between QZ and Garmin

[lengauermario]

Another question — Distance mismatch between QZ and Garmin

Do you know what settings I should adjust so that QZ and my Garmin show roughly the same distance?

Right now, there's a ~5 km difference on a 20 km ride, which feels too far off — especially since I use Garmin to track my rides, compare stats, and take part in challenges with friends.

Current QZ Settings (that I think might be relevant):

• Speed calculates on Power: On
• Rolling resistance factor: 0.005
• Bike weight: 9
• Rolling resistance gain: 0
• Wind resistance gain: 0

Any ideas what I can fine-tune to reduce the discrepancy?

Thanks in advance!

[dosubot[bot]]

Hi @lengauermario! I'm Dosu and I’m helping the qdomyos-zwift team.

The distance mismatch is likely due to differences in how QZ and Garmin calculate and interpret speed and distance data, especially when "Speed calculates on Power" is enabled. QZ uses a physics-based formula that factors in your power, bike/rider weight, rolling resistance, and other settings to estimate speed, which is then integrated over time for distance. Garmin, on the other hand, usually expects speed/distance from a speed sensor profile and may require a matching wheel diameter setting to calculate distance correctly.

To reduce the discrepancy:

1. Make sure the wheel diameter set in your Garmin matches the value used in QZ (often 100mm is recommended for indoor bikes) [source].
2. Fine-tune the speed_gain (and if using ANT+, ant_speed_gain) in QZ. Lowering speed_gain will reduce the reported speed and thus the distance. Start with small adjustments, do a short test ride, and compare the results until the distances align more closely [source].
3. If needed, adjust the speed_offset in QZ for finer calibration [source].
4. Double-check which sensor profile Garmin is using. QZ can only send either power or speed to Garmin, not both. If you prioritize power (which is typical for indoor rides), Garmin may not show speed/distance unless it can derive it from the power profile and a set wheel size [source].

Make one change at a time and test, as even small tweaks can have a big impact. Matching the wheel diameter and carefully tuning speed_gain are usually the most effective steps.

To reply, just mention @dosu.

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[cagnulein]

Garmin calculates the speed based on the cadence, since you enabled the speed based on power setting, qz doesn't. So I suggest to disable the speed based on power setting in qz if you want the same speed Let me know Roberto Viola Software engineer and open source enthusiast http://robertoviola.cloud Il giorno mar 5 ago 2025 alle 06:30 lengauermario ***@***.***> ha scritto:

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Another question — Distance mismatch between QZ and Garmin Do you know what settings I should adjust so that QZ and my Garmin show roughly the same distance? Right now, there's a ~5 km difference on a 20 km ride, which feels too far off — especially since I use Garmin to track my rides, compare stats, and take part in challenges with friends. image.png (view on web) <https://github.com/user-attachments/assets/f7d0f65a-1a8d-42a4-94bc-eea18db48afc> image.png (view on web) <https://github.com/user-attachments/assets/d193dd96-0989-4df2-8d1a-3faf9c6b490f> Current QZ Settings (that I think might be relevant): - *Speed calculates on Power:* On - *Rolling resistance factor:* 0.005 - *Bike weight:* 9 - *Rolling resistance gain:* 0 - *Wind resistance gain:* 0 Any ideas what I can fine-tune to reduce the discrepancy? Thanks in advance! — Reply to this email directly, view it on GitHub <#3597>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAALYWEWFYAGDAQINVJKAOD3MAXNXAVCNFSM6AAAAACDDYIQNSVHI2DSMVQWIX3LMV43ERDJONRXK43TNFXW4OZYGY4DMMJTGU> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[lengauermario]

thanks - I’ll give that a try.