Hi everyone,
I contacted Suunto Support regarding an issue with Heart Rate zone distribution and TSS calculations for activities synced from my Hammerhead Karoo unit.
Currently, third-party imported activities ignore custom HR zones set on the watch and instead rely on Suunto’s default backend algorithms. As a result, rides synced from my Karoo end up with mismatched HR zones (e.g., shifting Zone 2 efforts into Zone 1), which directly distorts HR-TSS, CTL, and ATL tracking in the Suunto App.
I strongly request that Suunto allows manual HR zone configuration directly within the Suunto App (or enables synced activities to respect the watch’s custom HR zone settings/LTHR). This would ensure that data imported from head units like Hammerhead is categorized accurately.
Below is the official response I received from Suunto Support confirming this current limitation:
Thank you for contacting Suunto Support and for providing the detailed information.
We understand that you are recording cycling activities with your Hammerhead Karoo 3, which are then automatically synced to the Suunto App, and that you have noticed differences in the heart rate zone distribution between the Hammerhead platform and the Suunto App.
Regarding imported activities from third-party platforms, the heart rate zone analysis displayed in the Suunto App is calculated based on the settings and algorithms used by Suunto. The HR zones configured on your Suunto Race S watch may not be applied to activities imported from other services, which can result in differences between the original platform and the Suunto App.
At the moment, the Suunto App does not support setting independent heart rate zones specifically for imported third-party activities. Therefore, there is currently no setting available to force imported activities to use the HR zone configuration from Hammerhead.
We appreciate your feedback regarding this functionality. We will forward your comments to the relevant team as user feedback for future improvements.
Thank you again for your understanding and support.
Kind regards,
Suunto Support Team