How It Works
This automatic feature detects if you recorded your activity at the same time as other users on the same route. When a group activity is detected, your activity becomes linked to any matching activities. To detect a group activity, our algorithm considers the percentage of the elapsed time in your activity during which the other activity is "nearby."
If the other activity is nearby for more than 50% of the time, it is considered a match. This threshold allows for other users to join a group ride or run partway through, or leave early, as long as they match the set percentage.
The algorithm is asymmetric. For example, if you join someone for the last 5 miles of their 50-mile ride, it will say that you rode with them, but not that they rode with you. In most cases, however, matching is symmetric.
The algorithm is activity type agnostic (for example, skiing can be matched with snowboarding).
"Nearby" means closer than a few hundred meters together. However, this rule is more flexible for longer-distance activities.
On your feed, the group activity is displayed with one map and a list of the group members you follow below.
Please be aware that if you've hidden any portions of your map, and an athlete you're grouped with records within that portion but doesn't hide it themselves, the map in the feed will display that athlete's polyline within that portion.
When viewing an activity details page, you will be able to view the full list of athletes matched in the group.
Long Story Short
We'll automatically group athletes with activities scheduled at the same time and routes that are more than 50% similar.
Leaving a Group
You can remove your activity from a group from your account on either the Strava website or mobile app. From your activity page, click the icon of the grouped athletes to find the Leave Group option. Be aware that if you are viewing the activity of another athlete in your group, you won't see the option to remove yourself from the Group Activity. Learn more about additional Group Activity Privacy Controls.
Troubleshooting
Sometimes our servers take a bit of time to complete the grouping process, especially for larger groups. If you are still not seeing your activity grouped after about 12 hours, please check the following:
If you've set your group activity privacy controls to "No One," no athletes will be grouped to your activity, nor will they see you as part of a group.
If you are a Strava mobile app user, check your device's internal clock settings. If you set your phone's clock manually, your time could be off by over 1 minute from the automatic clock based on cell towers/satellites, causing you to miss the group activity detection. Instead, try setting your clock to update automatically.
If you're still having trouble, submit a support ticket that includes direct links to your activity and the activities you should be grouped with.
Please be aware that the option to Add Others/Friends does not allow you to retry the automatic grouping, nor does it allow you to manually group your activity with other activities that are already on Strava. The Add Others/Friends option allows you to invite a friend who was with you but didn't record their activity on Strava. If the invitation is accepted, your activity will appear on your friend's Strava profile and feed as if it were their own. Learn more about inviting friends to your activity here.