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I belong to a few off-road bicycle in groups. We ride during the day and at night.

Does anyone know of a smart phone app that would alert the bicycling group leader when one of the group is left behind, meaning when they are more than certain distance far away?

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    If the group is so large you can't easily see when someone is missing, the group is too large Aug 29 '20 at 7:21
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    I suspect cellular coverage could be spotty in off-road areas, and any system would have to be active, polling and transmitting all the time, rather than waiting for a message about one being too far back. So its a design choice between being unreliable, or risk of false positives.
    – Criggie
    Aug 29 '20 at 8:14
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    Also consider this may be ideal for softwarerecs.stackexchange.com because its more about software than a bicycle.
    – Criggie
    Aug 29 '20 at 8:15
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    In 4WD you choose a tail-end charlie. Noone gets passed by the official last vehicle, and everyone in the chain makes sure that they can see the guy behind them. Mayhaps your group needs better protocol ?
    – Pete
    Aug 29 '20 at 11:18
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    @Pete's approach is standard practice in many outdoor activities where multiple participants are spread along a line (river kayaking for example). But things go wrong and you need your eyes on the trail not always over your shoulder, and lines of sight can be poor. A buddy system is also useful, but that can lead to losing the back 2. Some form of technological assistance could be a nice addition to the protocol in some conditions. When hiking I've used 2-way radios in the front and rear subgroups, but a hands-free approach would be better on a bike.
    – Chris H
    Aug 29 '20 at 12:58
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This is an inadequate solution to the OP's problem, which I suspect can't be implemented practically. Garmin and Wahoo are two major brands of bicycle computers, and I suspect that they have the largest and second largest market share for GPS cycling computers (with Wahoo trailing Garmin considerably, and with many other cyclists using non-GPS computers or no computer).

While I'm not familiar with Garmin, they appear to have a feature called GroupTrack, which enables users to opt in to a group ride with tracking. This is almost certainly proprietary to Garmin. It requires all riders to connect on Garmin Connect Connections, and it probably requires all individual participants to opt into live tracking. This would enable the ride leader to see the positions of the other participants during the ride - but, as pointed out by @ChrisH, this is contingent on an adequate GPS signal, which may not be true on all rides.

Wahoo has similar functionality, which I believe is called Find a Friend. I believe this shows all other Wahoo users, provided their (GPS-estimated) distance is greater than 50m from your position (NB: I think that GPS position estimates may have a margin of error of up to about 50 yards/45m). But again, this is limited to Wahoo users.

While this doesn't meet the OP's use case, both companies above enable individual users to share a live tracking link to friends and family. This enables other people to see their friend's position live on a web link. However, this is also contingent on a GPS signal. Additionally, I recall a recent spate of posts that Wahoo's live track functionality was breaking mid-ride, and I believe I've heard that Garmin's live tracking functionality may have been intermittent as well. A more dedicated option here would be the SPOT satellite tracking and messaging service. I believe that long-distance racers may use this; for example, a friend in the North Star Bicycle Race, which goes from St. Paul, Minnesota to the Canadian border and back (over about 4-6 days of cycling), advised people to rent their GPS trackers early (and no, I am not even remotely near her level of long-distance cycling, so I didn't rent one).

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  • Spot also uses GPS, but uploads via satellite. It's more the mobile data signal that's likely to fail - GPS might drop out in a gorge or under heavy wet tree cover but otherwise should be OK
    – Chris H
    Aug 29 '20 at 17:22
  • ... Maybe a stray "not" in the last sentence of the first paragraph. Anyway good ideas (+1), perhaps implemented by the leader having a mobile phone viewing the back marker's live location. All live location apps seem prone to failure, and most rely on Bluetooth between the computer and the user's phone. Battery life would suffer
    – Chris H
    Aug 29 '20 at 17:27
  • Garmin has this GroupTrack feature for sure. It is explained on their website but I've never tried it.
    – Carel
    Aug 29 '20 at 18:08
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I don't believe there's such an app, so here's an app-assisted approach.

It doesn't alert but both clubs I ride with have used WhatsApp location sharing to meet up on the road. Other location-sharing tools exist too. If you use a back marker (a role I've often taken in the slower of my clubs, being fairly strong and well equipped, with maps and a loud voice), their job is to stay with the slowest rider and they could share their location with the leader. With big groups, designating a back marker (or pair of back markers) is worthwhile. They should have the route and good lights if darkness is an issue.

You could run location sharing all the time, or you could rely on starting it if you're dropped - this would be more suited to mechanicals when you're stopping anyway, as I can't really recommend that much fiddling with your phone while riding, even with it clamped to the bars. Setting up a group for the ride (or series of regular rides) would be necessary.

In fact the messaging alone is useful - I've received a few "you ok ChrisH?" messages when I've been dropped from a faster group for reasons including cramp, a last minute reroute, and of course simple slowness. These are best if the leader says where the group is waiting (assuming they are) as you don't want to stop to reply, then come round a bend and see them.

Location sharing relies on a data signal, which is fine for local road rides, or my nearest trail centre, but not much use for wilderness cross-country. Without it there may be push-to-talk radio apps that use a WiFi signal. That should give you enough range. Whether any can display location is another matter.

Update October 2020: If the group (or more likely a leader and back-marker) all use IpBike on their phones as bike computers, IpPeloton (under development) shares the riders' stats across the group - but only if they're in range. This would work for a tight group, but not for a loose one. You'd need to test what's shown when someone drops off, and how far away they have to get. The inherent range limits of this technology mean it's probably not the way to go; either a proper data connection or a WiFi network between riders would be necessary.

Further evidence for the unsuitability of Bluetooth Low Energy is given in this preprint which (in the context of contact tracing) discusses proximity sensing using Bluetooth beacon signals and only being able to the read signal when <10m from the other device.

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    Can't say I would use IpPeloton for this and I am the developer. There is a limit of 8 sensors with ANT and the range is probably 20-30 meters max.
    – Ifor
    Oct 19 '20 at 10:36
  • @Ifor it's good to hear that, from you especially. I never got a real feel for what sort of distance the OP wanted to use, and a group of say 40m long managed form the middle would be rather small. It is however a good example of the limits of this particular wireless technology - to go further you'd need either a data signal or ad-hoc WiFi.
    – Chris H
    Oct 19 '20 at 12:24
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I have personally serious issues with relying on a potentially buggy piece of technology to ensure safety on a group ride. Ensuring everyone in the group is safe is a fundamental human requirement of any group ride, regardless of whether it is a trail ride or on the road.

If you are familiar with ensuring safety in the workplace there is what is termed a hierarchy of controls, where there is a cascade of policies in place to ensure safety within a workplace (figure below).

hierarchy of controls figures

The idea behind this hierarchy is that the control methods at the top of graphic are potentially more effective and protective than those at the bottom. Following this hierarchy normally leads to the implementation of inherently safer systems, where the risk of illness or injury has been substantially reduced.

  • CDC

Here, I would classify the smart phone application as PPE (personal protective equipment), the least safe option, it would only be trusted as a last ditch effort to keep someone safe after all of the other control elements fail.

We could eliminate the issue of lost riders by keeping the group size very small so that everyone is within sightline of one another.

If large groups cannot be avoided, we can substitute the risk by riding on low risk areas that everyone is familiar with if we have to maintain large groups. (Note this is slightly less safe from the first one as someone could still get injured and abandoned.)

We can have engineered controls, by breaking a large group into subgroups with a leader and sweep within each smaller group. (Note this is less safe again, as a whole subgroup could be lost.)

We can having administrative controls by having leaders of the subgroup would then report to the primary ride leader at checkpoints. (If we determine a group is missing, we are already behind the eight ball, hence why it is lower on the list.)

The application would come last in this list. The application would have to be functional (cellular and GPS functioning), the rider would have to be able to use it (i.e, no injury, not panicked, sufficient charge in the battery), and the rider would have to be capable of self-extraction (i.e., reading maps, picking a safe route across the terrain).

This element of risk may be why no one has created such an application as it could be a serious liability risk for any company that does so. To ensure safety you have to ensure that smartphones have cellular access and that GPS signal can be always be maintained, that the riders can use the app and can self-extract successfully. That is a long list of conditions. I don't know where you mountain bike, but in British Columbia Canada few if any rides have cellular and GPS signal making this more of an interesting concept rather than a viable safety alternative.

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  • I'd never thought about it like that - is a great visualisation.
    – Criggie
    Sep 15 '20 at 19:04
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    @Criggie there is field work in remote areas at time as part of my profession, safety plans are a constant requirement.
    – Rider_X
    Sep 15 '20 at 19:07
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Thank you all for the information.

The closest gadget/app that I can find to what I'm looking for is a digital child leash app. The kid wears a special bracelet and if the child is further than a predefined distance from the parent's phone, the bracelet emits a sound alert.

The leader can wear the bracelet and the group riders can use the app. Its not really set up for groups, but it might work for me (one on one), since our group rides off road in the dark and the leader can't keep looking back to see if I'm stuck in the sand. :(

Waiting and sweeping is good, but doesn't always work.

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    Maybe leave the after dark riding for less challenging trails ?
    – Pete
    Sep 13 '20 at 23:04

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