Every navigation app you've used has the same instinct: the moment it finds a faster way, it takes it. For a commute, that's great. For a Sunday run over the Cat and Fiddle, it's a disaster. You didn't choose that road to save four minutes — you chose it because it's the best road in the county.
So Tarmac has one rule that sits above every other product decision: nothing changes the route unless the rider confirms it.
What goes wrong with automatic rerouting
On your own, a surprise reroute is annoying. In a group, it breaks the ride. Picture eight bikes leaving a café. Traffic builds on the A-road ahead. Three riders' apps quietly switch them onto a dual carriageway, two stay on the plan, and the rest get a different suggestion because they were a few hundred metres behind. The group is now in three places and nobody decided that.
- The lead thinks everyone is behind them.
- Sweep has no idea who went where.
- The café stop becomes a 20-minute wait while people ring each other.
How Tarmac handles traffic instead
Tarmac still watches traffic. When it finds a meaningful delay, it shows a diversion suggestion with the time it saves and confirmation that it rejoins your planned route. You tap to accept, or you ignore it and carry on.
In a group, each rider confirms their own diversion by default. Some clubs prefer the organiser to decide for everyone, so groups can switch to organiser-only changes.
What about wrong turns?
Miss a junction and most apps invent a brand-new route from wherever you are. Tarmac guides you back onto the route you planned. The plan is the source of truth; your position is just where you are relative to it.
Why this is a product rule, not a setting
We could have made auto-reroute a toggle. We didn't, because a group only works if everyone's app behaves the same way. A rule that holds for every rider is what lets the lead, sweep and everyone in between trust the route.