Race Engineer weighs the pace you'd gain from fresh tires against the extra time a stop for them costs, using this car and track's own recorded history.
Expected time gained from fresher tires, minus the extra time the stop takes. That math runs separately for every real option (all four tires, just the fronts, just the rears, or a single corner), and the app recommends one only if it pays for itself over the laps you have left.
When this car and track do not have enough recorded stints and stops, Race Engineer shows "NO VERDICT" with low confidence and says what is missing, for example how many more stops with and without a tire change it needs.
Pace loss and pit-time cost both come from your own past sessions with this car and track. Race Engineer also shows how close it is to having enough samples.
Once a tire change is worth it, the recommendation stays on screen (above iRacing, without stealing focus) for as long as it's still true, the same always-on-top treatment the fuel overlay uses. It disappears on its own once the recommendation changes, or you can dismiss or pin it yourself.
This tire recommendation is independent of the pit window described on the Pit Strategy page, which is built from fuel only today. Each is its own signal: one can appear without the other.
It tracks wear per corner and shows it on the Tires page. The change recommendation comes from the pace your stints lost in your recorded sessions with this car and track. A formula that turns wear into lap time has not been validated on real data yet.
Because the pit-time cost of changing outweighs the time you'd gain from fresher tires over your remaining laps. Staying out is the actual best option in that case.
Race Engineer has no history to learn from yet, so it shows NO VERDICT and recommends no change. The Tires page lists what it still needs, such as how many stops with and without a tire change.
Yes. It evaluates all four tires, both fronts, both rears, and each individual corner separately, and recommends whichever one actually pays for itself.