Although bicycle tires have an average duration, this duration is not easily respectable due to many external factors that modify this value. The life of a bicycle tire can vary greatly: from 2000km to 7000km. Difficult to give a number. There are soft models designed for performance (think of the 3C Maxx Terra compounds by Maxxis) up to basic models with hard compounds: in this case the durations are totally different.
That said, there are signs that matter much more than the number of kilometers driven, such as the finished tread, wear, cracks in the rubber, sidewall cuts, poor grip, etc. These factors are only noticeable with a visual impact and there are no tools, or apps, that give us an answer: The dear old good eye.
Tires are essential for driving, that's why it's not a good thing to wear a tire completely to the end of a lack of safety in outings, especially off-road. In addition to a grip issue, we are also talking about lower resistance to punctures. When we see that the side knobs are gradually tearing, it's time to change the tyre, there are no stories.
Another sign that should not be underestimated are the cuts, especially on the sidewall: a cut on the sidewall is a serious sign of weakening which can lead to more punctures and the impossibility of returning these tires to the tubeless version. Ok, there are vermicelli but vermicelli can be torn off and leave you stranded at the most beautiful moment, perhaps ruining a trip with friends.
IN CONCLUSION
Changing tires is of fundamental importance to have fun and not to be left stranded during the ride. Having well-maintained tires is important since the tire is the only point of support that the bike has with the ground (apart from our knees in case of too daring technical gestures). If you want to save something, it's better to go for less technical (and harder) compounds in order to considerably increase their life.
I advise you to also read another interesting articles such as The correct pressure in MTB tires – tire pressure.
