When the cases deteriorate and the rubber starts to visibly crack. I don’t ride the road bike that much 😆
When I used to ride TT’s (15 years ago) and ride mostly on the road it was about once every couple of months due to presence of flint on Suffolk side roads combined with 20mm tyres with ultrathin skin walls. Don’t think I ever wore one out.
When i used to commute through London on my road bike, it was monthly otherwise i was getting too many flats. That was for the rear, then they lasted another month on the front…. Used to 7-900 miles per month.
The bad roads and crap on them killed the tyres, it was the cuts that really killed them…
I’ve got a pair of conti’s with over 5000kms in them, they are a bit off the depth of the wear indicators but there is a tiny bit of thread showing in one patch…..I’ve just stuck a tyre boot under this section.
Now i’m worried.
I’ve always replaced tyres when they frequently puncture, up to now the contis have been reliable.