It all depends on the year and how long I am willing to keep riding on slowly deteriorating tires. I have had either 5 or 6 so far this year if I recall correctly and they have all been on my commuter that wears Panaracer Gravelkings 32mm. The rear tire is quite worn and it caught up to me tonight. I was heading into work at 930PM when I suddenly felt that now too common bouncy feeling emanating from the rear wheel. Another in and out flat. I quickly patched the tube and was on my way again in 15 minutes but this flat fix at night has convinced me it is time to replace the rear tire at least. I did make it to work on time though.