How often should ride-hailing car tires be replaced?

When driving for a ride-hailing service, you can't just look at whether the tires are still drivable; waiting until they reach the wear limit isn't actually cost-effective. My front tires used to wear out quickly on the outside; I initially thought it was a tire quality issue, but after getting a four-wheel alignment, I found the toe-in was off. Now, I regularly check tire pressure, tread depth…