Uber lost $5.24 billion in the second quarter this year and seems to have no clear path to profitability. But even that loss is understated, because a substantial part of the expense is not included in Uber’s income statement and is instead pushed onto drivers: the wear and tear the job puts on their cars.

Most Uber drivers seem unaware of how their job costs them when it comes to the value of their cars. We spoke with more than 50 Uber drivers in Los Angeles, Portland, Austin, Dallas, Houston and Charleston, S.C., in recent...