Honestly, I didn't think much about wear-and-tear and I probably should have. When I calculated it, it was way below a dollar per mile, which makes me curious how you arrived at $4.5 per hour of operation. That sounds like an awful lot.
Are you talking USD? Just curious because you used the dollar sign as a suffix.
It's certainly possible that I'll end up paying down the road for the increase in wear and tear from when I was driving, but at least now I'm in a secure position where I could actually afford the repairs or to get a new car without worrying about paying the bills.
$/hr is sort of an odd way to measure depreciation that is mostly mileage based. In the US, IRS reimbursement for business driving is 58 cents per mile and that's probably not a bad estimate to start with for vehicle costs. (It probably overstates it if you would own a car anyway and you have a vehicle that's more efficient/cheaper to operate than average, but it's a reasonable stake in the ground.)
The mechanics I lived with were boat & big diesel. Those engines (and aircraft) are maintained on an hourly basis. In fact, your car is too: you change your oil every 3000 miles or 3 months. The idea being that there is an expected speed, and you’ve accumulated (say) 100 operating hours after driving 3000 miles, or in any 3 month period. As such, all these guys computed engine/vehicle life in terms of cost-per-hour.
It’s weird to me that just about every piece of mechanical equipment you’ve ever heard of is measured in terms of operating hours, but not cars? Color me skeptical.
As to the 0.58$/mile: an hour at 55mph would be, what? 31.90$?
Certainly there's a correlation between operating time and total mileage. It's going to be different for city driving and highway driving but there's a relationship that holds for most normal use cases.
That said, there are specific costs that are primarily about distance (fuel, tires). Furthermore, probably overly conservative oil change recommendations notwithstanding, essentially all car makers express maintenance intervals in terms of mileage not hours (which could easily be measured). I'm inclined to give them the benefit of the doubt that they know what they're doing.
You're probably aware, but it bears repeating that a lot of that mileage figure goes towards fuel costs, and there have been emergency/out-of-band updates to the figure when fuel costs have increased significantly in the middle of a year.
I don't think the IRS officially breaks it out but the estimates I've seen say that gas is about 20-30% of the total. (30 mpg @$3/gal is 10 cents/mile.)
It's certainly possible that I'll end up paying down the road for the increase in wear and tear from when I was driving, but at least now I'm in a secure position where I could actually afford the repairs or to get a new car without worrying about paying the bills.