In preparation of selling or trading in my 95 Honda Accord, I was doing a little blue book valuation of it. When I got to the part about mileage, it made me stop and think. Is this really the best way to track a cars use? Everyone knows that city miles are harder on a car than highway miles, but there is no way to objectively look at a car and say, "That car is a good deal because it's engine was treated easier than this other one."

The way I see it, mileage only has a direct correlation to things like tires and suspension (maybe).

Wouldn't it be better to add RPM tracking? (You could use average mph tracking but that would be nulled by all you low gear high rev guys out there!) Let me give you an example.

Take two cars. Car 1 was mainly city driving. Let's estimate the average speed of the cars life was 30mph (stop and go traffic, etc.) Car 2 was maily used for highway commuter stuff. Let's estimate the average speed was 50mph. Now let's assume for simplicity sake that the average RPM for both cars at those speeds is about 3000rpm (doesn't really matter). Both cars have 100,000 miles.

Car 1: 100,000 miles / 30mph = 3333 hours
3333 hours * 60minutes/hour = 200,000 minutes
200,000 minutes * 3000RPM = 600million rotations
Rotations per mile average = 6000 rotations per mile

Car 2: 100,000 miles / 50mph = 2000 hours
2000 hours * 60minutes/hour=120,000 minutes
120,000 minutes * 3000RPM = 360 million rotations
Rotations per mile average = 3600 rotations per mile

You can see that the engine in car #2 has seen a lot more work, motion, whatever. You could also infer from this ratio truly how much of a "highway" car it was or wasn't.

This could also have maintenance implications. Take my timing belt. The manual says change every 90,000 miles. If the belt has cycled half as many times as in a city engine, do I have to do it as often.

I know that many manuals have different sections for city/hard driving and highway/easy driving, but wouldn't this take the guesswork out of it?

What do you think?

let's not also forget about idling, as that's pretty hard on an engine too (it kills me when i see all these idiots in their pseudo big-rigs pull up outside the garage where i work, to leave it idle for 15 mins when they come to pick up their boats...)

that's why boat engines work on hours of operation, rather than distance travelled...
hmmm... but yeah, if we tracked the amount of work the engine's done (ie, amount of revs and at what kind of throttle angle, stuff like that... something really really stupidly complicated) we'd get an awesome picture of how hard the car's been working...

i too thought about it, and now that almost everything on a car is quantified, cut and dry by the engine comps, it should be done. then we can really see if that guy who says his engine "only" has 40k on it is definitely better than the other guy's with 95k on it... :) cool freakin' beans.