Going the distance

[Enzo]

SO traditionally, the odometer on the car was a mechanical thing, and if one were so inclined, one could jack up the rear end, put the car into reverse and let it run and it would subtract miles from the odometer reading.

Nowdays they are digital. I wonder if the same thing can happen, reverse driving subtracts miles, or does it recognize that travel in either direction is still travel, and it counts reverse miles same as forward?

Inquiring mind wants to know.

[Heid the Ba]

SO traditionally, the odometer on the car was a mechanical thing, and if one were so inclined, one could jack up the rear end, put the car into reverse and let it run and it would subtract miles from the odometer reading.

On some models it was possible to disconnect the odometer and take a power drill to it to reduce the mileage.

Nowdays they are digital. I wonder if the same thing can happen, reverse driving subtracts miles, or does it recognize that travel in either direction is still travel, and it counts reverse miles same as forward?
Inquiring mind wants to know.

I have no idea, and it is unlikely I'll ever drive far enough in reverse to find out.

[Lianachan]

I had no idea that distance driven in reverse was subtracted from mileage. I've certainly heard of the practice of putting the mileage back, but I thought there'd have been more to it than that.

[Enzo]

Yes, the power drill method is much more efficient, but it does leave tell-tale evidence of tampering in the dust under the dash. The jack up the car idea is really more of an idea than anything practical. Think Ferris Bueller movie.

And the odometer incremental counter itself is the same as the thing in an old cassette deck or something. Someone familiar with them can take it out, and by holding the pawl back, can spin the wheels freely to whatever setting they want. it can be difficult to get the numbers properly aligned, and this method also leaves clear evidence of tampering. Of course the consumer will never take his dashboard apart, but if someone were to investigate...

I suppose I'll just have to drive in reverse a couple tenths of a mile if I want to know.

[Мастер]

I had no idea that distance driven in reverse was subtracted from mileage. I've certainly heard of the practice of putting the mileage back, but I thought there'd have been more to it than that.

I think this appeared in Ferris Bueller's Day Off (or have I mixed up my films), although I assumed the people doing it were confused. I didn't realise this was a technique that actually worked.

it can be difficult to get the numbers properly aligned, and this method also leaves clear evidence of tampering.

If you drove it a short distance after doing this, would the alignment straighten out, or would it be permanently misaligned?

I once knew someone (this was in the US) who bought a used Honda Prelude, then discovered the service log that came with the vehicle had a record of a maintenance at a higher mileage than was showing on the odometer.

[Lance]

I don't think this has worked for a very long time, even on mechanical odometers. They fixed it a long time ago to prevent this kind of fraud.

The numbers would never realign. They move "one space" each time so if you put them together out of alignment that will remain so. I speak from first hand experience.

[Мастер]

I speak from first hand experience.

True confessions?

[Lance]

I speak from first hand experience.

True confessions?

It was a junk car of a friend when I was a teenager. We were just wondering how it worked. But even then, driving in reverse didn't run the numbers backwards.

[MM_Dandy]

It didn't work in the movie, either. And the car was supposed to be some sort of classic, like a 60's Jaguar or something.

[Enzo]

The numbers would eventualy realign but each wheel will only snap into sync when it moves. SO if the 10,000's digit is off a hair, you have to drive 10.000 miles for it to increment.

In the movie, it failed largely because he knocked it off the bumper jack and launched it out the rear window.

[MM_Dandy]

Ultimately, yes, but it was realized that the odometer wasn't rolling backwards before that.

[Enzo]

Ah. I have to admit when I watched the movie I didn't watch that close.

Having done a mite of research a moment ago, apparently since the advent of digital car systems, the odometer is now smart and increments regardless of direction. I have no proof yet, but as soon as I back down the highway, I will report.

[Enzo]

I did in fact drive in reverse last night far enough to see that the digital odometer does indeed increment forwards as I drive in reverse.

[tubeswell]

But a negative integer added to a positive integer cannot be a more positive integer! There should be a name for that type of odometer.

[MM_Dandy]

Seeing as one cannot travel a negative distance, it would be the pedantically correct odometer?

[Enzo]

Hmmm, my life has been a series of negative advancements.