Anonymous
Anonymous asked in Cars & TransportationOther - Cars & Transportation · 10 months ago

# Google maps vs odometer accuracy?

Which is more accurate in terms of distance - Google maps or my car's odometer?

There is a 2 km discrepancy between them - my car measured 402 km and goodle maps showed 400 km. I know 2 km might not sound much but I am wondering which one is the accurate. I am certain however, that my tires are properly inflated, that they are the right size too.

What is your experience regarding the issue?

Relevance
• 10 months ago

Odometer. Google measures the distance by approximating how far you are away from your destination. It takes point a to point b, measure in a straight line how far they’re apart. Then if approximates the curves and turns, and it arrives at a number. Your car actually measures every meter that your wheel travels.

The best way to describe google maps is like using calculus to find the length of a weird squiggly line. It breaks it down into tinier straight lines then adds them together to get a length but the accuracy depends on how many pieces you break the lines into. I doubt google breaks it down into 1 meter segments.

• D50
Lv 6
10 months ago

Tire size is always changing - they are getting smaller as they wear. I think GPS adds up your distance travelled incrementally, like an odometer, but is also subject to little variations, since it only knows your position approximately. I would guess that the diff you see between the odometer and Google maps is typical but there is no good way to judge which is more accurate over any particular route.

• 10 months ago

That's 0.5% difference.  That could easily be produced by under/over inflating tyres, or simply by tyre wear. The odometer simply counts the number of times the wheel turns. Google makes the best estimate, probably by measuring along the centre line of the roads, and that's not the actual line you drive. I doubt a GPS tracker would give a "better" result, though it would probably give a different distance.

• 10 months ago

Check your speedometer against a GPS unit. That will show you how accurate your speedometer is. It could be right on the button if you have the right size tires. The odometer does not show distance traveled in reverse, but who drives 2 kilometers backwards?