Odometer accuracy



Recently traded '99 Sienna for '06 Corolla. Now my 13 mile drive to work is a mile or two “shorter”. Problem with odometer…Corolla’s? Sienna’s? Suggestions?



Do a test. Go onto the freeway drive at a steady 60 mph and have your passenger time it to the second over three or four miles. (the little white signs along the freeway are mile markers 123.2 is 123 and 3 tenths miles. Time a couple of runs in minutes.

Are the wheels/tyres original OEM size?

It is not unusual for speedometers to be somewhat inaccurate. They do that intentionally so they and you are less likely to be blamed for speeding.


Or simply set your trip odometer to zero when you pass a mile marker and drive a few miles, then check the trip odometer against the mileposts. If the odometer is off, the speedometer will be off as well.

However, most speedometers read a bit high (65 when you’re really going 63). Yours is reading low (11 miles when it should be 13). If it really is low by 1-2 miles on a 13 mile trip, then you are reading 8-15% low, meaning when you think you are going 65mph you might really be going 76!

The most common reason for this is that the wheels and/or tires are not the factory size. Otherwise, I would want to get the speedometer/odometer unit calibrated or replaced, at that level of error.


If the cops where you live use those roadside radar speed warning LED signs, a comparison of your speedo reading with that flashing sign is a good indicator also. Any odometer error will also display as a speedo error.


Perhaps this odometer is accurate and the one in the previous car was reading more miles than were actually traveled.


a small change in tire size can have a significant effect on odometer readings. if you have a trip odomoter, try to start it exactly as you pass a highway mile marker. If after 10 miles of mile markers, you’re not more than five tenths off, that’s probably within specifications. Be aware that if your odometer says you have driven LESS than the actual distance, your speedometer is also reporting your speed as LESS than it actually is.


First though you have to be sure that the radar is accurate. Those things have accused me of doing 10 over when I was exactly at the speed limit before. And I read a newspaper article once about one in Florida clocking a palm tree at 90.

Best method: Got a GPS? It has a speedometer on it somewhere, most likely. Fire it up. It will be accurate to within about half a mile an hour.


Our departments keep them calibrated.

But you make a good point.


Even “calibrated” radar will be wrong if it is aimed incorrectly. For example, if it is at a 45 degree angle to the travel direction of the car being read, it will only read 1/2 of the true speed of the car.


To be pedantic, I think at a 45 degree angle the reading will be 1/?2, or 70% of true.


To be pedantic, I think at a 45 degree angle the reading will be 1/?2, or 70% of true.

You are correct, I humbly stand corrected.