Odometer Accuracy

<div class='quotetop'>QUOTE(pjr @ Feb 19 2007, 05:31 PM) [snapback]392918[/snapback]</div>

Find a highway with mile markers. Reset the trip odometer when you pass one. Drive 20 miles or so and see how far off you are.

 

<div class='quotetop'>QUOTE(Marlin @ Feb 19 2007, 03:36 PM) [snapback]392922[/snapback]</div>

Or get a good quality large-scale map of your area and measure a distance of at least ten miles (preferably a very straight road) which you travel regularly

 

<div class='quotetop'>QUOTE(pjr @ Feb 19 2007, 12:31 PM) [snapback]392918[/snapback]</div>

Yeah, I heard the news today on TV and saw this story http://www.detnews.com/apps/pbcs.dll/artic.../702200320/1148. I'm going to post a separate thread on that later.

Another way to check would be to use a handheld GPS unit w/built in odometer functionality.

As a side note, Car and Driver magazine had an article on the issue of odometer and speedometer accuracy at http://www.caranddriver.com/features/1906/...er-scandal.html. The results XML link is dead but this link works: http://www.caranddriver.com/features/1907/...er-scandal.html.

I have not noticed any significant odometer difference, but you've got me wondering. I should compare my Z and my Prius to see how far off their odometers are from each other over identical routes to work (~24 miles 1 way).

 

<div class='quotetop'>QUOTE(pjr @ Feb 19 2007, 03:31 PM) [snapback]392918[/snapback]</div>

I have a 2005 Prius. In three of my previous cars(all different makes) I averaged 8000 mi/yr. My Prius 10000 mi check came just under one year...curious, but I thought..okay maybe I am driving more..? Now my 20000 is coming up well short of two years (x 3 mo.) I check it myself (finally) via a mile marker on the highway...it came up 1.2 mi. I checked at 1.5 mi it came up 1.8.. I have asked this to be check at my next visit...(tomorrow).

 

This is really the wrong forum for this question. This is the Website Questions forum. However:

Both my 2004 Prius and my previous car (1989 Honda Civic) were a bit off. I forget the exact amount. A couple of percent, I think. Both cars' odometers said the car had gone farther than it actually had. Now that I have a GPS in the car, I can also say that the speedometer says the car is going a bit faster than it is. At surface-road speeds I'm going about 1 mph slower than the speedo says, and on the freeway I'm going about 2 mph slower.

This of course will also mean that my mpg is not quite as good as the car claims, since the car thinks it has gone farther on a given amount of gas.

I keep my tire pressure at 42/40, so if the tire inflation were causing the error, it should be in the other direction, unless my HydroEdge tires are actually smaller than the OEM tires.

 

To follow up on my earlier post, I found my Prius' odometer to read a lower # of miles than my Z's. When driving from home to an identical point at work via identical routes, the Prius odometer read 24.2 miles vs. 24.4 on my 350Z.

Hopefully one of the mods moves this thread over to the proper section.

 

<div class='quotetop'>QUOTE(cwerdna @ Mar 10 2007, 06:33 PM) [snapback]403561[/snapback]</div>

Eight-tenths of a percent is so close I'd consider them identical for all practical purposes. But you could still go out on a highway and use the mile markers to calibrate for sure, since comparing two cars does not tell you if either of them is accurate. If you can borrow a GPS that would be easier.

 

<div class='quotetop'>QUOTE(daniel @ Mar 11 2007, 09:55 AM) [snapback]403742[/snapback]</div>

Around 2% is the variation between new tires and worn tires. Mile markers (unless labeled as measured miles) are not very accurate. The GPS is a better idea. I have only seen the measured miles in a few states and then in only one or two places. If you are going to use these mileposts, try to do a 5 or 10 mile run to average out the variations.

- Tom

 

i started a thread and wondered about the accuracy too. i keep my tires at 42/40 and noticed the speedometer was off by 2 miles when using my gps unit. so i checked it against the 5 mile marker on the freeway and the odometer seems off by a tenth, just an estimate. so it seemed every 5 miles would mean the prius thought it drove a tenth more than it did, which means it would take 50 miles of driving for it to be off by a mile. seems many other prius members here have the speedometer off by 2 miles also. when i hit my second set of new tires at the end of the year, i'm going to get a taller tires(taller tires should give less revolutions per minute) to help me lower the inaccuracy.

 

<div class='quotetop'>QUOTE(daniel @ Mar 11 2007, 07:55 AM) [snapback]403742[/snapback]</div>

No need. I have a handheld (very old) Magellan Map 330 GPS unit. On the same route as I mentioned before, it was today:
24.4 mi on 350Z [same as before]
24.14 mi on GPS unit

I will have to do another run w/the GPS unit when I have more time to let the GPS unit average after initial lock. There a large amount of error and "drift" on these Magellans after the initial satellite lock.

 

My experience for all my cars is that the speedometer is generally biased to read high 1 or 2 mph at freeway speeds. I don't think I have ever seen a car read low.

Having said that, I was going to let this fact influence my tire selection the next time I buy new tires. For example, the Michelin Energy Plus tires are just a little larger than the original tires... and that would tend to make the speedometer/odometer reading just slightly lower than currently.

 

<div class='quotetop'>QUOTE(cwerdna @ Mar 14 2007, 04:17 AM) [snapback]405254[/snapback]</div>

With a small amount of handwaving given the resolution of the numbers, this is only a 1.07% variation. Since the car is only reading out to tenth's, it could be a bit better or worse, but it is well within the 2% you will see over the life of the tires. If the tires are new, it will get worse (rise to 3% fast) as the tires reach the wear bars. If the tires are close to worn out on your car, then new tires of the same brand and size could switch the variation to be 1% in the other direction.

I don't see anything outside of normal expected accuracy. Good job on doing this over a reasonably long distance instead of only a couple of miles!

- Tom

 

<div class='quotetop'>QUOTE(John in LB @ Mar 14 2007, 05:21 AM) [snapback]405267[/snapback]</div>

I have a hand-held Magellan. I bought it for hiking, and intended to use it also to precisely find the mile points on my jogging routes. It was so far off for distance it was ridiculous. Something like 1/4 mile off in a 3-mile route. However, if I recorded the Lat and Long, then plotted those on the computer in the included software, I got the correct distance, as near as I could tell.

I have not used the hand-held for a long time. It is a nuisance to carry, and in valleys it can lose the satellites. In my car I use a Garmin StreetPilot 2720 and I like it a lot.

 

<div class='quotetop'>QUOTE(daniel @ Mar 10 2007, 05:36 PM) [snapback]403545[/snapback]</div>

I'll second that. Moderators, please move this thread to the appropriate forum.

Thank you.

 

This is a long delayed response to this thread - I have found my 2005 Prius to consistently over read speed by 3% at 100k, when checked against a GPS. ( ie the speedo says 103 when travelling at 100kph)
Presumably this corresponds with a 3% over recording of distance covered as well

Chris

 

OT - Dunedin is one of the nicest cities I have ever been to. It was one of the highlights of our trip to NZ in 2004. If I lived there, I wouldn't be at all concerned about the accuracy of my odometer. I would just enjoy life.

:focus:

 

My odometer is very off. We checked it with the mile markers in 3 different states & for every 40 miles we traveled, the car counted 43+. I also know for a fact that I haven't driven more than 25,000 per year... my car says I've driven over 31,000 per year. Now that I need to trade it in for a bigger car no one's willing to give me near what we need for it because of the high miles.