Odometer Measurement Miscalculation?
 

so i went to my dealership today for my 10K scheduled maintenance and i wanted to ask them about a problem that i have noticed with my car. the last long distance trip i made to dallas a few weeks ago to get my car fixed by Newtlicious, i noticed that the odometer mile count wasnt corresponding with the actual distance of the mile markers on the road. i calculated it out and i believe that my car was off ~5 mi per 100 miles. so while i was at the dealership today, i ask the technician if he knew anything about this and he told me that some ppl with miatas had the same problem. however he couldnt recall the actual explanation bc it occured a year ago. he said mazda intentionally overcalculates the mileage in their cars...i have to go back to the dealership next week and the technician said he'd have an explanation for me. any idea's guys? or is this just the dealership blowing wind again... :confused:

have you made any changes in your tire size?

my car is 100% stock

there's always a 2 or 3% difference between the odo read and the actual speed you're travelling, but 5% seems a bit high IMO. I have put 235-40-18 on my 8 and now i'm 4% high on my speedo. (reads 100 and my gps tells me 94) the same at 120 (GPS says 115)

oh, it's KPH not MPH :-)

I drove by a unmanned radar unit the police setup to show you your speed. I knew it existed, so I set the cruse control to 35 mph. This radar showed me to be traveling at 32 mph. This is a 9% difference. Because this radar isn't in use for actual law enforcment, I don't know how accurate it is.
I guess I will just drive faster to hit a designated speed.

With my GPS i have to do 52 (speedo) for 50 (GPS) and obviously 104 (speedo) for an actual 100 (gps)

all measurements MPH.

The Speedometer claibration and odometer calibration are performed separately. The original post asks about the odometer. Odometers are typically more accurate. Spedometers almost always read high due to European regulations (high penalties for under reporting the speed).

OK "Thread Police"

I guess i could check by using my GPS with the odo..how far do you think would be a good distance to accurately check. we have some pretty straight roads in montana that would lower the chance of the GPS cutting corners as they can do at speed.

oh or better yet next week i am going down 395 in WA that road is stupid straight. the most boring road i have ever been on. (anybody know what i am talking about?)

Mile markers are the easiest to check the odometer like Takahashi did (use 10 of them to make calculation easy and average the errors)

GPS is very accurate for checking the speedometer (assuming you have a good lock on at least 4 satellites)

well my car is at the dealership right now and being evaluated. I will let u guys know the status later on...

I think this sucks
 

I noticed that my car is off too and I may have it addressed too. I am leasing the car and I should not be paying for miles that I don't actually use. The same can be said for the warranty. I determined that every ten miles I went the odometer claims I went 10.3. I guess I would hope it would be more accurate than that.

Maybe I'm just too mistrusting, but I wonder why no one has questioned the accuracy of the road markers instead of the odometer.

mile markers are usually surveyed in. They are also used for costing by the government and contractors. Both parties want them to be fairly accurate.

Hmmm, maybe Mazda is trying to increase the RX-8's perceived mileage anyway it can...

takahashi j - please let us know what you find out. I've already racked up 3300 miles in a little over a month and it just doesnt seem right.

We already know the speedos are off 2mph, but if the odometer is off 3/10 of a mile as well then something better be done or it will be a whole new can of worms for Mazda.

Hate to think that for every 3000 miles on my odometer theres an "additional" 900 or so miles that I haven't driven....

On the other hand we all might be getting better mileage than we think! lol

30% off is not realistic IMO, 3% is possible, but 30% ? no way :-)

My brain calc misfired...still, an odometer should be dead on especially when warranty issues and more importantly resale values are derived from the odometer. Hell, you have to sign a statement regarding your odometer when you sell/trade a car.

I want to hear what takahashi j is told.

indeed, it should be accurate for legal purposes.

well guys, sorry for the long hiatus (i was in canada for the past week). when i finally got my car back, they said that they manually tested accuracy of the odometer by reseting the tripmeter every few miles and used the same technique i did (on the freeway). the techs could not "replicate" the problem. they also said they checked the "computer" and everything was to spec. I dont know where to go with this. I also havent had the chance to retest it's accuracy since ive been back. i will try to get around to it soon. bs?

is this still a problem with newer RX8's, because I too have put a lot of miles on mine. it doesn't seem right.

Bought it in sept new with about 12 miles now I have over 10,000 miles.

thanks
rip

I wouldn't worry about it.

Wouldn't you be getting worse mileage? You've only driven 100 miles but the odometer says 130 miles. It's overstating the amount you've driven and hence overstating your mpg :-P

yes^^. in general speddo's and odos an be as much as 5% off although some companies have reported nearly 10% to be within "operating tolerances" they always over report as mentioned above- as always ymmv ;)

My speedometer is high by about 5%. That's based on driving past "Your speed is..." stationary radars and by comparison with GPS. Haven't clocked it against measured miles.

Next road trip I'll try to check the odometer against mileposts. If the odo is off by the same as the speedo, they're cheating me out of 5% of my warranty.

FWIW, the speedometer on my wife's Camry is right on, compared with GPS.

Ken

last december i clocked the car against a hand held gps. 75 mph on the speedo, 72mph on the gps unit.

it was ~1mph per 25mph off. roughly.