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How accurate is your odometer??

Discussion in 'Gen 3 Prius Fuel Economy' started by kswebb1, Jan 26, 2012.

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  1. xs650

    xs650 Senior Member

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    Also, if you work backwards...

    I have seen data on several new tires where effective circumference based on turns per mile was close to 97% of actual measured tire circumference.

    That would put the neutral axis 3% of the way in from the outer surface of the tread. 3% of 12.5 inches is 0.375 inches or 12/32 inch in US tire speak. Considering 10'32 is a common new tread depth, that is right about at the outer steel belt.
     
    #21 xs650, Jan 27, 2012
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  2. SuperchargedMR2

    SuperchargedMR2 Diehard Rams Fan

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    I haven't tested my Prius yet but I was doing this the past few weeks on my 07 Corolla. The interesting thing about my Corolla is that the speedometer is almost perfect according to my Garmin GPS but over a 100 trip I checked the odometer & the odometer was 4% high. At 100 miles it read 96 miles on the GPS. If the speedometer is perfect, how can the odometer be off by 4%? The tires have about 9k miles on them. Very weird to me. :confused:
     
    #22 SuperchargedMR2, Jan 27, 2012
  3. kswebb1

    kswebb1 Junior Member

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    The. Odometer can be calibrated to show any milage. They want it too.The car makers could make it read two miles in a hundered if they wanted .
    A while ago there were several lawsuits against the car company's because the odometers were reading more then the actual mileage.So if you leased a car etc and ran over you were getting charged extra when you still might have been under the allowable miles.
    Since then I have heard that most car company's have set the odometer to read less actual miles.So that if there is a manufacturing difference they don't get sued again.Which is what I suspect with the late model prius.And would mean that due to this the mfd mpg isn't as far off as as actual as most people think.
    Its not something your gonna see in a few miles you would have to monitor it over many.I notice because I travel the same route I have for 13 years and its almost 80 miles one way.
    Think of it this way in anything less then 3 miles the mfd wouldn't even regiser a 4 percent difference at 3 miles it might just register .1 difference for the 4 percent.And as far as time would be 4 sec a mile if only traveling at 60 mph and less then that of traveling faster.

    So I'm hoping that I can get someone to verify if all the priuses have a similar error on long distance trips.Or not.
     
    #23 kswebb1, Jan 28, 2012
  4. SuperchargedMR2

    SuperchargedMR2 Diehard Rams Fan

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    ^^^ I will post my results when I do get a chance to test my Prius.
     
    #24 SuperchargedMR2, Jan 28, 2012
  5. Teakwood

    Teakwood Member

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    Jeez, Louise.
    How much wood would a wood chuck chuck if a wood chuck could chuck wood?
     
    #25 Teakwood, Jan 29, 2012
  6. SuperchargedMR2

    SuperchargedMR2 Diehard Rams Fan

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    Just for kicks I tested my 95 Previa SC today since I needed to use it. I found that it's very similar to my 07 Corolla. The speedometer reads very close but the odometer is showing 4.5% fewer miles then my GPS logged. Very strange to me as I would think the odometer would be showing a few more miles compared to a few less miles. :eek:
     
    #26 SuperchargedMR2, Jan 29, 2012
  7. qbee42

    qbee42 My other car is a boat

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    Since steel is a lot less elastic than rubber, tires are designed with the steel belts at the neutral axis. They have to be: the belt is not going to stretch, so it forces the issue.

    A tire is essentially a belt connected to sidewalls. Since the belt contains steel it doesn't stretch much. Because of this, the rolling circumference doesn't change much with pressure. It doesn't matter whether the belt is a circle or oval; either way the circumference is the same.

    What small change there is comes from the compression of rubber. The soft rubber covering the tire is compressed by the weight of the car, which slightly reduces the rolling circumference. As the tire becomes more oval shaped, the contact area increases. This decreases the pressure per unit area on the rubber, which reduces the compression, resulting in a slightly longer rolling circumference.

    Tom
     
    #27 qbee42, Jan 30, 2012
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