Speedo Correction ?

Discussion in 'General IH Tech' started by Albuq. Henry, Jun 15, 2011.


  1. Albuq. Henry

    Albuq. Henry Binder Driver

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    Ok I just went with my wife to the next town 30 miles or so to get a set of used tires she found on craigslist. I figured it would be a good time to see how far off my speedo is and see what gas mpg i am getting on the highway.

    First was seeing how far off my speedo is..

    I traveled from marker 193 to 203, 10miles

    My odometer said 257.7 at start and 265.3 at 10 miles. 7.6 miles

    so 7.6 times 32% equals 2.4.

    7.6 plus 2.4 equals 10

    so my speedo is off by 32%??





    So I put 2 gal of gas in my empty tank. according to my odometer....I switched tanks to the two gal. at 266 and I ran out at 278. 12 miles.

    12 miles times 32% equals 3.84

    so I really travled 12 plus 3.84 miles .... 15.84 miles

    devide that by the two gallons. 7.92 miles per gal.


    I was on the highway speedo says 60mph... muliply by 32% equals 19.2
    60 plus 19.2 equals 79 mph. I was really going 79 mph??

    Did I do all of this right??

    My brain hurts....:no:
     
  2. Erik Morton

    Erik Morton High Wheeler

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    Your math seems OK. And if you are going 79 that would explain the low mileage. That and the 10 mile range is too short to measure mileage accurately. Your truck may not even be fully warmed up.

    Now assuming your 32% correction factor is correct carefully log several tankfuls not just 2 gallons. That will give you a much better idea. How did you measure the two gallons? An empty gas pump hose can suck up a lot of that 2 gallons.

    There are a couple of other ways to verify your speedo/odometer accuracy. A GPS will give you another means to verify your 32%. Just watch and compare with your speed. Also you can compare your odometer changes with know road distances. There is a website for bicyclers that measures the distances of road routes. Spend a day driving and recording Odometer readings. In the evening find that site and see how far you really went.
     
  3. Albuq. Henry

    Albuq. Henry Binder Driver

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    I was hoping I am on the right track...

    For the two gallons, the other day I ran out of gas on my pass side tank. I pulled off the highway today and bought two gallons at the pump and put it in that tank.. when back on the highway I switched to my pass tank and went the distance I stated earlier and had to switch back....
     
  4. Crikey Mate

    Crikey Mate Farmall Cub

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    I get similar numbers with the way I usually work it out but you may find this way easier in the future -

    The conversion factor you're after is Actual/Measured.
    In your case that's 10/7.6 = 1.32
    You can recalculate that if you do what Erik suggests and take some more readings. Then you just need to multiply any speeds/odometer readings by 1.32 (or whatever you get).

    60mph x 1.32 = 78.95mph
    12m x 1.32 = 15.79m

    Don't ask me any more maths questions, I only know this one because I haven't managed to fix my fuel gauge yet.

    EDIT: I haven't had a coffee yet and I just realised my 1.32 is the same as your 32% but this may be another way of working it out!
     
    Last edited: Jun 15, 2011
  5. Albuq. Henry

    Albuq. Henry Binder Driver

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    ok glad it came out simular a different way... the first time I did it i though I was 25% off.

    7.6 is almost 7.5
    10 minus 25% equals 7.5
    But that was going from correct to the incorrect...
     
  6. Doc Stewart

    Doc Stewart Content Team Staff Member Moderator

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    The error can be corrected by using a gear corrector between your speedo cable and the Transfer case connection.
     
  7. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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  8. Albuq. Henry

    Albuq. Henry Binder Driver

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    Bill, Thanks for that link. Ill have to see what I have in there then see what they can do for my dana 20..
     
  9. Bill USN-1

    Bill USN-1 Moderator Staff Member Moderator

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    GM / Dodge / Ford Ratio Adapter



    #54RA. This GM / Dodge / Ford ratio adapter will slow your speedometer reading down. Made for low rear end ratios with short tires. Offset for clearance reasons. If your GM speedometer reads too fast with 15 and 45 teeth gears then you need this part. This part will slow down your speedometer reading. Use this one to convert Kilometers to MPH. Cost $62.00
    Qty 123
    Slow Down Rate Select the Correct %Slow Down 50%Slow Down 37.5% Converts Kilometers to MPHSlow Down 26.7%,Slow Down 17.6%Slow Down 10%Slow Down 2.56%


    #54RA2. If your truck tires have been switched to larger tires or you just need to speed up your speedometer this one will correct your problem. This part will speed up your speedometer reading. Use this one to convert MPH to Kilometers. Cost $62.00
    Qty 123
    Speed Up Rate Select the Correct %Speed Up 11%Speed Up 20%Speed Up 28%Speed Up 38%Speed Up 44%Speed Up 61% Converts MPH to KilometersSpeed Up 78%Speed Up 100%


    Other ratios available on special order, allow 2 to 4 weeks. No refunds on special orders. The male side can be turned 180 degrees, just remove the 4 screws and turn. We can slow your speedometer down as much as 58% or speed it up as much as 200%. Cost $72.00




    [​IMG]
     
  10. DavidWTravelallfan

    DavidWTravelallfan High Wheeler

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    Also consider the fact that your probably not getting a real 2 gallons of gas at the pump. Take a gas can that you know how much it holds. Fill that up at gas station, then pour into the truck tank.

    You make me feel better..I thought my Travelall was bad around town at 8 mpg:yes:
     
  11. Albuq. Henry

    Albuq. Henry Binder Driver

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    now that I know how to figure the correction Ill start tracking my mph... I am pretty sure that is the worst milage Ive gotten so far.... That was also the fastest I have ever drove the scout...
    To and from work I was thinking the scout did about the same as my 94 cheby k1500 based on how much I spend...
     

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