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  1. #1
    Veteran Member Three Rings SKIDMRK's Avatar
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    Speedometer Accuracy

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    Had a bit of an experiment tonite.....

    I had set my cruise control at 70mph, but was fiddling with the Alpine nav and noticed that it said I was only going 67mph.

    Out of curiosity, I switched the MFA to the average speed, reset it so it would start fresh, and noticed that it only read 66mph.

    What I find odd is that the speedo reading and the MFA reading are so much off.

    Has anyone else noticed this much of a variance or am I just being anal thinking that Audi could have at least synched the speedo and MFA.....
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  2. #2
    Veteran Member Four Rings Re5pectThe_Cuz's Avatar
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    Re: Speedometer Accuracy

    do you have aftermarket wheels on your car?
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  3. #3
    Veteran Member Three Rings SKIDMRK's Avatar
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    Re: Speedometer Accuracy

    I do, but the variances on the factory MFA and speedometer which has nothing to do with tire diameter is what puzzles me. Just wondering if anyone else has the same variance.
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  4. #4
    Senior Member Three Rings Race Shooter's Avatar
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    Dec 22 2006
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    Re: Speedometer Accuracy

    If its like VW (which it likely is being VAG), they actually set the speedos to read a bit fast in order to have some wiggle room and make sure that with any tire size variation (due to inflation or spares or the slight differences in stock sizes) and anything else that might affect speed, does not EVER make the speedo read slow, since its a violation to have a speedo read slow. Its pretty common to have them off by about 4% and is about the same in every single VAG car I have owned since about '85.

    The reason your MFA is correct is that due to laws and all that jazz, they have to insure that the odometer is absolutely accurate and therefore it runs off a different circuit or source than the speedo does. The MFA is tied into THAT source to make all its calcs that have to do with distance, so in the end the MFA is the more accurate of the two.

    Its also why it matches your GPS much closer as well.

    How they can make one accurate and have to have "room" in the other is beyond me, but thats how it is.
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  5. #5
    Veteran Member Four Rings dummptyhummpty's Avatar
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    Los Angeles, California

    Re: Speedometer Accuracy

    I remember reading that the speedometer was off by 5mph (it shows 40 but you are going 35). I hate knowing that.
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  6. #6
    Veteran Member Four Rings gdawg'05a4's Avatar
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    Re: Speedometer Accuracy

    Mine is 3mph off, speedo says 40 but going 37.
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  7. #7
    Veteran Member Four Rings Papachristou's Avatar
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    Sep 15 2006
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    04 Audi A4 USP,05 S4 Cabriolet
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    Re: Speedometer Accuracy

    all my cars have done the same going past those radar signs and stuff too but who knows how accurate they are ?
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  8. #8
    Veteran Member Four Rings Ultrasport Steve's Avatar
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    Re: Speedometer Accuracy

    It is about 3-4 mph off at 80 mph...shows 80...actually doing 76-77.
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  9. #9
    Veteran Member Four Rings DenverNoob's Avatar
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    Re: Speedometer Accuracy

    the diff between my speedo and my gps is steady at 3mph through about 75mph...the 4mph after that....so when i read 120, im only doing 116....BOO!

    i love knowing that, because when im doing 5mph over on my speedo...im not really ticket worthy to the cop im passing! (knocks on wood).
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  10. #10
    Veteran Member Four Rings Capt. Obvious's Avatar
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    '99 911 C2, big ass truck, crotch rocket
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    Re: Speedometer Accuracy

    My speedo consistently reads about 3mph faster than I'm actually traveling according to several street signs with radar guns mounted on them near my house.
    -Darrick

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  11. #11
    Veteran Member Four Rings LAZY TURBO's Avatar
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    Jun 01 2005
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    La Crescenta, CA

    Re: Speedometer Accuracy

    mine is off by 3 MPH until i reach 60 MPH, off by 4 MPH after 60MPH.

    kinda off topic, but i was driving down to a long stretch of highway to Palm Springs, i just floored my car up to 137MPH (and then i was scared, and i let go of the gas). is my car even capable of doing that, or my speedo really that off? i have a completely stock USP. Also, i had 3 heads in the car, with my trunk full of bags and vacation shit.
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  12. #12
    Veteran Member Four Rings Redgoat's Avatar
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    Sep 16 2005
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    Seattle

    Re: Speedometer Accuracy

    Mine is off by exactly 5mph.. My speedo will say 20 and i will only be doing 15 I have a PSI3 in the car, and its hooked upto the ECU it told me a different speed, and it matched that of my nav system.. so that was what got me wondering.. a few tests with a calibrated Radar gun.. and it was verified.. i hate knowing this :(
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  13. #13
    Veteran Member Four Rings Capt. Obvious's Avatar
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    '99 911 C2, big ass truck, crotch rocket
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    Re: Speedometer Accuracy

    If it really bothers people that much, check your local phone book for a shop that specializes in speedo calibration. I know in the Seattle area we have Tacoma Speedometer who does really good work.
    -Darrick

    No more Audis, but can't leave this place alone.



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