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Speedo incorrect

Discussion in 'Warranty questions' started by jc1693, Sep 7, 2009.

    • Member

    jc1693

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    I have a 2008 335i with a manual transmission, Sport Package and 18" run flats and it appears my speedo is off by 3mph. The radar set as I enter my base shows 17 mph but my speedo shows 20 mph. Also, on a road trip last week the cruise was set at 85 but my TomTom showed me only going 82, is this normal? I wouldn't think so but...Also, does this have any impact on what my true mileage is on the car? I know for some cars the mph is taken off the transmission and others take it at the wheel, I don't know what BMW uses. Anyone else having the same issue and if so, how did you resolve it? Thanks...
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    sunnyandrich

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    I've always heard BMWs are set to display a lower speed than actual, but can't remember the reason...maybe just urban legend.

    Certainly my car always reads higher than I'm going, whenever I pass by those police "YOUR SPEED IS" trailers that WS PD deploys occasionally...For example, my speedo shows 32.0 and the machine shows 30.0 mph...
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    breadman

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    My speedo is off considerably more than yours. In fact yours sounds very accurate. I pass one of those roadside radar displays from time to time, and if my speedo reads 80 mph then it tells me I am going 72 or 73. IMO the whole situation with the speedometer is ridiculous. This is my first BMW and I still can't get over how bad "the ultimate driving machine" is about giving me unreliable information. The speedometer should tell me exactly how fast I am driving.
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    conechaser

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    Actually, 17/20 and 72/80 is about the same percent of error. Sounds like this could be standard operating procedure for BMW's.

    BIMMIR guest

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    I'm pretty sure all cars are set up this way as a "safety precaution" is how I heard it.
    If you drive with a portable GPS just on the view map setting, you can really see it.
    My '09 328xi is about 3-5 mph depending on how fast I'm going.
    • Member

    az3579

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    Everyone,
    This is on purpose, and is completely normal. EVERY single BMW has this issue and is designed like that (not a defect).

    Don't let it bother you. I don't see what the big deal is.
    It's actually a very good thing that it reads higher. There's less of a chance you'll get into bigger trouble should you get a speeding ticket. The difference between going 5 over and 10 over does matter, and if you're really going 5 over your speedo is probably saying 10 over.
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    steven s

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    Normal for BMW, yes.
    Normal for everyone else? I doubt it.
    My 1990 Mazda MX6 was dead on accurate.

    This is like people who set their clocks ahead so they are not late.
    But if you know the clock is set ahead, what's the point

    Maybe it's conservative to make up for people who use different tires?
    Just like water temp gauges that read 12 o'clock even at WOT on my E36.
    I'd like my instruments to be accurate.
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    Brian A

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    It does not. All other gauges (odometer, trip computer, etc) all use the correct speed to do their calculations. It is only the main speedometer that shows the incorrect higher speed.

    If you have a trip computer that can calculate average MPH, push "reset" while at speed. It will show the correct instantaneous "average" speed which will be lower than what the speedometer is showing.

    Somewhere in this forum is an explanation why BMW does this.
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    • Technical Service Advisor

    mooseheadm5

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    Yup, the explanation is posted in another thread. Basically, in Germany the manufacturer is liable if the speedo reads even 1mph LOW. To account for variability in tire diameters that can be fitted to a car (and still be the "correct" fittment) as well as tire size manufacturing tolerances and tire growth at speed, the speedo is set to read high.
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    sunnyandrich

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    This is exactly the explanation I recall.

    Seems like my MBZ was setup the same way, one suspect's it's a German car thing.
    • Member

    conechaser

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    This must be a BMW thing then. My speedo and odo are both off in both of my (non-BMW) cars.
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    Brian A

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    ... I suppose I am speaking based on my experience with my E30. While I believe the generalization I made above is true, my experience base is limited (BMW DID make cars after the E30 ... didn't they?).
    • Member

    jc1693

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    My speedo issues

    Thanks to everyone for the feedback on my speedo issues, it looks as if this is a "normal" thing for BMWs although I kind of find it kind strange. I even asked the tech department at Bimmer magazine and here was their response...

    You have described normal vehicle operation, not a defect. All BMW speedometers are designed to read up to 10 percent more than the actual road speed. Please see the attached BMW Service Information Bulletin 62 02 96. I don't like to say "they all do that," but in this case it is true.

    BMW swears the error doesn't affect the odometer, but many of my readers -- engineers mostly -- have reported GPS reveals the odometer error is precisely the same as the speedometer error.

    The speedometer and odometer take their input from the left rear wheel speed sensor.

    Best regards,

    Mike Miller
    Bimmer Tech Q&A


    My concern was not the the speedo being off because that can keep me out of trouble with this car (gotta love 2 turbos spinning up :D) but the fact that the mileage on my car is not accurate if the signal for both are coming from the same place which it appears they are. I don't plan to sell the car but if I can keep from going to the dealer any earlier than my odometer says I have to for scheduled maintenance then all the better. I attached the service bulletin that talks about the speedo issues but I am still not convinced the odometer is not affected...
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    breadman

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    It is a defect of judgment on the part of BMW. I would much prefer to see my exact speed. If I am in a 70 mph zone and I see a speed trap, I want to know that 70 mph on the speedo is 70 mph on his radar. Furthermore, if I am in an accident I don't want the black box subpoenaed and have a plaintiff "prove" to the court that I was going 77 mph if I was in fact going 70 mph. Considering how much of a car is electronic this and that nowadays, if they want to pull this crap they should have an electronic speedo that I can choose to set back to exact speed readout.

    /rant. It is easy enough at least to check the odometer with the mile markers on the interstate. Mine seems to show 1:1 for actual miles.
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    CRKrieger

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    That cannot happen absent an ACTUAL manufacturing defect, in which case you would have a cross-claim against BMW ... or did you fail to understand that the intentional error is always in the other direction? The reason is precisely the issue you pose here: Liability for a lower-than-actual reading. When the day comes that you are able to guarantee that BMW will never face such a liability, then they may change the manufacturing tolerance. Until then, the choice of how to address that exposure is theirs.
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    breadman

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    I think you misunderstand my point completely. Let me re-state it as a scenario: Imagine that I am traveling in a 70 mph speed zone, and let's suppose I'm doing 73 mph. Now suppose I am involved in a collision and some other party is injured or even killed, and I end up as the defendant in a civil suit. If I was traveling at 73 mph then a 10% over-estimation of my speed would mean that the speedometer shows a speed of 80.3 mph. If the car records data (some do, some don't and honestly I don't know if my specific BMW has such a black box), then it seems to me that it would represent my speed as 80.3 mph. So now the jury or judge is thinking, ah he was doing 80 in a 70 zone, the maniac. This puts me in the position of convincing a judge or jury that my car over-represents the speed and that I was not in fact exceeding the speed limit by 10 mph.

    http://www.law.com/jsp/article.jsp?id=1105364095740

    http://www.m5board.com/vbulletin/e39-m5-e52-z8-discussion/40054-more-useful-black-box-info.html


    Aside from legalistic paranoia, I simply find it distasteful to have the car give me back information that is wrong. I want to know how fast I am going without having to do math in my head. If I were the captain of a destroyer I wouldn't tolerate the mechanic in the engine room routinely giving me slightly inaccurate reports when I inquired about this or that. The human brain wants reliable data to make decisions. It is stupid to introduce additional calculations. I understand the rationale for the over-reporting of the speed, and I think it is not sufficient to outweigh the drawbacks. Finally, I have checked the digital speed read out on my instrument cluster and it is identical to the needle on the speedo, so there is no way to get the actual speed shown as far as I have been able to determine.
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    az3579

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    You can use a GPS unit to measure actual speed. I know, you shouldn't have to use one to measure actual speed, but if you really need to know, you can check it from one. If you don't have one, then I'm afraid you're SOL. BMW won't change its ways until it can secure a non-liable position on the matter.
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    joelfromoz

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    Interesting stuff. I didn't notice this with my E46, but it's driving me crazy with my E30. I think the speedometer is off 5-7 mph. I threw my GPS in to check it tomorrow.

    I feel like I'm getting run over on the freeway ('course I do sit pretty low), but the local cops also like to sit on the hidden on-ramps - so I'd like to know hpw fast I'm really going.

    Glad to know I'm not alone! :)
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    rspeser

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    I noticed the same problem on a recent trip when I put the GPS in the car. The difference at 70 actual was 75 indicated on the speedo. I was planning on taking the car to the dealer this coming Friday and was going to bring up the problem until I read this thread. Glad I'm not the only one experiencing the problem but also sorry for all of us.

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