Speedometer wrong?

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1991 318is As near as I can tell, me speedometer reads 5-10 mph faster than I am actually going. Was wonderng if there is any hope of fixing this or if I
just need to make the mental adjustment. Thanks.
Matt
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how do you know?
the easiest fix is to run it for less than 1 hour i.e. keep to 59 minutes max.
dj
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Do you have smaller wheels on it than stock?
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MWarren wrote:

Mental adjustment would be your best bet. For some reason, many Beamers' speedos read high, including mine. This subject has been discussed here previously.
-- Cliff
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snipped-for-privacy@yahoo.com wrote:

If you live in Europe ALL speedometers (should) read faster than you are actually going ... it's a legal requirement and explains why the needle on many speedos start above zero. It also explains why when you say to the nice policeman "but my speedo only showed xx mph" and he's booking you for xx+5 he doesn't believe you :-)
In the UK you can check the Construction and Use Regulations, but from memory current requirements are for the speedo to read <6% high; 0% low.
Having non-standard wheels and tyres can effect the accuracy of the speedo, of course, depending on the rolling circumference as compared to the stock sizes.
--
Regards

Steve G
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wrote:

Steve, think you had better read this bit again ..... "(should) read faster than you are actually going .....but my speedo only showed xx mph and he's booking you for xx+5 he doesn't believe you"
In this case you'd actually be doing xx - x, no?
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zerouali wrote: <snip>

What I was trying to say is that when the nice policeman stops you for doing 35 in a 30 zone and you try to plead that your speedo was only registering 30 then he isn't going to believe you because your speedo is designed to read higher than you're actually going.
Does it make sense now?
--
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Steve G
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No mate, if your speedo is reading higher than you're going then you should never be caught speeding. If the cops stop you for doing 35 in a 30 your speedo would have been showing 40mph. ;-)
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zerouali wrote:

Yes I understand that. I was trying to emphasise that because the speedo reads high by design (i.e. to comply with legislation) trying to tell the police that your speedo was reading less than you were actually travelling won't be accepted as an excuse because he/she (the police officer, that is) knows that's not true.
--
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Steve G
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Crap. ;-)
I've got a UK car (not a BMW) where the speedo is accurate.
The requirement is that it shouldn't under-read. From the days of mechanical devices.
In these days of pulse counting types, the idea of having a speedo which is 10% out is ludicrous. 1% high or so when new would cope with tyre wear.
It suits the car makers to have speedos that read high - "my car can easily do 100 mph" or similar, while the actual top speed might be 90.
--
*There are 3 kinds of people: those who can count & those who can't.

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Dave Plowman (News) wrote:

Not manure. Check the current construction and use regulations. The wording is such that to comply fully the speedo has to read over even if it's by as little as 0.1% - which I would consider to be "accurate". I also have a non-BMW car in which the speedo is (as far as is measurable without specialist timing devices) about 2% out between 30 and 70mph. I haven't checked it outside of this range. I never mentioned 10%.
--
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Steve G
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No - the UK regs allow a *totally* accurate speedo - or one that over-reads by the set amount.
--
*Why are a wise man and a wise guy opposites?

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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This is because the government takes care of our wallets. So we drive 7 km/h below the legal limit :-)))))))
[...]

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MWarren wrote:

As the BMW stealers are wont to say: "they all do that."
-Fred W
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Germany has a law that requires no speedometer be pessimistic in its speed reading. Sooo, BMW chooses to insure they are in compliance by installing optimistic speedometers. Typically 5 mph in the 65-75 mph range.
R / John

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It should read faster than you are going. This keeps you from going too fast.
If the signs say 45, and your speedo says 45 but you are really doing 40, then you will never get a ticket if the speedo never goes above the number on the sign.
You can calibrate your speedo with a stop watch and your Cruise Control. Set the Cruise to 80, then measure the time it takes to go a mile. It should take 45 seconds. The miles are marked on the side of the freeways. If you watch the right shoulder, you will see signs that count down as you go south or west. Typically a Call Box will be placed where one of these signs would belong, but not always. When you see a Call Box, there should be a sign in one half mile because the signs are normally placed at half-mile intervals. Do not use the odometer to click the miles off because if the speedo is having an error, the odometer will have an error too.
You can use the signs to check your odometer (trip meter), and with a stop watch, you can calibrate your speedo. There are 3600 seconds in an hour, so if you divide 3600 by the time it takes to go a mile -- 360 / 40 = 90 mph, 3600 / 45 = 80 mph, 3600 / 48 = 75 mph, 3600 / 51.43 = 70 mph, 3600 / 60 60 mph. Alternatively, 3600 / 80 mph = 45 seconds. You can set your Cruise, and divide 3600 by the setting of the cruise to calculate the time it takes for the mile markers to whiz by, and use the stop watch to see where the markers should be.
My speedometer is very nearly perfect between 60 and 90, myj guess is that it is accurate across the entire range -- but this is speculation. You didn't say what size tires you are running, but if your tires are too small, then the speedo will be too fast.

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On Tue, 14 Jun 2005 14:57:49 -0700, "Jeff Strickland"

My speedo is about 4mph high at 70 but the odometer is dead on...
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wrote:

That sounds about right. My odo is also dead nuts on, but my speedo is only off by about 1.5mph at 80. Over my 40+ mile commute, I think my odo is a little on the high side, but I'd have to keep a log of the mile markers and I just don't care that much ...
If the OP's speedo is off by the margin he claims, then he should calibrate the speedo by the mile markers. If he wants to check the odo, and finds that it is accurate, then he can calibrate the speedo from it as a mind-game while he wiles away the hours going to work and back.
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On Tue, 14 Jun 2005 16:20:35 -0700, "Jeff Strickland"

I checked mine after I replaced the gears (89 325i) in the speedo and on a 65 mile trip (by the mile markers) the odo was dead on. I wouldn't go through the hassle on a short trip either but I figured what the hell, I've got a straight interstate drive, I'll have a look!
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Typically they are 7% high. I would suggest that you calibrate both the speedo and the speed warning device (in the computer) against the 100m markers posts on a motorway near you.
If you posted from the USA, then I should tuck a picture of that early exponent of liberty and freedom (Benjamin Franklin) near your driver's license...
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