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Car Forum / BMW Cars / July 2005Speedometer wrong?
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 > 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 how do you know? the easiest fix is to run it for less than 1 hour i.e. keep to 59 minutes max. dj Do you have smaller wheels on it than stock? > 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. 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 >>1991 318is >>As near as I can tell, me speedometer reads 5-10 mph faster than I am [quoted text clipped - 7 lines] > -- > Cliff 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.  SignatureRegards Steve G >>>1991 318is >>>As near as I can tell, me speedometer reads 5-10 mph faster than I am [quoted text clipped - 20 lines] > speedo, of course, depending on the rolling circumference as compared to > the stock sizes. 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? <snip> >>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 [quoted text clipped - 15 lines] > > In this case you'd actually be doing xx - x, no? It was late at night when I composed that (well late for me anyway). 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? SignatureRegards Steve G > It was late at night when I composed that (well late for me anyway). What > I was trying to say is that when the nice policeman stops you for doing 35 [quoted text clipped - 3 lines] > > Does it make sense now? 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. ;-) >>It was late at night when I composed that (well late for me anyway). What >>I was trying to say is that when the nice policeman stops you for doing 35 [quoted text clipped - 8 lines] > If the cops stop you for doing 35 in a 30 your speedo would have been > showing 40mph. ;-) 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. SignatureRegards Steve G > 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. 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. Signature*There are 3 kinds of people: those who can count & those who can't. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. >>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 [quoted text clipped - 12 lines] > 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. 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%. SignatureRegards Steve G > > Crap. ;-) > > [quoted text clipped - 9 lines] > > 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. > 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%. No - the UK regs allow a *totally* accurate speedo - or one that over-reads by the set amount. Signature*Why are a wise man and a wise guy opposites? Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. This is because the government takes care of our wallets. So we drive 7 km/h below the legal limit :-))))))) [...] > Mental adjustment would be your best bet. For some reason, many > Beamers' speedos read high, including mine [...] > Cliff > 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 As the BMW stealers are wont to say: "they all do that." -Fred W 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 > 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 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. > 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 >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. My speedo is about 4mph high at 70 but the odometer is dead on... > >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. > > My speedo is about 4mph high at 70 but the odometer is dead on... 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. >> >belong, but not always. When you see a Call Box, there should be a sign >in [quoted text clipped - 14 lines] >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. 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! > 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 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... > 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. Speedo's read high by default. In my '92 535 it's about 5%, measured with GPS. On my old '86 323 it was between 10 and 15%! > Matt Ulf On my '94 540i, I set the speed limit on OBC to 132klm/h and when it sounds, the needle is at 140k! >> 1991 318is >> As near as I can tell, me speedometer reads 5-10 mph faster than I am [quoted text clipped - 7 lines] >> > Ulf > On my '94 540i, I set the speed limit on OBC to 132klm/h and when it sounds, > the needle is at 140k! I have the same experience. Had the limit set at 95 mph, didn't come on until 100. Then I lowered it to 90 mph, and then it was 93 instead... Obviously the car "knows" that the speedo is off. >>>1991 318is >>>As near as I can tell, me speedometer reads 5-10 mph faster than I am [quoted text clipped - 7 lines] >> >>Ulf Ulf on my '92 325 my digital speedometer reads 93 kilometers an hour while my analog speedometer reads 100. By inserting a code in my obc a got a little more functions, like a digital speedometer. To bad the 2 don't show the same speed Erik >> On my '94 540i, I set the speed limit on OBC to 132klm/h and when it sounds, >> the needle is at 140k! [quoted text clipped - 16 lines] >> >Ulf I'll bet the digital is correct. US DOT requires speedometers to be -0 to +5% so most manufacturers intentionally make them about +3% to be safe. -jim > on my '92 325 my digital speedometer reads 93 kilometers an hour while > my analog speedometer reads 100. By inserting a code in my obc a got a [quoted text clipped - 23 lines] >>> >>Ulf > I'll bet the digital is correct. US DOT requires speedometers to be -0 to > +5% so most manufacturers intentionally make them about +3% to be safe. Do you have a source for this? The only regulation I can find states that "Every bus, truck, and truck-tractor shall be equipped with a speedometer indicating vehicle speed in miles per hour, which shall be operative with reasonable accuracy;" When did the US DOT decide on -0 to +5%? Tom > The only regulation I can find states that "Every bus, truck, and > truck-tractor shall be equipped with a speedometer indicating vehicle > speed in miles per hour, which shall be operative with reasonable > accuracy;" And 'they' don't define 'reasonable accuracy'? The first speedometers were chronometric - rather like a clock movement. By the time cars were on the scene, it would be a poor clock that was 10% out - after all, that would be near 2.5 hours per day. ;-) Later ones were eddy current types - a magnet was rotated within a non magnetic drum. Which pulled it round against a spring, or series of springs, and these could be as accurate as the maker's tolerances and design. Current types are pulse counting. They might use an ABS disc, or a separate generator. You can buy a pulse counting meter which is accurate to within 1% for pennies these days. BMW make their speedos over-read deliberately. There is no country in the world that I know of which requires this. The UK requires a speedo to be accurate or 'fast'. -0%, +10% at 30 mph. If it were merely production tolerances then some would be accurate, and some fast up to the limit. But all are fast. Signature*It ain't the size, it's... er... no, it IS ..the size. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. I have a 95 Maxima. I read this conference so that I can get a feel for the BMW machines, I plan to purchase one in the next year. Having read this about the cars reading over, I find it odd. Occasionally the police drop a Radar Sign on the local roads near my place. I don't know why. I have taken advantage of this facility though and have found that at 50, 60, 80, 100 and 120 Km/h, my speedometer is bang on. I would have hoped that BMW, charging a premium dollar for their cars would at least be able to make an accurate speedometer. rtt > > The only regulation I can find states that "Every bus, truck, and > > truck-tractor shall be equipped with a speedometer indicating vehicle [quoted text clipped - 21 lines] > tolerances then some would be accurate, and some fast up to the limit. But > all are fast. >I have a 95 Maxima. > I read this conference so that I can get a feel for the BMW machines, I [quoted text clipped - 10 lines] > would > at least be able to make an accurate speedometer. For what its worth - by checking with radar signs, timing over measured miles, and comparing with the accurate readings from the on board computer, I've found the following BMW speedo errors (all with OEM tires): 1997 Z3: approx. 5% high 1999 328i: accurate within 1% 2003 Z4: approx. 3% high And as others have said, it is better to be misled by a high reading than a low one, especially when you can easily check it with the OBC. Of course, the BMW /6 cycle I owned 30 years ago read 122 mph at a true 100, but things have improved since then! Tom > I have a 95 Maxima. > I read this conference so that I can get a feel for the BMW machines, I plan [quoted text clipped - 7 lines] > I would have hoped that BMW, charging a premium dollar for their cars would > at least be able to make an accurate speedometer. It isn't an issue of if they can or not. They can, they just don't. It is common practice that the speedometer will read on the high side because the deep-pockets rulings of recent years might hold the automaker responsible if the car was really going faster than the speedo said, so they make sure the car is going slower. Thank the lawyers, not the engineers. > It isn't an issue of if they can or not. They can, they just don't. It > is common practice that the speedometer will read on the high side > because the deep-pockets rulings of recent years might hold the > automaker responsible if the car was really going faster than the speedo > said, so they make sure the car is going slower. Thank the lawyers, not > the engineers. Why not just make it accurate? After all, the lawyers will only have your word as to what it was reading. So it makes no difference what it actually reads. If you were quibbling about a needle's width, possibly. But we're not. Signature*Men are from Earth, women are from Earth. Deal with it. Dave Plowman dave@davenoise.co.uk London SW To e-mail, change noise into sound. |
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