'06 325xi Speedometer Inaccuracy

In the UK it is up to 10% over but under is not allowed.

Odometer is usually more accurate - check.

Have you changed the wheels?

Why do you assume the mileometer over-reads by the same degree as the speedo?

It is allowed, legal, and preferable to the vast majority of drivers. When sailing down the highway with a speedo reading of 70, actually doing 65 is much better than actually doing 75.

First, it annoys the hell

If you obeay the signs by using the speedo as youir guide, you will never speed.

Second, it's a leased car with 15k per

Get over it.

One fix is to get tires that are a bit bigger around, this will cause the speedo to slow down a bit.

No class action is available.

You seem to be a bit foggy on the actual error rate. If you use a stop watch and a measured mile, you can easily find the actual speed. There are mile markers along the side of all interstate highways, and all state highways that I know of -- I conceed the point that your state highways may not have mile markers, but I'm certain that your state has interstate highways. In any case, set the cruise control so the speedo reads precisely 70, or whatever speed you want to measure, and start the stopwatch as you pass a mile marker, then stop the stopwatch when you pass the next mile marker. Obviously, your start and stop points will not be very accurate, but they are more than accurate enough to determine youir speed -- especially when you repeat the same test a few times and average the results.

Divide 3600 by the time it takes to travel one mile, the result is yoru actual speed. A measured mile at 70 mph will take 51.42 seconds, if your result is 53 seconds, then your actual speed is 67.9, which is only 2 mph below the set speed. I can't imagine what sort of complaint you could raise with an accuracy rate of 97%.

You could also carry your GPS and get an accurate reading from that. Surely you will find that if you observe the limits on the signs, and set the speedo accordingly, you will NEVER get a speeding ticket because the car lied to you.

Standard BMW error, and well within tolerance. BMW will not address it unless it is 10 MPH less, or 1 MPH greater. If you have the computer, it is generally more accurate.

BMW feels it is safer that way.

Odometer generally reads correctly. It is taken differently.

You can adjust it by:

1. Removing the needle, and reinstalling it in a different place. Dumb idea, it's been done.
2. Using a tire calculator, purchase a different size tire. Your odometer will be off.
3. Live with it. Most BMW owners live with it.

Perhaps better to get a passenger to deal with the stopwatch?

Or compare the speedo reading with the speed indicated by a GPS unit.

Andrew

I easily operated the stop watch as I drove. If one selects a speed that divides evenly into 3600 (80 mph = 45 seconds, 60 mph = 60 seconds, 75 mph =

48 seconds) then one can more easily predict where the next mile marker is going to be, and the stop watch becomes a "confirmation point" and a few tenths of a second either way won't matter much.

Using a GPS is easier, and is continuous, but if one hasn't got a GPS or a stop watch, a new stop watch costs about 10 bucks, the GPS costs about 100.

Thanks for answers. If I read it write, some of you are saying that odometer is not taken off the same data as the speedo therefore my lease mileage will be accurate? I'll do the milepoint calculation or use a GPS when I have a chance. I've owned 2 Audi's, a Volvo and assorted other cars and not one has had an inaccurate speedometer much less had it intentionally. I like the car but this is a silly, unnecessary flaw.

I've not owned any of those cars, but I am pretty sure that all of them have the same "flaw." Perhaps the error rate is not as great as you think the BMW's error is, but I am not sure the BMW's error is as much as you think. I have a '94 3 Series (my second one) and the speedo says 80, and a measured mile takes about 46 seconds. My daughter has an E46, but I haven't timed a mile ...

I clocked the BMW on the highway matching speed with my wife in our Grand Cherokee. At 80 MPH it read 7 MPG over the Jeep. None of my cars have ever had any noticable speedometer issue. When I'm on a major highway doing 80 MPH and multiple cars are passing me consistently, something's not right.

Most cars have inaccurate speedometers, but generally have odometers accurate to 1~2%. Of the 3 BMW autos I've owned, the average speedometer error has been small - roughly 4%, or 2 1/2 mph at 60. As a matter of fact Road & Track magazine used publish the speedometer error for every auto tested and Motorcycle Consumer News still does for their motorcycle tests.

If this is your first car with a speedo error, you've led a charmed life!

Tom K.

It's my 1st with a highly noticable one. My life may be charmed but I'm still disgruntled over this issue. Of course, I'm not saying I was ever gruntled to begin with.

That is not an accurate means of testing. It requires the pace car to be accurate, but you haven't confirmed that yet. You have gathered anecdotal evidence at best. If the BMW was wrong by 4 mph and the Jeep was wrong by 3, the difference would be 7, but both would be accurate enough that you'd never know there was an error.

None of my cars have ever

"Schmoe" wrote

That's not quite an accurate (;->) statement. Both take data from the same source (speed sensor). However, the speedometer reading is

*purposely* biased to read high by BMW.

Your Audi and Volvo had the same "flaw". The EU's regulatory body requires that speedometers never read lower than the actual speed, and never more than 10% fast. The US has a +-10% (or something similar) standard. The result is that *all* European manufacturers have designed their speedos to read high. BMW is one of the worst, however. Our Porsche is 2% high, for instance, and BMW could meet that, but hasn't.

FloydR

Calibration is always a good thing.

Then you have been tremendously lucky. One of my five Audis was 10% off on everything. None were dead accurate. My Volvo ownership was too long ago to recall. My BMWs are usually off by 3-5 mph or so, depending on the tires and wheels I'm running.

I don't know about *your* Grand Cherokee, but *my* Grand Cherokee (on stock wheels & tires) reads about 3 mph high at an indicated 65. I confirmed that today with my GPS. But that's no way to calibrate your speedo anyway. Take it out and drive a nearly flat stretch of interstate highway at a set speed (use your cruise control) for as long as you can, noting the time and the number of mileposts you pass. I like to get at least 10, since I know even those posts are not closely calibrated. But over a long stretch, the precision gets better. Then, do the math to see how far off you really are. Then, get over it. We all do.

Yeah ... but I'm not goin' there now. =;^)

-- C.R. Krieger (Been there; done that)

They share a sensor, but how that information is interpreted by the two different readers doesn't have to be the same. If you think for a moment, the needle on the speedo is fixed to a pivot. Move it relative to that pivot and you could make it read near anything at a fixed speed...

Many cars do have over-reading speedos. Makes for easy bar room betting. ;-) You need to find a mag that tests the speedos as part of a comprehensive road test. It's interesting that many older cars with electro/mechanical units (eddy current) were pretty accurate. Modern pulse counting types *should* be more so. That some aren't has to be deliberate.

I understand that which is why I intend to further test with GPS, stopwatch and a different pace car.

I suppose, at the very least, this is the answer I was expecting though is doesn't seem right that an automobile of this caliber should be that far off. I'll live with it of course but would take it into consideration when it comes time to replace the Jeep. I have been considering the 530xi wagon. The car has a few other minor electrical quirks which I'll assume BMW will fix next time it's in for service but the speedo thing is annoying. I live in an region of heavy radar usage/taxation and I'd like to know exactly what I'm doing. Maybe a portable GPS is the answer for the run of the lease (another 2 years 9 months).

Again, thanks to all for their input.

Speedo accuracy is determined by many things. In the UK and other countries too I think a speed indicator device must be within 10% @ 30 MPH (legal town limit) therefore this could mean 33MPH or 27MPH - not enough to worry anyone but @ 70 MPH this can mean 77 or 63 so it is noticeable and @ 100 it's 90 or 110.

The odometer on a mechanical rotating magnetic drum device is gear driven so no slippage and if correct tyres and axle ratios are used the mileage should be pretty accurate. The rotating magnets in the alloy drum pulling against a spring is pretty inaccurate and depends on the spring and friction or rather the magnetic flux field . As the tension on the spring is increased so the effort to move the pointer (attached to the alloy drum spindle) is increased and this is NOT linear but not quite logarithmic either - just mechanical Dufor accuracy (do for now).

Mechanical speedos can only be accurate at one speed and everything else is Dufor. Electronic speedos and I mean REAL electronic speedos can be pretty accurate but the cost to be 100% is too much as they don't HAVE to be. If government dictated they have to be 100% accurate at all speeds for all conditions - winter tyres - summer tyres - auto - manual transmissions then there would be mayhem.

Live with it unless it over 10%. I think the BMW can be adjusted electronically as the pickup is in the rear diff unit but it's a dealer jobby or someone with the right software which is available for about 3K GB Pounds.

Sir Hugh of Bognor

The difference between men and boys is the price of their toys. Intelligence is not knowing the answer but knowing where and how to find it!

Hugh Gundersen snipped-for-privacy@h-gee.co.uk Bognor Regis, W.Sussex, England, UK