I have a 2006 E90 (330xi).
I had heard from another owner of an E90 at work, that his speedometer reads
high, compared to what he was getting on his portable GPS.
I tried same (using a Garmin Gecko 201) and also noticed the speedo reads
4-5 MPH higher. For example, at 70MPH on the speedo (held to that by the
cruise control), the Garmin showed 65-66 MPH. At 75MPH on the speedo (also
held by cruise), the GPS showed 70-71 MPH. Less difference at the lower
speeds - 40MPH on the speedo is 37-38 on the GPS. (And for those GPS savvy,
I did have the Gecko set at the more accurate GPS "WAAS" mode, aka
While a speedometer reading high is a good "safety margin" for lessening the
risk of getting a speeding ticket, I'd still rather the speedo be as
accurate as possible. A BMW of all cars should have nearly a dead-accurate
Has anyone had any luck getting BMW to recalibreate your speedo
electronically at the dealer? It's still under warranty.
The speedo reading matches the cruise control hold speed, but together they
are off when compared to GPS.
This is normal. The speedo is not having an error because they can't make it
accurate, it is having an error because they made it that way on purpose.
You pointed out that it is a safety margin against speeding tickets.
Deja vu (search group).
The speedo (high for legal reasons - only -3 to + 10% allowed), speed limit
check and true speed (by calibration against markers or by GPS) are all
The speedo is affected by tyre size and wear.
IMX BMW speedos read about 5-7% high, speed warning about 2-3%.
I have a spare speedo head from an e30 in my shop and I do notice that it
has a trim potentiometer on the circuit board. There's no easy way to be
sure that it's an adjustment for gain but I can't really think of anything
else that would need to be adjustable on a speedometer. Access to this
adjustment would require removal of the instrument cluster from the car and
removal of the speedo head from the instrument cluster so it must have been
set when the speedo head was manufactured. It wouldn't surprise me if
someone had experimented with this to see what it does. You might try
googling for it.
I agree with you that it is wrong to make the speedo read high just so we
can all feel a little naughty without having to pay for tickets. The
engineer's rationale probably includes adding up all the adverse tolerances
that could occur to relevant components over time; accounting for someone
installing oversize tires; throw in another mph for parallax; and then one
more mph to make sure it never reads low.
Now that the odometers are also electronic I wonder if they read long
because of the skewed speedometer readings. Does your gps agree with the
Most are guaranteed to be accurate @ 30mph or within 10% Apparently if you have
the know how you can re calibrate via the on board computer The E38 with the
business radio system can be used but I have lost all the paperwork I used to
have but I know it's available on the net somewhere - Unix Nerd might have some
I own a 1990 E30 convertible and like every car I have ever owned
according to my gps it also reads high.
But I am sure it is deliberate. The reason is this:- according to my
owner's manual my auto transmission should "lock up" at 53mph. It does
so at an indicated 58mph BUT my gps correctly puts this at 53mph. MY
BMW IS FULLY AWARE OF WHAT SPEED IT IS DOING. It is just laziness on the
part of motor manufacturers to display an accurate speed. Modern
engineering can measure distances to millionths of an inch; time to
millionths of a second weights and measures to unbelievable accuracy.
Are you telling me that some of the best engineers in the world can't be
sure of a car's speed to +/- 10% or so - nonesense. You wouldn't buy a
beer glass that might/might not be a pint or a thermometer that tells
you an approximation of the temperature or maybe more appropriately a
tyre that fits the rim of your wheel to +/- 10%; so why produce a
scientific instrument like a speedometer that indicates the speed that
somebody else is doing???
I'll get off my soap box now.
And I'll get on mine about the EU regulators, whose fault these
inaccurate reading speedos are. The EU - and I note that YOU,
David, are in the UK are hence part of the problem set - in it's
wisdom has said that speedos can never read high. So we're stuck
with speedos that read low *BY DESIGN* of some random
paper-pushers that you (indirectly) hired.
You said "in it's wisdom has said that speedos can never read 'high' " -
surely you mean 'low'??
You said "so we're stuck with speedos that read 'low' *BY DESIGN* " -
surely you mean 'high'
See elsewhere in this thread about legislation, wheel sizes, tyre profiles
Not only did you get it the wrong way round - speedos are not meant to read
low, so we are stuck with speedos that read high by design*, and this is
IIRC part of the MOT test, but of course this arises from UK Construction
and Use regulations, getting on a for half a century old, not the relatively
small number of Eurocrats.
Amusingly you post your anti European tirade in a BMW group. It may have
escaped your notice (and judging on the basis of your post, not much gets
past your prejudices) that apart from the Mini, that they took over and
revamped**, BMW's are made in Bavaria, Germany, which is in continental
Europe, so regulars in this group, most of whom own BMW's are already
convinced of their superiority to UK cars and you are banging your head on a
brick wall (some more).
* years ago Ford used to take this to extremes, so that you thought your car
was going faster than it could,
** I had a lift in an 07 model yesterday. Excellent, with very low
emissions and technology that worked.
I've already acknowledged that I wrote it wrong. Too bad you replied
before reading that.
I've owned BMWs (and Porsches) for 30 years; have you?
My rant was mostly an attempt at a humorous-counter-rant to David,
not against the EU/UK members of this group. It's always fun to
raise the ire of that group.
On Fri, 6 Jul 2007 21:15:05 +0100, "R. Mark Clayton"
That why I bought one -------- new 730d SE loaded.
However back to speedo's - back in the bygone days of the mid 60's - early 80's
I used to tune, build fast cars and latterly design and fit turbo systems for a
couple of manufactures of imported cars. When we did major mods like replacing
rear axles to handle the power, tidy up 'hot-rods' so the went as fast as they
looked, changing axle/final drive ratios to give realistic fuel/performance
combinations we had to re calibrate the speedometer.
An independent company at that time was "Thomas Richfield" operating off Great
Portland Street in central London. The equipment they used was not as
scientific as one would imagine but it worked. All they wanted was the rolling
radius of the driving wheel (remembering that all speed measuring was done from
the gearbox at that time) and the distance covered by one revolution of the said
wheel and the number of turns of the propshaft (not many cars were FWD).
Every one we had re calibrated was accurate @ 30 mph and no more than 3% @ 70
mph only one time checked a car at over 140 and the speedo was reading 142. Not
bad at the time.
However, history has failed us.......... Thomas Richfield was bought out by
Smith's Industries - Transferred to LUCAS (Ho Ho) and on its demise to TRW
Thomas Richfield was sold off to Speedograph a one time accessory manufacturer
Gone are the days of the backroom genius..............
Sir Hugh of Bognor
The difference between men and boys is the price of their toys.
On Sat, 07 Jul 2007 08:37:40 +0100, email@example.com wrote:
Oops! Just remembered not the propshaft but the speedo drive cable. How many
time inc parts of a turn for one revolution of one back or front wheel (FWD such
as Mini and most BL transverse vehicles of the day)
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