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Inaccurate Speedo and fuel trip
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    Posted: 24 Oct 2006 at 8:56pm
I am convinced that my speedo is over reading by around 5 to 7% on my 120d auto.
 
I have confirmed this by both my Tom Tom and also driving my car on a measured mile.
 
My also getting a similar inaccurate fuel consumption than the average MPG fuel trip.
 
I was wondering if anyone else has experianced the same issue?
 
Kind regards,
 
 
Richard
Colchester
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Mike Fishwick View Drop Down
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Points: 2753 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Mike Fishwick Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 2006 at 10:33am
The BMW tolerance for a speedo is up to 10% plus 2 mph fast, so yours is in the middle of the 'acceptable' band.
 
This is a pretty poor level of accuracy for a system which is almost completely digital, apart frm the final digital to analogue converter chip and the instrument itself.  BS spec for industrial-type meters requires 1.5 %.
 
It's probably a trick on behalf of governments - if the poilice can have accurate speedometers, why can't the public?  Perhaps accuracy will improve as the rear tyres wear down.
 
My Z3 reads 70 mph at 68 mph, which is pretty good.


Edited by Mike Fishwick - 12 Mar 2007 at 11:57am
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 2006 at 3:24pm
Thanks Mike,
 
As it's a electronic system I wonder if it possible for the dealer to adjust, I'll have to wait for my first service to find out.
 
It also explains why my 0-60 time is superior to whats quoted in the book.
 
Thanks,
 
 
Richard
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 25 Oct 2006 at 5:06pm
Not sure about the speedo (unless there is a fault) but the MPG reading can be adjusted. By using the test menu and selecting the right part of the menu (not user friendly) it is possible to alter the % -/+ of the fuel computer.

On most recent BMW's this menu is accessable by depressing the odometer reset then turning the ignition to position 1.

Not sure with the 1 series though.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 2006 at 4:41pm

On my way to work I have to go through a village called Alves which has one of those things that give your speed and a smiley face if under 40 and a frown if over.  I've checked over a period of time to see when I'm actually doing 40 according to the display. I've found that about 43 mph on my speedo is 40mph on the display, that's assuming that the display thing is accurate.  The mpg figures on the computer are a work of fiction, I just check it from full tank to full tank.
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 26 Nov 2006 at 7:49pm
Many thanks for that, that supports my theory that the speedo is 7% out.
 
It will also mean that my MPG consumption will also be 7% worse.
 
I will see what the dealer says when I have my first service.
 
Thanks,
 
 
Richard
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 27 Nov 2006 at 11:45am
Originally posted by Mike Fishwick Mike Fishwick wrote:

 
 
It's probably a trick on behalf of governments - if the poilice can have accurate speedometers, why can't the public?  Perhaps accuracy will improve as the rear tyres wear down.
 
My Z3 reads 70 mph at 68 mph, which is pretty good.
 
I guess its down to cost Mike...the state can fund expensive highly accurate systems but BMW , like most manufacturers, work to an acceptable error rate with whatever they can get away with.
 
Take you Z3 up to flat out and i bet the figure is miles out...my indicated 190MPH on my bike worked out to a genuine 176MPH and an indicated 150MPH in my car worked out to be a true 137MPH..pretty shocking really
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Post Options Post Options   Thanks (0) Thanks(0)   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 22 Jan 2007 at 9:15pm
Interesting progress on my inaccurate speedo, it has been confirmed by the dealer that all models over read by around 7%.
 
Although this is quite handy to avoid speeding it does have many disadvantages including:-
 
  • The mileometer also over reads so my fuel economy is 7% less and not as the claimed figures.
  • It also means my car needs servicing 7% sooner so increased servicing costs.
  • My car reaches it's replacement mileage (120,000 miles) 7% sooner so BMW get a repeat sale sooner.

Perhaps this is why BMW deliberatly makes the speedo over reads, interesting!

 
 
Richard
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MalcolmZ View Drop Down
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Points: 66 		Post Options Post Options   Thanks (0) Thanks(0)   Quote MalcolmZ Quote  Post ReplyReply Direct Link To This Post Posted: 12 Dec 2009 at 9:56am
Hi Richard,
 
I think we have the same car.
 
Like Gordie I pass by a 40-mph smiley checker regularly, and it matches my speedometer reading exactly. So I don't think BMW deliberately over-rate their read-outs. It could be just down to manufacturing tolerances.
840Ci (1994) in the toy box...
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