How accurate is the speedometer
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Originally Posted by Merv the Derv' date='May 31 2005, 10:39 AM
Who cares -? You're doing almost 160mph in a diesel
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I used my portable gps (imagine having measured vehicle speed using the car's gps ! <_< ) to calibrate speedometers. Even before I got my 5, I was finding the Japanese cars were very accurate and GM and Ford varied (up and down) in error several percent as the speed changed but my old Chrysler was proportionately high by a about one percent of speed until about 60, then accurate at higher speeds. Now why do I tell this? Because my gps calibration of my 5 shows that between 30 and 70, the error is a constant (within practical limits) 2 mph high. Below 30, it's 1, and above 70 it goes to 3 high (roughly). My observation is that the speed seems to be reported as a constant deviation of 2 over actual speed for that practical range of speed. Now I know it doesn't make sense (I am an engineer ) that the speed error is not a constant percentage, but I can't help thinking that first, BMW decreed the speedometer had a built-in error (something I don't agree with for such an otherwise precision machine) and second, the electronics in the car are very sophisticated. For example, I have Nav and while I drive around on the military installation I work in, it can't guide by satellite but accurately knows my position, including turns and distances (many sensors for many measurements like individual wheel rpm and angle). The car knows precisely what it is doing and my interpretation is that the the spedometer computer calculates the speed to display rather than just measures it. I may be wrong, but I have proven this to myself over and over (tire wear and temperatures and weather included).
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Originally Posted by JDN' date='May 31 2005, 03:25 PM
Do you suppose BMW changes the speedo ratio based on 16", 17" or 18" wheels? I bet they don't. Ice - you know?
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Originally Posted by jeremy' date='Jun 1 2005, 05:09 AM
[quote name='JDN' date='May 31 2005, 03:25 PM']Do you suppose BMW changes the speedo ratio based on 16", 17" or 18" wheels? I bet they don't. Ice - you know?
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[/quote]Or close to the same. Its hard to get exactly the same as you move from one diameter wheel/tire ratio to another. Get a list from several tire mfrs and see that they get close but not exact. Also varies - however slightly - from mfr to mfr.
For instance comparing sport (19") with non sport (18") combos using recommended tire sizes resulted in a potential 0.4 inch diameter difference between tire mfrs (limited to Michelin, Bridgestone and Continental comparos) and wheel/tire combos. Only 1.5% max impact so not much, but some, impact. Also as mentioned elsewhere we do suffer tread loss so there will be an ever increasing difference, however slight that is. Some folks use winter set ups where they do not try to make exact matches. Good to know the difference in diameter in percent to keep in mind how that effects speedo.
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Originally Posted by subterFUSE' date='May 31 2005, 09:28 AM
Another issue to remember...
Police radar/laser both operate on the doppler effect.? This means that unless they are directly in your lane of travel, they will read slower speeds than you are actually travelling.... because they will have to read offline a bit.
Police radar/laser both operate on the doppler effect.? This means that unless they are directly in your lane of travel, they will read slower speeds than you are actually travelling.... because they will have to read offline a bit.
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#17
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I have a 'Road Angel' GPS camera locator (it normally lives nowadays in my wife's car). Yes, the BMW speed is pretty accurate (within a few miles per hour). However I haven't tested this at 160 mph yet
I's suggest to Nomis that you get one - you might need it at that speed
Nomis what was the rev counter reading at that speed? Was it close to maximum?
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I's suggest to Nomis that you get one - you might need it at that speed
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Nomis what was the rev counter reading at that speed? Was it close to maximum?
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Rich535d
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
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Originally Posted by Nomis' date='Jun 2 2005, 07:00 AM
Rich535d
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
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I'd better not try this with the wife and kids in the car. I'm glad that you did not take the photo yourself. You said one of your passengers
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I regularly go faster in my E60 than I have in any other car, and yes, the car feels very stable. But I've yet to break the 'twice legal limit'
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Originally Posted by Rich535d' date='Jun 3 2005, 12:12 AM
[quote name='Nomis' date='Jun 2 2005, 07:00 AM']Rich535d
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
The revs were at about 4500 and from where I was sitting the speedo was showing 160 mph. (Photo taken by one of my passengers from the side). The car still felt like it had more left but I was running out of vision. Also it was very stable. I would still be interested in where the limiter is, perhaps on the gearbox?
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I'd better not try this with the wife and kids in the car. I'm glad that you did not take the photo yourself. You said one of your passengers
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I regularly go faster in my E60 than I have in any other car, and yes, the car feels very stable. But I've yet to break the 'twice legal limit'
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[/quote]Two passengers. I was not in the UK at the time, I had three miles of straight empty dual carriageway. Probably wouldn?t try it on the M25, there again?.
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