Bokke

My thought exactly!

Iceman

When the limiter kicks in the speedo is at 256/257 Km/h. So at 250 Km/h the difference is about 6-7 Km/h.

sg530

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).

jeremy

With bigger wheels, the height of the tyre is smaller so the rolling diameter is always the same

cobradav

With bigger wheels, the height of the tyre is smaller so the rolling diameter is always the same
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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.

cobradav

Doppler effect is properlay accounted for in most good radar systems. I get to check out effect in several locations as they like to hide these units on curves and u can see the impact of way off center line to nearly dead on. Pretty good range of angle of attack gets consistent readings - easily in the 15-25 degree off center will be accurately compensated. Consistent with my experiences in radar tracking missiles and satellites for 40 some years. Although these radars are fairly narrow beam width they are at significantly high frequencies so they have very short wave length (down in the mm). Hence they are able to discriminate doppler effect much more effectively. One of the primary reasons they moved up in frequency from the older X-band to the K and Ka bands. Still, many state legislatures mandate at least a 7 mph over posted speed margin before allowing ticketing using radar. Timing traps and clocking by following a minimum distance are considered more accurate. I have not followed the laser physics as yet as I have yet to run afoul of them and hope not to.

Rich535d

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?

Nomis

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?

Rich535d

Wow
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 How many people did you have in the car?
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'

Nomis

Wow
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 How many people did you have in the car?
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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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?.