My Speedometer is 2 mps too fast
03-28-2017, 07:12 PM
#33
Instructor
German car manufacturers, especially, intentionally set their speedometers to over read the true mph/kph. In BMWs you can actually code this out, the most common and easiest way being to buy an OBD II device with software from a company named "Carly." This company has started to produce similar products for other brands such as VW, but I don't know how far along they are in that process. Amazon sells the device for BMWs on their website, and the software can be bought through Android Play and the Apple App Store.
With BMWs, you can't code out the over-reading on the analog speedometer, only on the digital one. If you do this, as I have done now on 3 vehicles, if you were going, say, 75 as measured accurately with a radar gun or gps, your analog speedo might read 78 or 81 or even higher, whereas your digital reading would be correct. The cruise control remains similarly uncorrected, so if you set it in this example to actually go 75, the cruise control indicator would say that the speed setting was really whatever the analog speedo reads, e.g. 78 or 81 or whatever.
BMW dealers WILL NOT code this out, they will tell you that it is a "safety feature" and that they cannot code it out due to "liability concerns," more or less the same thing they will tell you if you try to get them to deactivate the seat belt chime (which can also be coded out, on BMWs, with the Carly app and with raw code, also).
I have read that this sort of coding is not available for Porsche automobiles, and I have not researched it.
VWs are reputed not to intentionally over read the speed, and in my own experience this has been correct and my VWs have been spot on.
With BMWs, you can't code out the over-reading on the analog speedometer, only on the digital one. If you do this, as I have done now on 3 vehicles, if you were going, say, 75 as measured accurately with a radar gun or gps, your analog speedo might read 78 or 81 or even higher, whereas your digital reading would be correct. The cruise control remains similarly uncorrected, so if you set it in this example to actually go 75, the cruise control indicator would say that the speed setting was really whatever the analog speedo reads, e.g. 78 or 81 or whatever.
BMW dealers WILL NOT code this out, they will tell you that it is a "safety feature" and that they cannot code it out due to "liability concerns," more or less the same thing they will tell you if you try to get them to deactivate the seat belt chime (which can also be coded out, on BMWs, with the Carly app and with raw code, also).
I have read that this sort of coding is not available for Porsche automobiles, and I have not researched it.
VWs are reputed not to intentionally over read the speed, and in my own experience this has been correct and my VWs have been spot on.
I had a long discussion with the BMW dealer about this regarding my e90. They actually call it "Speedometer Advance" and they have service bulletins about it due to the number of customers asking about the error. The dealer will not code it out, and if I recall correctly they don't have the software to code it out.
I now have had access to the cracked dealer and factory software that will code e46 (and I think e90 as well). On my e46, I believe using the factory-level software, we removed the "Speedometer Advance" - this corrected the analogue gauge. If I recall correctly, there was actually a check box that applied or removed this adjustment.
03-29-2017, 03:33 AM
#36
Poseur
Rennlist Member
Rennlist Member
Welcome to the **** excessive world of Porsche ownership. Yes, the speedometers are 2 mph on the optimistic side--intensionally. Years ago there was actually a DOT regulation that forced manufacturers to fudge on the optimistic side. It's frustrating when I have to mentally do the math all the time.
However, on the German excessive engineering side, the 997 may be reporting the speed 2 mph on the high side but the inner workings of the car all are based on the real speed. For example, the tail will not come up at 75 INDICATED. It comes up at a true 75 mph (which is about 77 mph).
(This actually drives some of my fellow Porsche Pushers crazy when we go out for a drive and my tail simply never goes up. They think it's broken! I just watch to avoid an indicated speed over 76 because I'm trying to avoid deployment of the tail if not needed which in aeronautical terms, adds 'parasitic drag' to the car, impacting mileage. I intentionally do deploy my tail prematurely when road conditions warrant it).
However, on the German excessive engineering side, the 997 may be reporting the speed 2 mph on the high side but the inner workings of the car all are based on the real speed. For example, the tail will not come up at 75 INDICATED. It comes up at a true 75 mph (which is about 77 mph).
(This actually drives some of my fellow Porsche Pushers crazy when we go out for a drive and my tail simply never goes up. They think it's broken! I just watch to avoid an indicated speed over 76 because I'm trying to avoid deployment of the tail if not needed which in aeronautical terms, adds 'parasitic drag' to the car, impacting mileage. I intentionally do deploy my tail prematurely when road conditions warrant it).
03-29-2017, 05:38 PM
#39
Drifting
No kidding!! I can see how his may be an interesting academic question but actually getting upset about it seems, well, a little bit ..... ****
It has effectively no real world implications positive or negative. If I am speeding then I am not too worried about 2mph
It has effectively no real world implications positive or negative. If I am speeding then I am not too worried about 2mph
03-29-2017, 06:35 PM
#40
Instructor
IMHO, all cars should be required to show actual speed. In this day and age of electronic speedos unintentional inaccuracy seems to be rare if not non-existent. I have not had a car made in the last 20 years that had an inaccurate speedo, other than German cars. My 2001 Boxster read 7km/h high at 100km/h, and my BMWs a little less. I don't remember how far off the 997.2 is.
IMHO, show me the real speed and let me decide how fast I want to go (and the ticket I want to risk, or not).
IMHO, show me the real speed and let me decide how fast I want to go (and the ticket I want to risk, or not).